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  • 51. Hunt, R
    et al.
    Dance, D
    Pachoud, M
    Alm-Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Sandborg, Michael
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Ullman, Gustaf
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik.
    Verdun, F
    Monte Carlo simulation of a mammographic test phantom2005Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, nr 1-3, s. 432-435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A test phantom, including a wide range of mammographic tissue equivalent materials and test details, was imaged on a digital mammographic system. In order to quantify the effect of scatter on the contrast obtained for the test details, calculations of the scatter-to-primary ratio (S/P) have been made using a Monte Carlo simulation of the digital mammographic imaging chain, grid and test phantom. The results show that the S/P values corresponding to the imaging conditions used were in the range 0.084-0.126. Calculated and measured pixel values in different regions of the image were compared as a validation of the model and showed excellent agreement. The results indicate the potential of Monte Carlo methods in the image quality-patient dose process optimisation, especially in the assessment of imaging conditions not available on standard mammographic units. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 52.
    Kardell, Martin
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Medicinska fakulteten.
    Magnusson, Maria
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Tekniska fakulteten.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Jeuthe, Julius
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Medicinska fakulteten.
    Malusek, Alexandr
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    AUTOMATIC SEGMENTATION OF PELVIS FOR BRACHYTHERAPYOF PROSTATE2016Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, nr 1-4, s. 398-404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Advanced model-based iterative reconstruction algorithms in quantitative computed tomography (CT) perform automatic segmentation of tissues to estimate material properties of the imaged object. Compared with conventional methods, these algorithms may improve quality of reconstructed images and accuracy of radiation treatment planning. Automatic segmentation of tissues is, however, a difficult task. The aim of this work was to develop and evaluate an algorithm that automatically segments tissues in CT images of the male pelvis. The newly developed algorithm (MK2014) combines histogram matching, thresholding, region growing, deformable model and atlas-based registration techniques for the segmentation of bones, adipose tissue, prostate and muscles in CT images. Visual inspection of segmented images showed that the algorithm performed well for the five analysed images. The tissues were identified and outlined with accuracy sufficient for the dual-energy iterative reconstruction algorithm whose aim is to improve the accuracy of radiation treatment planning in brachytherapy of the prostate.

  • 53.
    Kaveckyte, Vaiva
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Benmakhlouf, Hamza
    Karolinska Univ Hosp, Sweden.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Carlsson Tedgren, Åsa
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Suitability of microDiamond detectors for the determination of absorbed dose to water around high-dose-rate Ir-192 brachytherapy sources2018Ingår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, nr 1, s. 429-437Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: Experimental dosimetry of high-dose-rate (HDR) Ir-192 brachytherapy (BT) sources is complicated due to high dose and dose-rate gradients, and softening of photon energy spectrum with depth. A single crystal synthetic diamond detector microDiamond (PTW 60019, Freiburg, Germany) has a small active volume, high sensitivity, direct readout, and nearly water-equivalent active volume. The purpose of this study was to evaluate the suitability of microDiamond detectors for the determination of absorbed dose to water around HDR Ir-192 BT sources. Three microDiamond detectors were used, allowing for the comparison of their properties. Methods: In-phantom measurements were performed using microSelectron and VariSource iX HDR Ir-192 BT treatment units. Their treatment planning systems (TPSs), Oncentra (v. 4.3) and BrachyVision (v. 13.6), respectively, were used to create irradiation plans for a cubic PMMA phantom with the microDiamond positioned at one of three source-to-detector distances (SDDs) (1.5, 2.5, and 5.5 cm) at a time. The source was stepped in increments of 0.5 cm over a total length of 6 cm to yield absorbed dose of 2 Gy at the nominal reference-point of the detector. Detectors were calibrated in Co-60 beam in terms of absorbed dose to water, and Monte Carlo (MC) calculated beam quality correction factors were applied to account for absorbed-dose energy dependence. Phantom correction factors were applied to account for differences in dimensions between the measurement phantom and a water phantom used for absorbed dose calculations made with a TPS. The same measurements were made with all three of the detectors. Additionally, dose-rate dependence and stability of the detectors were evaluated in Co-60 beam. Results: The percentage differences between experimentally determined and TPS-calculated absorbed doses to water were from -1.3% to +2.9%. The values agreed to within experimental uncertainties, which were from 1.9% to 4.3% (k = 2) depending on the detector, SDD and treatment delivery unit. No dose-rate or intrinsic energy dependence corrections were applied. All microDiamonds were comparable in terms of preirradiation dose, stability of the readings and energy response, and showed a good agreement. Conclusions: The results indicate that the microDiamond is potentially suitable for the determination of absorbed dose to water around HDR Ir-192 BT sources and may be used for independent verification of TPSs calculations, as well as for QA measurements of HDR Ir-192 BT treatment delivery units at clinical sites. (C) 2017 American Association of Physicists in Medicine

  • 54.
    Larsson, Peter
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Evaluation of the uncertainties in KAP-meter calibrations1996Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report was prepared in order to give more details to the uncertainty evaluation of the Kerma area product meter calibration procedure described in the paper:

    Larsson J P Persliden J Sandborg S and Alm Carlsson G 1996 Transmission ionization chambers for measurements of air collision kerma integrated over beam area. Factors limiting the accuracy of calibration. Phys. Med. Biol. 41 2381-2398.

    Figures and equations referred to in this report will be found in the paperabove.

    For convenience, however, the equations in the paper that are used in the uncertainty analysis are retyped on the next two sides, see text in section 2.7. in the paper for further details. The numbering of the equations are kept as in the paper.

  • 55.
    Larsson, Peter
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Energy dependence in KAP-meter calibration coefficients: Dependence on calibration method, type of KAP-meter, and added filter close to the KAP-meter2006Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560Artikel i tidskrift (Refereegranskat)
  • 56.
    Larsson, Peter
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Ionization chambers for measuring air kerma integrated over beam area: Deviations in calibration values using simplified calibration methods1998Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, Vol. 43, nr 3, s. 599-607Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Calibrations of kerma-area product meters (KAP meters) are often performed using simplified methods. The accuracy thus obtained can be insufficient, especially when the KAP meters are used for optimizing radiological procedures. The deviations between the best available calibration factor (k) and the simplified calibration factor were measured at different clinical x-ray installations. Depending on the type of x-ray installation and calibration method, the quotient ranged from 0.83 to 1.19, reflecting the error made in practice using these methods. A simple alternative calibration method based on comparison with a KAP meter calibrated by the best available method is described. Depending on tube potential and the stability of the electrometers, the uncertainty in the calibration factor derived with this method was between 3.8% and 5.6% (at 95% confidence level).

  • 57.
    Larsson, Peter
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Transmission ionization chambers for measurements of air collision kerma integrated over beam area. Factors limiting the accuracy of calibration1996Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, Vol. 41, nr 11, s. 2381-2398Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Kerma - area product meters (KAP meters) are frequently used in diagnostic radiology to measure the integral of air-collision kerma over an area perpendicular to the x-ray beam. In this work, a precise method for calibrating a KAP meter to measure is described and calibration factors determined for a broad range of tube potentials (40 - 200 kV). The integral is determined using a large number of TL dosimeters spread over and outside the nominal field area defined as the area within 50% of maximum . The method is compared to a simplified calibration method which approximates the integral by multiplying the kerma in the centre of the field by the nominal field area . While the calibration factor using the precise method is independent of field area and distance from the source, that using the simplified method depends on both. This can be accounted for by field inhomogeneities caused by the heel effect, extrafocal radiation and scattered radiation from the KAP meter. The deviations between the calibration factors were as large as for collimator apertures of and distances from the source of 50 - 160 cm. The uncertainty in the calibration factor using the precise method was carefully evaluated and the expanded relative uncertainty estimated to be with a confidence level of 95%.

  • 58. Lillhök, Jan Erik
    et al.
    Grindborg, Jan-Erik
    Lindborg, Lennart
    Gudowska, Irena
    Alm-Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Söderberg, Jonas
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik.
    Kopec, M
    Medin, Joakim
    Nanodosimetry in a clinical neutron therapy beam using the variance-covariance method and Monte Carlo simulations2007Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 52, nr 16, s. 4953-4966Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanodosimetric single-event distributions or their mean values may contribute to a better understanding of how radiation induced biological damages are produced. They may also provide means for radiation quality characterization in therapy beams. Experimental nanodosimetry is however technically challenging and Monte Carlo simulations are valuable as a complementary tool for such investigations. The dose-mean lineal energy was determined in a therapeutic p(65)+Be neutron beam and in a 60Co γ beam using low-pressure gas detectors and the variance-covariance method. The neutron beam was simulated using the condensed history Monte Carlo codes MCNPX and SHIELD-HIT. The dose-mean lineal energy was calculated using the simulated dose and fluence spectra together with published data from track-structure simulations. A comparison between simulated and measured results revealed some systematic differences and different dependencies on the simulated object size. The results show that both experimental and theoretical approaches are needed for an accurate dosimetry in the nanometer region. In line with previously reported results, the dose-mean lineal energy determined at 10 nm was shown to be related to clinical RBE values in the neutron beam and in a simulated 175 MeV proton beam as well. © 2007 IOP Publishing Ltd.

  • 59.
    Lindström, J
    et al.
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Radiofysik.
    Alm Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    A simple model for estimating the particle size dependence of absolut afficienty of fluoroscent screens.1999Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 44, s. 1353-1367Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 60.
    Lindström, Jan
    et al.
    Radiation Physics Department, Borås Hospital, Borås.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    A simple model for estimating the particle size dependence of absolute efficiency of fluorescent screens1999Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 44, nr 5, s. 1353-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The absolute efficiency of a phosphor screen is the ratio of the light energy per unit area at the screen surface to the incident x-ray energy fluence. Particle size is a critical factor in determining the absolute efficiency, but in most models its influence is not accounted for. To allow derivation of the particle size dependence, a model is proposed that describes the optical properties of the screen by means of a single parameter, the light extinction factor, xi, and assumes that the intrinsic efficiency (light energy/energy imparted to the phosphor material) is independent of particle size. The value of xi depends on the type of screen (phosphor, reflective backing, coating and binder) and has to be determined from measurements on at least two screens with known particle size and thickness. The absolute efficiency can then be calculated for an extended range of particle sizes and/or screen thicknesses. To test the model, experimental data from the literature were used to derive values of xi for screens of La2O2S:Tb, LaOBr:Tm and ZnCdS:Ag. The extinction factor was found to vary between -6 and +20%. The non-physical negative value for xi, found from one set of experiments on La2O2S:Tb screens, may be explained as resulting from a lack of accurate knowledge of the actual tube potential, influencing calculated values of the energy imparted to the screen. The results are promising but further well-controlled experiments (including improved dosimetric calculations to account forescape of K-radiation from the screen) are needed to confirm the model.

  • 61.
    Lindström, Jan
    et al.
    Karolinska Univ. Hospital, Sweden.
    Hulthén, Markus
    Karolinska Univ. Hospital, Sweden.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Optimizing two radioluminescence based quality assurance devices for diagnostic radiology utilizing a simple model2014Ingår i: Medical Imaging 2014: Physics of Medical Imaging / [ed] Bruce R. Whiting; Christoph Hoeschen, SPIE - International Society for Optical Engineering, 2014, Vol. 9033, s. 90333R-1-90333R-15Konferensbidrag (Refereegranskat)
    Abstract [en]

    The extrinsic (absolute) efficiency of a phosphor is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. A model described in earlier work has shown that by knowing the intrinsic efficiency, the particle size, the thickness and the light extinction factor ξ, it is possible to deduce the extrinsic efficiency for an extended range of particle sizes and layer thicknesses for a given design. The model has been tested on Gd 2O2S:Tb and ZnS:Cu fluorescent layers utilized in two quality assurance devices, respectively, aimed for the assessment of light field and radiation field congruence in diagnostic radiology. The first unit is an established device based on both fluorescence and phosphorescence containing an x-ray sensitive phosphor (ZnS:Cu) screen comprising a long afterglow. Uncertainty in field edge position is estimated to 0.8 mm (k=2). The second unit is under development and based on a linear CCD sensor which is sensitized to x-rays by applying a Gd 2O2S:Tb scintillator. The field profiles and the corresponding edge location are then obtained and compared. Uncertainty in field edge location is estimated to

    0.1 mm (k=2). The properties of the radioluminescent layers are essential for the functionality of the devices and have been optimized utilizing the previously developed and verified model. A theoretical description of the maximization of phosphorescence is also briefly discussed as well as an interesting finding encountered during the development processes: focal spot wandering. The oversimplistic physical assumptions made in the radioluminescence model have not been found to lead the optimizing process astray. The obtained functionality is believed to be adequate within their respective limitations for both devices.

  • 62.
    Magnusson, Maria
    et al.
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Region Östergötland, Diagnostikcentrum, Medicinsk strålningsfysik.
    Björnfot, Magnus
    Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Diagnostikcentrum, Medicinsk strålningsfysik.
    Carlsson Tedgren, Åsa
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Karolinska Univ, Sweden.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Diagnostikcentrum, Medicinsk strålningsfysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    DIRA-3D-a model-based iterative algorithm for accurate dual-energy dual-source 3D helical CT2019Ingår i: BIOMEDICAL PHYSICS and ENGINEERING EXPRESS, ISSN 2057-1976, Vol. 5, nr 6, artikel-id UNSP 065005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantitative dual-energy computed tomography may improve the accuracy of treatment planning in radiation therapy. Of special interest are algorithms that can estimate material composition of the imaged object. One example of such an algorithm is the 2D model-based iterative reconstruction algorithm DIRA. The aim of this work is to extend this algorithm to 3D so that it can be used with cone-beams and helical scanning. In the new algorithm, the parallel FBP method was replaced with the approximate 3D FBP-based PI-method. Its performance was tested using a mathematical phantom consisting of six ellipsoids. The algorithm substantially reduced the beam-hardening artefact and the artefacts caused by approximate reconstruction after six iterations. Compared to Alvarez-Macovskis base material decomposition, DIRA-3D does not require geometrically consistent projections and hence can be used in dual-source CT scanners. Also, it can use several tissue-specific material bases at the same time to represent the imaged object.

  • 63.
    Magnusson, Maria
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Hälsouniversitetet.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Muhammad, Arif
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Determination of  Quantitative Tissue Composition by Iterative Reconstruction on 3D DECT Volumes2011Konferensbidrag (Refereegranskat)
  • 64.
    Magnusson, Maria
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Tekniska högskolan.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Muhammad, Arif
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Iterative Reconstruction for QuantitativeTissue Decomposition in Dual-Energy CT2011Ingår i: Proceedings of the 17th Scandinavian Conference, SCIA 2011, Ystad, Sweden, May 2011. / [ed] Anders Heyden,Fredrik Kahl, Springer Berlin/Heidelberg, 2011, s. 479-488Konferensbidrag (Refereegranskat)
    Abstract [en]

    Quantitative tissue classification using dual-energy CT has the potential to improve accuracy in radiation therapy dose planning as it provides more information about material composition of scanned objects than the currently used methods based on single-energy CT. One problem that hinders successful application of both single-and dualenergy CT is the presence of beam hardening and scatter artifacts in reconstructed data. Current pre-and post-correction methods used for image reconstruction often bias CT numbers and thus limit their applicability for quantitative tissue classification. Here we demonstrate simulation studies with a novel iterative algorithm that decomposes every soft tissue voxel into three base materials: water, protein and adipose. The results demonstrate that beam hardening artifacts can effectively be removed and accurate estimation of mass fractions of all base materials can be achieved. In the future, the algorithm may be developed further to include segmentation of soft and bone tissue and subsequent bone decomposition, extension from 2-D to 3-D and scatter correction.

  • 65.
    Malusek, Aleksandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Larsson, J. Peter
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Monte Carlo study of the dependence of the KAP-meter calibration coefficient on beam aperture, X-ray tube voltage, and reference plane2007Ingår i: Physics in medicine and biology, ISSN 0031-9155, Vol. 52, nr 4, s. 1157-1170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Monte Carlo method was used to study the dependence of the calibration coefficient on the tube voltage, beam aperture and reference plane in simplified over-couch geometries modelling VacuTec's type 70157 KAP-meter both with and without an additional filter. The MCNP5 code was used to calculate (i) energy imparted to air cavities of the KAP-meter and (ii) spatial distribution of air collision kerma at entrance and exit planes of the KAP-meter and at a plane close to the patient. From these data, the air kerma area product and calibration coefficient were calculated and their dependence on the tube voltage and beam aperture was analysed. It was found that the variation of the calibration coefficient as a function of tube voltage was up to 40% when the additional filter was used. The additional filter placed closely in front of the KAP-meter decreased the calibration coefficient for the patient plane by about 10% compared to the ideal additional filter. The effect of the beam aperture was small at the patient plane and negligible for the exit plane.

  • 66.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Analysis of the tandem calibration method for kerma area meters vis Monte Carlo simulations2011Ingår i: Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS).  Proceedings of an International Symposium held in Vienna, Austria 9-12 November 2010 (2 Volumes), IAEA , 2011, s. 129-136Konferensbidrag (Refereegranskat)
    Abstract [en]

    The IAEA recommends that uncertainties of dosimetric measurements in diagnostic radiology for risk assessment and quality assurance should be less than 7% on the confidence level of 95%. This accuracy is difficult to achieve with kerma area product (KAP) meters currently used in clinics. The reasons range from the high energy dependence of KAP meters to the wide variety of configurations in which KAP meters are used and calibrated. The tandem calibration method introduced by Pöyry, Komppa and Kosunen in 2005 has the potential to make the calibration procedure simpler and more accurate compared to the traditional beam-area method. In this method, two positions of the reference KAP meter are of interest: (a) a position close to the field KAP meter and (b) a position 20 cm above the couch. In the close position, the distance between the two KAP meters should be at least 30 cm to reduce the effect of back scatter. For the other position, which is recommended for the beam-area calibration method, the distance of 70 cm between the KAP meters was used in this study. The aim of this work was to complement existing experimental data comparing the two configurations with Monte Carlo (MC) simulations. In a geometry consisting of a simplified model of the VacuTec 70157 type KAP meter, the MCNP code was used to simulate the kerma area product, PKA, for the two (close and distant) reference planes. It was found that PKA values for the tube voltage of 40 kV were about 2.5% lower for the distant plane than for the close one. For higher tube voltages, the difference was smaller. The difference was mainly caused by attenuation of the X ray beam in air. Since the problem with high uncertainties in PKA measurements is also caused by the current design of X ray machines, possible solutions are discussed.

  • 67.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Helmrot, Ebba
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Patient-specific kerma-area product as an exposure estimator in computed tomography: the concept and typical values2011Ingår i: IAEA, International Symposium on Standards, Applications and Quality Assurance in Medical Radiation Dosimetry (IDOS). 9-12 november 2010, Vienna, Austria. Book of extended synopses. IAEA-CN-182 / [ed] IAEA, International Atomic Energy Agency, Vienna: IAEA , 2011, s. 83-92Konferensbidrag (Refereegranskat)
    Abstract [en]

    Monitoring of exposure levels in computed tomography is important from the radiation safety point of view. In this article, the concept suggested by Huda X[1]X of using the patient-specific kerma-area product as an exposure estimator is extended by providing both a rigorous definition of this quantity and a method for its evaluation. The method was demonstrated on an axial scan of the standard CT dosimetry head phantom taken with a Siemens Somatom Open CT scanner. The resulting patient-specific kerma-area product was 0.25 Gy cm2 for the x-ray tube voltage of 120 kV, tube current of 100 mA, scanning time of 1 s, and beam width at the iso-center of 1.2 cm.  To implement this method, the CT scanner must be equipped with a KAP meter, and the calculation procedure must be added to the scanner's software. Alternatively, the patient-specific kerma-area product can be calculated by the CT scanner without using a KAP meter. In this case, however, the extra safety feature provided by the direct monitoring of the x-ray beam by the KAP meter is lost.

  • 68.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet.
    Helmrot, Ebba
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Grindborg, J-E
    Swedish Radiat Protect Author, Sweden.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    In-situ calibration of clinical built-in KAP meters with traceability to a primary standard using a reference KAP meter2014Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, nr 23, s. 7195-7210Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The air kerma-area product (KAP) is used for settings of diagnostic reference levels. The International Atomic Energy Agency (IAEA) recommends that doses in diagnostic radiology (including the KAP values) be estimated with an accuracy of at least +/- 7% (k = 2). Industry standards defined by the International Electrotechnical Commission (IEC) specify that the uncertainty of KAP meter measurements should be less than +/- 25% (k = 2). Medical physicists willing to comply with the IAEAs recommendation need to apply correction factors to KAP values reported by x-ray units. The aim of this work is to present and evaluate a calibration method for built-in KAP meters on clinical x-ray units. The method is based on (i) a tandem calibration method, which uses a reference KAP meter calibrated to measure the incident radiation, (ii) measurements using an energy-independent ionization chamber to correct for the energy dependence of the reference KAP meter, and (iii) Monte Carlo simulations of the beam quality correction factors that correct for differences between beam qualities at a standard laboratory and the clinic. The method was applied to the KAP meter in a Siemens Aristos FX plus unit. It was found that values reported by the built-in KAP meter differed from the more accurate values measured by the reference KAP meter by more than 25% for high tube voltages (more than 140 kV) and heavily filtered beams (0.3 mm Cu). Associated uncertainties were too high to claim that the IECs limit of 25% was exceeded. Nevertheless the differences were high enough to justify the need for a more accurate calibration of built-in KAP meters.

  • 69.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Karlsson, Mattias
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet.
    Magnusson, Maria
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska högskolan.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    The potential of dual-energy computed tomography for quantitative decomposition of soft tissues to water, protein and lipid in brachytherapy2013Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, nr 4, s. 771-785Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dosimetric accuracy of radiation treatment planning in brachytherapy depends on knowledge of tissue composition. It has been speculated that soft tissues can be decomposed to water, lipid and protein. The aim of our work is to evaluate the accuracy of such tissue decomposition. Selected abdominal soft tissues, whose average elemental compositions were taken from literature, were decomposed using dual energy computed tomography to water, lipid and protein via the three-material decomposition method. The quality of the decomposition was assessed using relative differences between (i) mass energy absorption and (ii) mass energy attenuation coefficients of the analyzed and approximated tissues. It was found that the relative differences were less than 2% for photon energies larger than 10 keV. The differences were notably smaller than the ones for water as the transport and dose scoring medium. The choice of the water, protein and lipid triplet resulted in negative elemental mass fractions for some analyzed tissues. As negative elemental mass fractions cannot be used in general purpose particle transport computer codes using the Monte Carlo method, other triplets should be used for the decomposition. These triplets may further improve the accuracy of the approximation as the differences were mainly caused by the lack of high-Z materials in the water, protein and lipid triplet.

  • 70.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Magnusson, Maria
    Linköpings universitet, Institutionen för systemteknik, Datorseende. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    A model-based iterative reconstruction algorithm DIRA using patient-specific tissue classification via DECT for improved quantitative CT in dose planning2017Ingår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, nr 6, s. 2345-2357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: To develop and evaluate-in a proof-of-concept configuration-a novel iterative reconstruction algorithm (DIRA) for quantitative determination of elemental composition of patient tissues for application to brachytherapy with low energy (amp;lt; 50 keV) photons and proton therapy. Methods: DIRA was designed as a model-based iterative reconstruction algorithm, which uses filtered backprojection, automatic segmentation and multimaterial tissue decomposition. The evaluation was done for a phantom derived from the voxelized ICRP 110 male phantom. Soft tissues were decomposed to the lipid, protein and water triplet, bones were decomposed to the compact bone and bone marrow doublet. Projections were derived using the Drasim simulation code for an axial scanning configuration resembling a typical DECT (dual-energy CT) scanner with 80 kV and Sn140 kV x-ray spectra. The iterative loop produced mono-energetic images at 50 and 88 keV without beam hardening artifacts. Different noise levels were considered: no noise, a typical noise level in diagnostic imaging and reduced noise level corresponding to tenfold higher doses. An uncertainty analysis of the results was performed using type A and B evaluations. The two approaches were compared. Results: Linear attenuation coefficients averaged over a region were obtained with relative errors less than 0.5% for all evaluated regions. Errors in average mass fractions of the three-material decomposition were less than 0.04 for no noise and reduced noise levels and less than 0.11 for the typical noise level. Mass fractions of individual pixels were strongly affected by noise, which slightly increased after the first iteration but subsequently stabilized. Estimates of uncertainties in mass fractions provided by the type B evaluation differed from the type A estimates by less than 1.5% for most cases. The algorithm was fast, the results converged after 5 iterations. The algorithmic complexity of forward polyenergetic projection calculation was much reduced by using material doublets and triplets. Conclusions: The simulations indicated that DIRA is capable of determining elemental composition of tissues, which are needed in brachytherapy with low energy (amp;lt; 50 keV) photons and proton therapy. The algorithm provided quantitative monoenergetic images with beam hardening artifacts removed. Its convergence was fast, image sharpness expressed via the modulation transfer function was maintained, and image noise did not increase with the number of iterations. c 2017 American Association of Physicists in Medicine

  • 71.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet.
    Magnusson, Maria
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Westin, Robin
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Prostate tissue decomposition via DECT using the modelbased iterative image reconstruction algorithm DIRA2014Ingår i: Medical Imaging 2014: Physics of Medical Imaging / [ed] Bruce R. Whiting; Christoph Hoeschen; Despina Kontos, SPIE - International Society for Optical Engineering, 2014, Vol. 9033, nr 90333H, s. Art.nr. 90333H-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Better knowledge of elemental composition of patient tissues may improve the accuracy of absorbed dose delivery in brachytherapy. Deficiencies of water-based protocols have been recognized and work is ongoing to implement patient-specific radiation treatment protocols. A model based iterative image reconstruction algorithm DIRA has been developed by the authors to automatically decompose patient tissues to two or three base components via dual-energy computed tomography. Performance of an updated version of DIRA was evaluated for the determination of prostate calcification. A computer simulation using an anthropomorphic phantom showed that the mass fraction of calcium in the prostate tissue was determined with accuracy better than 9%. The calculated mass fraction was little affected by the choice of the material triplet for the surrounding soft tissue. Relative differences between true and approximated values of linear attenuation coefficient and mass energy absorption coefficient for the prostate tissue were less than 6% for photon energies from 1 keV to 2 MeV. The results indicate that DIRA has the potential to improve the accuracy of dose delivery in brachytherapy despite the fact that base material triplets only approximate surrounding soft tissues.

  • 72.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Magnusson Seger, Maria
    Linköpings universitet, Institutionen för systemteknik, Bildbehandling. Linköpings universitet, Tekniska högskolan.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Effect of scatter on reconstructed image quality in cone beam CT: evaluation of a scatterreduction optimization function2005Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 114, nr 1-3, s. 337-340Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of scatter on reconstructed image quality in conebeam computed tomography was investigated and a function whichcan be used in scatter-reduction optimisation tasks was tested.Projections were calculated using the Monte Carlo method inan axially symmetric cone beam geometry consisting of a pointsource, water phantom and a single row of detector elements.Image reconstruction was performed using the filtered backprojectionmethod. Image quality was assessed by the L2-norm-based differencerelative to a reference image derived from (1) weighted linearattenuation coefficients and (2) projections by primary photons.It was found that the former function was strongly affectedby the beam hardening artefact and did not properly reflectthe amount of scatter but the latter function increased withincreasing beam width, was higher for the larger phantom andexhibited properties which made it a good candidate for scatter-reductionoptimisation tasks using polyenergetic beams.

  • 73.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Medicinska fakulteten.
    ACCURATE KAP METER CALIBRATION AS A PREREQUISITE FOR OPTIMISATION IN PROJECTION RADIOGRAPHY2016Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, nr 1-4, s. 353-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modern X-ray units register the air kerma–area product, PKA, with a built-in KAP meter. Some KAP meters show an energydependent bias comparable with the maximum uncertainty articulated by the IEC (25 %), adversely affecting dose-optimisation processes. To correct for the bias, a reference KAP meter calibrated at a standards laboratory and two calibration methods described here can be used to achieve an uncertainty of <7 % as recommended by IAEA. A computational model of the reference KAP meter is used to calculate beam quality correction factors for transfer of the calibration coefficient at the standards laboratory, Q0, to any beam quality, Q, in the clinic. Alternatively, beam quality corrections are measured with an energy-independent dosemeter via a reference beam quality in the clinic, Q1, to beam quality, Q. Biases up to 35 % of built-in KAP meter readings were noted. Energy-dependent calibration factors are needed for unbiased PKA. Accurate KAP meter calibration as a prerequisite for optimisation in projection radiography.

  • 74.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Calculation of the energy absorption efficiency function of selected detector arrays using the MCNP code2007Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report describes a method for the calculation of the energy absorption efficiency function. It gives a theoretical justification of the method and presents results obtained using the MCNP4C code for (i) an infinite slab, (ii) a detector array without a collimator, and (iii) a detector array with a collimator. Moreover, it discusses an alternative method of scoring of the energy imparted per unit surface area in CTmod. This report is a supplement to the article “CTmod—a toolkit for Monte Carlo simulation of projections including scatter in computed tomography” by A. Malusek, M. Sandborg, and G. Alm Carlsson.

  • 75.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    CTmod: a toolkit for Monte Carlo simulation of projections including scatter in computed tomography2008Ingår i: Computer Methods and Programs in Biomedicine, ISSN 0169-2607, E-ISSN 1872-7565, Vol. 90, nr 2, s. 167-178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The CTmod toolkit is a set of C++ class libraries based on the CERN’s application development framework ROOT. It uses the Monte Carlo method to simulate energy imparted to a CT-scanner detector array. Photons with a given angle–energy distribution are emitted from the X-ray tube approximated by a point source, transported through a phantom, and their contribution to the energy imparted per unit surface area of each detector element is scored. Alternatively, the scored quantity may be the fluence, energy fluence, plane fluence, plane energy fluence, or kerma to air in the center of each detector element. Phantoms are constructed from homogenous solids or voxel arrays via overlapping. Implemented photon interactions (photoelectric effect, coherent scattering, and incoherent scattering) are restricted to the energy range from 10 to 200 keV. Variance reduction techniques include the collision density estimator and survival biasing combined with the Russian roulette. The toolkit has been used to estimate the amount of scatter in cone beam computed tomography and planar radiography.

  • 76.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    CTmod: Mathematical Foundations2007Rapport (Övrigt vetenskapligt)
    Abstract [en]

    CTmod is a set of C++ class libraries primarily designed for the simulation of energy imparted to a CT-scanner detector array using the Monte Carlo method. This report describes mathematical methods and formulas that are used in the code. It is a supplement to the article “CTmod - a toolkit for Monte Carlo simulation of projections including scatter in computed tomography” by A. Malusek, M. Sandborg, and G. Alm Carlsson.

    In this report, random variables are denoted by a hat. For instance ˆx is a random variable and x is its sample. Points in space are denoted by bold capital letters, e.g. P. Directions are denoted by bold small letters, e.g. u. Inconsistencies in the current notation will be corrected in the next update of this report.

  • 77.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Simulation of scatter in cone beam CT – effects on projection image quality2003Ingår i: Proceedings of SPIE 5030: Medical Imaging 2003: Physics of Medical Imaging, Vol. 5030, s. 740-751Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cone-beam computed tomography (CT) projections were calculated by the Monte Carlo method for two cylindrical water phantoms of different sizes and for an antropomorphic voxel phantom with and without the presence of an anti-scatter grid. The scatter-to-primary ratio (SPR) was evaluated for each projection and the dependence of the amount of scattered radiation on the phantom size, cone beam size, photon energy, and antiscatter grid was investigated. It was found that the amount of scattered radiation is a slowly varying function of position in the image plane whose values, depending on configuration parameters, may cover a range of several magnitudes. The SPR reflects changes in the amount of primary photons and may reach values around 5 for large phantoms, wide beams and 120 kV spectrum or even higher values for low energy photons.

  • 78.
    Malusek, Alexandr
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Validation of the CTmod toolkit2007Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report is a supplement to the article “CTmod—a toolkit for Monte Carlo simulation of projections including scatter in computed tomography” by A. Malusek, M. Sandborg, and G. Alm Carlsson. It describes methods that were used to validate the CTmod toolkit. Here, we adopt the terminology used in and: Verification is a process of determining whether or not the software is coded correctly and conforms to the specified requirements. Validation is a process of evaluating software to ensure compliance with physical applicability to the process being modelled. Validation of a code would consist of comparing it with known analytical solutions or against an already validated computer code, or could include benchmarking the code against relevant experimental data.

    CTmod is a toolkit implemented as a C++ class libray. A user is supposed to write a main program which uses classes from the toolkit. The main program is then compiled to create an executable. In this report, we tested two executables (ctmod1 and ctmod2) created this way. In chapter 2, scatter-to-primary ratios of air collision kerma calculated using ctmod1 are compared to data published in literature. In chapter 3, primary and scatter projections calculated using ctmod2 are compared to data calculated using the MCNP5 code. Though not related to the validation, we also report speeds of ctmod1 and ctmod2 as these were often requested from us.

  • 79. McVey, Graham
    et al.
    Sandborg, Michael
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Dance, David
    Alm Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    A study and optimization of lumbar spine X-ray imaging systems2003Ingår i: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 76, nr 903, s. 177-188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Monte Carlo program has been developed that incorporates a voxel phantom of an adult patient in a model of the complete X-ray imaging system, including the anti-scatter grid and screen-film receptor. This allows the realistic estimation of patient dose and the corresponding image (optical density map) for a wide range of equipment configurations. This paper focuses on the application of the program to lumbar spine anteroposterior and lateral screen-film examinations. The program has been applied to study the variation of physical image quality measures and effective dose for changing system parameters such as tube voltage, grid design and screen-film system speed. These variations form the basis for optimization of these system parameters. In our approach to optimization, the best systems are those that can match (or come close to) the calculated image quality measure of systems preferred in a recent European clinical trial, but with lower patient dose. The largest dose savings found were 21% for a 400 speed class system with a grid having a strip density of 40 cm-1 and a grid ratio of 16. A further dose saving of 13% was possible when a 600 speed class system was employed. The best systems found from the optimization correspond to those recommended by the European Commission guidelines on image quality criteria for diagnostic radiographic images.

  • 80. Moores, B
    et al.
    Mattsson, S
    Månsson, LG
    Panzer, W
    Regulla, D
    Dance, D
    Alm-Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Verdun, F
    Buhr, E
    Hoeschen, C
    RADIUS - Closing the circle on the assessment of imaging performance2005Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, nr 1-3, s. 450-457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The RADIUS (Radiological Imaging Unification Strategy) project addresses the assessment of image quality in terms of both physical and clinically relevant measures. The aim is to unify our understanding of both types of measure as well as the numerous underlying factors that play a key role in the assessments of imaging performance. In this way it is expected to provide a solid basis for the improvement in radiological safety management, where not only radiation risks are considered but also diagnostic risks of incorrect clinical outcomes (i.e. false positive/false negative). The project has applied a variety of relevant experimental and theoretical methods to this problem, which is generic to medical imaging as a whole. Digital radiography of the chest and the breast has been employed as the clinical imaging domain vehicles for the study. The project addressed the problem from the following directions: role and relevance of pathology, human observer studies including receiver operating characteristics, image quality criteria analysis, structural noise analysis, physical measurements on clinical images, physical measurements on imaging system, modelling of imaging system, modelling of visual processes, modelling of doses delivered and IT-based scientific support strategies. This paper presents an overview of the main outcomes from this project and highlights how the research outcomes actually apply to the real world. In particular, attention will be focused on new and original findings and methods and techniques that have been developed within the framework of the project. The relevance of the project's outcomes to future European research will also be presented. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 81.
    Mukhopadhyay, Nitai D
    et al.
    Virginia Commonwealth Univ, Richmond, USA.
    Sampson, Andrew J
    Virginia Commonwealth Univ, Richmond, USA.
    Deniz, Daniel
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Williamson, Jeffrey
    Virginia Commonwealth Univ, Richmond, USA.
    Malusek, Alexandr
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Estimating statistical uncertainty of Monte Carlo efficiency-gain in the context of a correlated sampling Monte Carlo code for brachytherapy treatment planning with non-normal dose distribution2012Ingår i: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 70, nr 1, s. 315-323Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Correlated sampling Monte Carlo methods can shorten computing times in brachytherapy treatment planning. Monte Carlo efficiency is typically estimated via efficiency gain, defined as the reduction in computing time by correlated sampling relative to conventional Monte Carlo methods when equal statistical uncertainties have been achieved. The determination of the efficiency gain uncertainty arising from random effects, however, is not a straightforward task specially when the error distribution is non-normal. The purpose of this study is to evaluate the applicability of the F distribution and standardized uncertainty propagation methods (widely used in metrology to estimate uncertainty of physical measurements) for predicting confidence intervals about efficiency gain estimates derived from single Monte Carlo runs using fixed-collision correlated sampling in a simplified brachytherapy geometry. A bootstrap based algorithm was used to simulate the probability distribution of the efficiency gain estimates and the shortest 95% confidence interval was estimated from this distribution. It was found that the corresponding relative uncertainty was as large as 37% for this particular problem. The uncertainty propagation framework predicted confidence intervals reasonably well; however its main disadvantage was that uncertainties of input quantities had to be calculated in a separate run via a Monte Carlo method. The F distribution noticeably underestimated the confidence interval. These discrepancies were influenced by several photons with large statistical weights which made extremely large contributions to the scored absorbed dose difference. The mechanism of acquiring high statistical weights in the fixed-collision correlated sampling method was explained and a mitigation strategy was proposed.

  • 82.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Bake, Björn
    Sahlgrenska universitetssjukhuset, Göteborg.
    Jacobsson, Lars
    Göteborgs universitet, Göteborg.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Evaluation of reconstruction techniques for lung single photon emission tomography: A Monte Carlo study2007Ingår i: Nuclear medicine communications, ISSN 0143-3636, E-ISSN 1473-5628, Vol. 28, nr 12, s. 929-936Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND: In studies of the distribution of lung function, the image quality of lung single photon emission computed tomography (SPECT) is important and one factor influencing it is the reconstruction algorithm. AIM: To systematically evaluate ordered subsets expectation maximization (OSEM) and compare it with filtered back-projection (FBP) for lung SPECT with Tc. METHODS: The evaluation of the number of iterations used in OSEM was based on the image quality parameter contrast. The comparison between OSEM and FBP was based on trade-off plots between statistical noise and spatial resolution for different filter parameters, collimators and count-levels. A Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing two sets of activity: one with a homogeneous activity distribution within the lungs and the other with superposed high- and low-activity objects. Statistical noise in the reconstructed images was calculated as the coefficient of variation (CV) and spatial resolution as full width at half-maximum (FWHM). RESULTS: For the configuration studied, the OSEM reconstruction in combination with post-filtering should be used in lung SPECT studies with at least 60 MLEM equivalent iterations. Compared to FBP the spatial resolution was improved by about 1 mm. For a constant level of CV, a four-fold increase in count level resulted in an increased resolution of about 2 mm. Spatial resolution and cut-off frequency depends on what value of noise in the image is acceptable also increased by using a low-energy, high-resolution collimator for CV values above 3%. The choice of noise-reducing filter and cut-off frequency depends on what value of noise in the image is acceptable.

  • 83.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Olsson, Anna
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Gustafsson, Agneta
    Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Optimisation of quantitative lung SPECT applied to mild COPD: a software phantom simulation study2015Ingår i: EJNMMI research, ISSN 2191-219X, Vol. 5, nr 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND: The amount of inhomogeneities in a (99m)Tc Technegas single-photon emission computed tomography (SPECT) lung image, caused by reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), is correlated to disease advancement. A quantitative analysis method, the CVT method, measuring these inhomogeneities was proposed in earlier work. To detect mild COPD, which is a difficult task, optimised parameter values are needed.

    METHODS: In this work, the CVT method was optimised with respect to the parameter values of acquisition, reconstruction and analysis. The ordered subset expectation maximisation (OSEM) algorithm was used for reconstructing the lung SPECT images. As a first step towards clinical application of the CVT method in detecting mild COPD, this study was based on simulated SPECT images of an advanced anthropomorphic lung software phantom including respiratory and cardiac motion, where the mild COPD lung had an overall ventilation reduction of 5%.

    RESULTS: The best separation between healthy and mild COPD lung images as determined using the CVT measure of ventilation inhomogeneity and 125 MBq (99m)Tc was obtained using a low-energy high-resolution collimator (LEHR) and a power 6 Butterworth post-filter with a cutoff frequency of 0.6 to 0.7 cm(-1). Sixty-four reconstruction updates and a small kernel size should be used when the whole lung is analysed, and for the reduced lung a greater number of updates and a larger kernel size are needed.

    CONCLUSIONS: A LEHR collimator and 125 (99m)Tc MBq together with an optimal combination of cutoff frequency, number of updates and kernel size, gave the best result. Suboptimal selections of either cutoff frequency, number of updates and kernel size will reduce the imaging system's ability to detect mild COPD in the lung phantom.

  • 84.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Olsson, Anna
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Optimisation of quantitative lung SPECT applied to mild COPD: a Monte Carlo-based analysis2014Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The amount of inhomogeneities in a single photon emission computed tomography (SPECT) lung image, caused by reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), is correlated to disease advancement. A quantitative analysis method, the CVT-method, measuring these inhomogeneities was proposed in earlier work (Norberg et al., 2013). To detect mild COPD, which is a difficult task, optimized parameter values are needed. In this work, the CVT-method was optimized with respect to the parameter values of acquisition, reconstruction and analysis. The ordered subset expectation maximization (OSEM) algorithm was used for reconstructing the lung SPECT images. As a first step towards clinical application of the CVT-method in detecting mild COPD, this study was based on simulated SPECT images of an advanced anthropomorphic lung phantom including respiratory and cardiac motion, where the mild COPD lung had an overall ventilation reduction of 5%. The largest separation between healthy and mild COPD lung images as determined using the CVT-measure of ventilation inhomogeneity and 125 MBq 99mTc was obtained using a low-energy high-resolution collimator and a Butterworth postfilter with a cut-off frequency of 0.6-0.7 cm-1. Sixty-four reconstruction updates should be used when the whole lung is analysed and for the reduced lung a greater number of updates is needed.

  • 85.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Persson, H Lennart
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Lungmedicinska kliniken US.
    Schmekel, Birgitta
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för kardiovaskulär medicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Wahlin, Karl
    Linköpings universitet, Institutionen för datavetenskap, Statistik. Linköpings universitet, Filosofiska fakulteten.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Does quantitative lung SPECT detect lung abnormalities earlier than lung function tests?: Results of a pilot study2014Ingår i: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 4, nr 39, s. 1-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Heterogeneous ventilation in lungs of allergic individuals, cigarette smokers, asthmatics and chronic obstructive pulmonary disease (COPD) patients has been demonstrated using imaging modalities such as PET, MR and SPECT. These individuals suffer from narrow and/or closed airways to various extents. By calculating regional heterogeneity in lung ventilation SPECT images as the coefficient of variation (CV) in small elements of the lung, heterogeneity maps and CV-frequency curves can be generated and used to quantitatively measure heterogeneity. This work explores the potential to use such measurements to detect mild ventilation heterogeneities in lung healthy subjects.

    Method: Fourteen healthy subjects without documented lung disease or respiratory symptoms, and two patients with documented airway disease, inhaled on average approximately 90 MBq 99mTc-Technegas immediately prior to the 20 min SPECT acquisition. Variation in activity uptake between subjects was compensated for in resulting CV values. The area under the compensated CV frequency curve (AUC), for CV values greater than a threshold value CVT, AUC(CV> CVT), was used as the measure of ventilation heterogeneity.

    Results: Patients with lung function abnormalities, according to lung function tests, generated higher AUC(CV>20%) values compared to healthy subjects (p=0.006). Strong linear correlations with the AUC(CV>20%) values were found for age (p=0.006) and height (p=0.001). These demonstrated that ventilation heterogeneities increased with age and that they depend on lung size. Strong linear correlations were found for the lung function value related to indices of airway closure/air trapping, RV/TLC (p=0.009), and DLCOc (p=0.009), a value partly related to supposed ventilation/perfusion mismatch. These findings support the association between conventional lung function tests and the AUC(CV>20%) value.

    Conclusions: Among the healthy subjects there is a group with increased AUC(CV>20%) values, but with normal lung function tests, which implies that it might be possible to differentiate ventilation heterogeneities earlier in a disease process than by lung function tests.

  • 86.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Persson, Hans Lennart
    Linköpings universitet, Institutionen för medicin och hälsa, Lungmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Lungmedicinska kliniken US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Bake, Björn
    Sahlgrenska Academy at University of Gothenburg.
    Kentson, Magnus
    Ryhov Hospital.
    Sandborg, Michael
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    Quantitative lung SPECT applied on simulated early COPD and humans with advanced COPD2013Ingår i: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 3, nr 28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND:Reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), reflected as inhomogeneities in the single-photon emission computed tomography (SPECT) lung image, is correlated to disease advancement. An analysis method for measuring these inhomogeneities is proposed in this work. The first aim was to develop a quantitative analysis method that could discriminate between Monte Carlo simulated normal and COPD lung SPECT images. A second aim was to evaluate the ability of the present method to discriminate between human subjects with advanced COPD and healthy volunteers.

    METHODS:In the simulated COPD study, different activity distributions in the lungs were created to mimic the healthy lung (normal) and different levels of COPD. Gamma camera projections were Monte Carlo simulated, representing clinically acquired projections of a patient who had inhaled 125 MBq 99mTc-Technegas followed by a 10-min SPECT examination. Reconstructions were made with iterative ordered subset expectation maximisation. The coefficient of variance (CV) was calculated for small overlapping volumes covering the 3D reconstructed activity distribution. A CV threshold value (CVT) was calculated as the modal value of the CV distribution of the simulated normal. The area under the distribution curve (AUC), for CV values greater than CVT, AUC(CVT), was then calculated. Moreover, five patients with advanced emphysema and five healthy volunteers inhaled approximately 75 MBq 99mTc-Technegas immediately before the 20-min SPECT acquisition. In the human study, CVT was based on the mean CV distribution of the five healthy volunteers.

    RESULTS:A significant difference (p < 0.001) was found between the Monte-Carlo simulated normal and COPD lung SPECT examinations. The present method identified a total reduction of ventilation of approximately 5%, not visible to the human eye in the reconstructed image. In humans the same method clearly discriminated between the five healthy volunteers and five patients with advanced COPD (p < 0.05).

    CONCLUSIONS:While our results are promising, the potential of the AUC(CVT) method to detect less advanced COPD in patients needs further clinical studies.

  • 87.
    Norberg, Pernilla
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Sandborg, Michael
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Alm Carlsson, Gudrun
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Radiofysikavdelningen US.
    Persson, Lennart
    Linköpings universitet, Institutionen för medicin och hälsa, Lungmedicin. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Centrum för kirurgi, ortopedi och cancervård, Lungmedicinska kliniken US.
    Bake, Björn
    Avdelningen för intermedicin, Institutionen för medicin, Sahlgrenska Akademin vid Göteborgs Universitet, Göteborg.
    Kentson, Magnus
    Avdelningen för Lungmedicin, Länssjukhuset Ryhov, Jönköping .
    Quantitative lung-SPECT applied on simulated early COPD and humans with advanced COPD2012Konferensbidrag (Övrigt vetenskapligt)
  • 88.
    Olsson, Anna
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Ärlig, Åsa
    County Hospital Ryhov, Jönköping.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Gustafsson, Agnetha
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Evaluation of reconstruction techniques in regional cerebral blood flow SPECT using trade-off plots: A Monte Carlo study2007Ingår i: Nuclear medicine communications, ISSN 0143-3636, E-ISSN 1473-5628, Vol. 28, nr 9, s. 719-725Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND AND AIM: The image quality of single photon emission computed tomography (SPECT) depends on the reconstruction algorithm used. The purpose of the present study was to evaluate parameters in ordered subset expectation maximization (OSEM) and to compare systematically with filtered back-projection (FBP) for reconstruction of regional cerebral blood flow (rCBF) SPECT, incorporating attenuation and scatter correction. METHODS: The evaluation was based on the trade-off between contrast recovery and statistical noise using different sizes of subsets, number of iterations and filter parameters. Monte Carlo simulated SPECT studies of a digital human brain phantom were used. The contrast recovery was calculated as measured contrast divided by true contrast. Statistical noise in the reconstructed images was calculated as the coefficient of variation in pixel values. RESULTS: A constant contrast level was reached above 195 equivalent maximum likelihood expectation maximization iterations. The choice of subset size was not crucial as long as there were > or = 2 projections per subset. The OSEM reconstruction was found to give 5-14% higher contrast recovery than FBP for all clinically relevant noise levels in rCBF SPECT. The Butterworth filter, power 6, achieved the highest stable contrast recovery level at all clinically relevant noise levels. The cut-off frequency should be chosen according to the noise level accepted in the image. CONCLUSION: Trade-off plots are shown to be a practical way of deciding the number of iterations and subset size for the OSEM reconstruction and can be used for other examination types in nuclear medicine.

  • 89.
    Olsson, Sara
    et al.
    Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Bagherian, Shahrbanou
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemisk Fysik. Linköpings universitet, Hälsouniversitetet.
    Lund, Eva
    Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Lund, Anders
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemisk Fysik. Linköpings universitet, Tekniska högskolan.
    Ammonium tartrate as an ESR dosimeter material1999Ingår i: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 50, nr 5, s. 955-965Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study is one step in the search for an ESR dosimeter material with a higher signal intensity than the commonly used l-α-alanine, to be useful in the clinical dose range (approximately 0.1–20 Gy). The substance ammonium tartrate was found and investigated regarding signal intensity, radical stability, dose response and dose resolution. The ESR signal intensity of ammonium tartrate was shown to be more than twice the intensity of the alanine signal. The data indicate that an unstable radiation induced radical contributes to the ESR signal initially; after a couple of hours it has converted to a secondary radical which has a decay slow enough to be considered stable during the first two weeks after irradiation. Ammonium tartrate has a linear dose response in the investigated range of 0.5–4000 Gy and a dose resolution of 0.1 Gy at the 0.5 Gy level where, as a comparison, the corresponding value for alanine is 0.3 Gy. We thus find the substance suitable for clinical dosimetry.

  • 90.
    Pernicka, Frantisek
    et al.
    Vienna.
    Alm Carlsson, Gudrun
    Linköpings universitet, Hälsouniversitetet. Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Dance, David
    London.
    DeWerd, Larry
    Wisconsin.
    Kramer, Hans-Michael
    Braunschweig.
    Ng, Kwan-Hong
    Kuala Lumpur.
    Development of an internationl code of practice for dosimetry in x-ray diagnostic radiology.2001Ingår i: IAEA (International Atomic Energy Agency), ISSN 1563-0153, Vol. 1, s. 93-98Artikel i tidskrift (Övrigt vetenskapligt)
  • 91.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Influence on X-ray energy spectrum, contrasting detail and detector on the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) in projection radiography1992Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 7, nr 6, s. 1245-1263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A lower limit to patient irradiation in diagnostic radiology is set by the fundamental stochastics of the energy imparted to the image receptor (quantum noise). Image quality is investigated and expressed in terms of the signal-to-noise ratio due to quantum noise. The Monte Carlo method is used to calculate signal-to-noise ratios (SNRDelta S) and detective quantum efficiencies (DQEDelta S) in imaging thin contrasting details of air, fat, bone and iodine within a water phantom using X-ray spectra (40-140 kV) and detectors of CsI, BaFCl and Gd2O2S. The atomic composition of the contrasting detail influences considerably the values of SNRDelta S due to the different modulations of the energy spectra of primary photons passing beside and through the contrasting detail. By matching the absorption edges of the contrasting detail and the detector, a partially absorbing detector may be more efficient (yield higher SNRDelta S) than a totally absorbing one; this is demonstrated for the case of detecting an iodine detail using a CsI detector. The degradation of SNRDelta S and DQEDelta S due to scatter is larger when the detector is operated in the photon counting compared to in the energy integrating mode and for partially absorbing compared to totally absorbing detectors.

  • 92.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och vård, Radiofysik. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen.
    Jämförelse mellan ett niobfilter (NIOBI-X) och konventionell filtrering vid skärmfilm radiografi: Inverkan på primärspektrum, kontrast, rörbelastning och strålrisk1990Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Optimering av information till strålrisk inom diagnostisk radiologi innebär att finna den.metod att framställa en bild, innehållande den nödvändiga informationen (bildkvaliteten), som ger lägsta strålrisk för patienten. Valet av fotonenergispektrum är en betydelsefull parameter vid optimeringen. Olika energispektrum kan erhållas då man varierar rörspänningen, tilläggsfiltermaterial och filtertjocklek. Av de fundamentala bildkvalitetsparamerarna kontrast, skärpa och brus är, vid konventionell skärm-film radiografi, kontrast och skärpa de viktigaste. De påverkas båda, men framförallt kontrasten, av energispektrum, dvs. rörspänningen och tilläggsfiltrets material och tjocklek.

  • 93.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Carlsson, Carl
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Choice of optimal energy spectra in diagnostic radiology: an analysis based on calcu­lated signal-to-noise ratios in clinical, partially absorbing detectors1989Ingår i: British Institute of Radiology, Report 20, London: British Institute of Radiology, , 1989, s. 141-143Konferensbidrag (Refereegranskat)
  • 94.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Dance, David
    n/a.
    Comparison of different materials for test phantoms in diagnostic radiology1993Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 49, nr 1, s. 345-347Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of test phantoms in diagnostic radiology is a well established practice in image quality control. Here Monte Carlo methods are used for comparing different phantom materials (water, Lucite, polystyrene, paraffin wax, Mylar, Mix-D, M3, Alderson muscle B and A-150) relative to soft tissue with regard to different physical quantities such as contrast and mean absorbed dose in the phantom. The results for each material are derived as the equivalent thicknesses resulting in the same value of the quantity of interest as a soft tissue phantom of a given thickness, this being varied between 5 and 25 cm. The phantom material yielding the smallest spread of equivalent thicknesses is regarded as the most soft tissue equivalent one. Water, Mix-D and M3 are the materials most equivalent to soft tissue of the phantom materials tested. Paraffin wax, polystyrene and Lucite show a larger spread in equivalent thicknesses.

  • 95.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Carlsson, C. A.
    Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Shaping X-ray spectra with filters in X-ray diagnostics1994Ingår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 32, nr 4, s. 384-390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence on image contrast, tube load and patient mean absorbed dose of different ways of shaping diagnostic X-ray spectra by placing filters in the beam is derived for two radiographic models (abdominal screen-film radiography and intra-oral, dental radiography) using a computational model. The filters are compared at either equal tube load (keeping tube potential constant) or equal contrast (adjusting the tube potential with the different filters), but always at equal energy imparted per unit area to the image receptor. Compared at equal tube load and relative to standard aluminium filtration, reductions in the mean absorbed dose in the patient of 15–25% can be achieved using filters of Cu, Ti, W and Au (increasing the tube load by 30–40% compared with standard aluminium filtration). However, contrast is also reduced by 7%. Compared at equal contrast, the dose reductions are smaller, about 10%. Filters of copper are generally recommended, as are filters of aluminium. The use of bandpass filters (K-edge filters) should be restricted to examinations where the need for substantial variation in tube potential from patient to patient is small. The benefit of using thicker filters than those commonly used today (increasing tube load by factors of 1.4–2.0 compared with no added filter) is small as the dose reduction is most rapid for small initial values of added filters, and the increase in tube load increases steadily with increasing filter thickness.

  • 96.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Christoffersson, Jan-Ove
    n/a.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Almen, Torsten
    n/a.
    Dunce, D A
    n/a.
    The physical performance of different x-ray contrast agents: calculations using a Monte Carlo model of the imaging chain1995Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 40, nr 7, s. 1209-1224Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Monte Carlo computational model of the imaging chain has been used to investigate the performance of X-ray contrast agents with atomic number, Z, 53<or=Z<or=90 with respect to physical image quality descriptors (contrast and signal to noise ratio, SNR) and patient mean absorbed dose. Contrast agents of equal molar concentrations were used within a water slab (simulating the patient). The imaging conditions were chosen to represent adult and paediatric examinations. For all tube potentials studied (40-140 kV), the contrast agents with the highest atomic numbers (bismuth and thorium) gave the highest contrast. In analogue screen-film imaging, several other contrast agents could produce a higher image contrast than iodine in a limited range of tube potentials. This advantage could alternatively be effected as a reduced amount of administered contrast agent, or as a reduced mean absorbed dose in the patient. In digital imaging, a lower mean absorbed dose for a constant SNR than that with iodine can be achieved for ranges of tube potentials and contrast agents. Bismuth and thorium yield a lower dose than iodine at all studied tube potentials. Gadolinium and erbium could alternatively be used at a broad range of tube potentials above 90 kV with a dose penalty of only 5-20%.

  • 97.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Dance, David
    n/a.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Monte Carlo study of grid performance in diagnostic radiology: factors which affect the selection of tube potential and grid ratio1993Ingår i: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 66, s. 1164-1176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Monte Carlo computational model has been developed for the study of the performance of anti-scatter grids in diagnostic radiology. It is used here to estimate the scatter in the image plane from soft tissue phantoms (representing the patient) and to calculate image contrast and the mean absorbed dose in the phantom. Different scattering conditions, representative of various examinations, have been investigated: adult lumbar spine; small field radiography and fluoroscopy; adult chest and paediatric pelvis and chest. For each scattering condition, the combinations of tube potential and grid ratio have been found which, for a well designed grid, result in the lowest mean absorbed dose in the phantom for a fixed contrast level. In examinations which generate large amounts of scatter, the use of high grid ratios in combination with high tube potentials is favourable with regard to both mean absorbed dose in the phantom and tube charge. When less scatter is generated, either the grid ratio or the tube potential can be varied to achieve the desired contrast level. High grid ratios require shorter exposure times, but need careful alignment in the beam to prevent primary radiation cut-off. It is shown that the air gap technique can be used to reduce patient dose in examinations with small amounts of scatter, but in combinations with a lower tube potential than when a grid is used.

  • 98.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Dance, David
    The Royal Marsden Hospital.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Monte Carlo study of grid performance in diagnostic radiology: task dependent opti­misation for screen-film imaging1994Ingår i: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 67, s. 76-85Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An optimization of anti-scatter grid design using Monte Carlo techniques in diagnostic radiology is presented. The criterion for optimization was to find the combinations of the grid parameters (lead strip width, grid ratio and strip density) and tube potential which result in the lowest mean absorbed dose in the patient at fixed image contrast. The optimization was performed in three irradiation geometries, representing different scattering conditions (paediatric examinations, and two adult lumbar spine examinations) and was restricted to grids using fibre materials in covers and interspaces. Grid designs currently available were studied, as were designs which use thinner strips (< 30 µm) and higher grid ratios (> 18). It was found that grids with widely different strip densities (strips cm–1) and grid ratios can have good performance provided that they are used with appropriate strip width and tube potential. With increasing amounts of scatter, the optimal grid requires thicker strips and higher grid ratios. Increasing the strip density and using thinner strips and higher grid ratios are generally required. Grids with low strip density (25 strips cm–1) were found to be less sensitive to alterations in strip width. Optimal grids for paediatric radiology require thinner strips (10–20 µm) than those in currently available grids. Grids on the market are best suited for examinations of the adult body in anteroposterior (AP) view. In the adult lateral view, representing the largest scattering volume, higher grid ratios (> 18) than those in existing grids would be optimal. Examples of good grid designs are given for each examination.

  • 99.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och vård, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Dance, David
    n/a.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Results from an optimisation of grid design in diagnostic radiology1995Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 57, nr 1, s. 211-215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results of an optimisation of grid design using a Monte Carlo model of the imaging chain are presented. Patient dose is significantly reduced by changing from aluminium to fibre grid covers and interspaces while keeping contrast constant. Numerous commercial grids have been investigated to identify superior designs. For optimal use, grids with high strip density require thinner lead strips and higher ratios than grids with low strip density. In paediatric radiology, grids with very thin strips (10-20 µm), or an air gap can be considered. In an adult lumbar spine examination, the optimal grid ratios are higher (greater than 15) than in commercial grids. This is particularly accentuated for grids with high strip density, fibre interspaces and in the lateral view. For a given imaging task, it is possible to identify grids of different design that have good performance, provided an appropriate strip width and tube potential are selected.

  • 100.
    Sandborg, Michael
    et al.
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Dance, David
    n/a.
    Alm Carlsson, Gudrun
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Östergötlands Läns Landsting, Kirurgi- och onkologicentrum, Radiofysikavdelningen. Linköpings universitet, Hälsouniversitetet.
    Persliden, Jan
    Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
    Selection of anti-scatter grids for different imaging tasks: the advantage of low atomic number cover and interspace materials1993Ingår i: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 66, s. 1151-1163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Monte Carlo computer program has been developed for the study of anti-scatter grids used in diagnostic radiology. The program estimates the scatter from soft tissue phantoms representative of either adult or paediatric examinations and uses dose increase, signal-to-noise ratio improvement and contrast improvement factors to study grid performance. It has been used to quantify the advantage of replacing grids with aluminium covers and interspaces by grids using materials of low atomic number for these components. Two approaches are used. First, the aluminium and low atomic number alternatives are compared for five grid ratios at fixed strip density and width and for tube potentials of 50, 70, 100 and 150 kV. Second, 44 commercially available grids are compared for three different imaging situations (lumbar spine, chest and paediatric). The results demonstrate that grids made with carbon fibre cover and cotton fibre interspace result in greater improvements in contrast and signal-to-noise ratio, and lower dose increase factors, than do grids made with aluminium. The dose reduction varies with irradiation conditions and is generally larger at lower tube potentials, higher grid ratios and lower strip densities. A typical reduction in mean absorbed dose in the patient is 30% in an adult lumbar spine (AP view) at 70 kV with a grid with 36 strips per centimetre and ratio 12.

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