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  • 1. Dance, D
    et al.
    Hunt, R
    Bakic, P
    Maidment, A
    Sandborg, Michael
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Ullman, Gustaf
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics.
    Alm-Carlsson, Gudrun
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Breast dosimetry using high-resolution voxel phantoms2005In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 359-363Article in journal (Refereed)
    Abstract [en]

    A computer model of X-ray mammography has been developed, which uses quasi-realistic high-resolution voxel phantoms to simulate the breast. The phantoms have 400 μm voxels and simulate the three-dimensional distributions of adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin and allow the estimation of dose to individual tissues. Calculations of the incident air kerma to mean glandular dose conversion factor, g, were made using a Mo/Mo spectrum at 28 kV for eight phantoms in the thickness range 40-80 mm and of varying glandularity. The values differed from standard tabulations used for breast dosimetry by up to 43%, because of the different spatial distribution of glandular tissue within the breast. To study this further, additional voxel phantoms were constructed, which gave variations of between 9 and 59% compared with standard values. For accurate breast dosimetry, it is therefore very important to take the distribution of glandular tissues into account. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 2. Hunt, R
    et al.
    Dance, D
    Bakic, P
    Maidment, A
    Sandborg, Michael
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Ullman, Gustaf
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics.
    Alm-Carlsson, Gudrun
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Calculation of the properties of digital mammograms using a computer simulation2005In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 395-398Article in journal (Refereed)
    Abstract [en]

    A Mote Carlo computer model of mammography has been developed to study and optimise the performance of digital mammographic systems. The program uses high-resolution voxel phantoms to model the breast, which simulate the adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin in three dimensions. The model calculates the dose to each tissue, and also the quantities such as energy imparted to image pixels, noise per image pixel and scatter-to-primary (S/P) ratios. It allows studies of the dependence of image properties on breast structure and on position within the image. The program has been calibrated by calculating and measuring the pixel values and noise for a digital mammographic system. The thicknesses of two components of this system were unknown, and were adjusted to obtain a good agreement between measurement and calculation. The utility of the program is demonstrated with the calculations of the variation of the S/P ratio with and without a grid, and of the image contrast across the image of a 50-mm-thick breast phantom. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 3. Hunt, R
    et al.
    Dance, D
    Pachoud, M
    Alm-Carlsson, Gudrun
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Sandborg, Michael
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Ullman, Gustaf
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics.
    Verdun, F
    Monte Carlo simulation of a mammographic test phantom2005In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 432-435Article in journal (Refereed)
    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.

  • 4. Håkansson, M
    et al.
    Båth, M
    Börjesson, S
    Kheddache, S
    Flinck, A
    Ullman, Gustaf
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics.
    Månsson, LG
    Nodule detection in digital chest radiography: Effect of nodule location2005In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 92-96Article in journal (Refereed)
    Abstract [en]

    Most detection studies in chest radiography treat the entire chest image as a single background or divided into the two regions parenchyma and mediastinum. However, the different parts of the lung show great variations in attenuation and structure, leading to different amounts of quantum noise and scattered radiation as well as different complexity. Detailed data on the difference in detectability in the different regions are of importance. The purpose of this study was to quantify the difference in detectability between different regions of a chest image. The chest X ray was divided into six different regions, where each region was considered to be uniform in terms of detectability. Thirty clinical chest images were collected and divided into the different regions. Simulated designer nodules with a full-width-at-fifth-maximum of 10 mm but with varying contrast were added to the images. An equal number of images lacking pathology were included and a receiver operating characteristic (ROC) study was conducted with five observers. Results show that the image contrast needed to obtain a constant value of Az (area under an ROC curve) differs by more than a factor of four between different regions. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 5.
    Sandborg, Michael
    et al.
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Tingberg, Anders
    Department of Radiation Physics, Malmö University Hospital, Malmö, Sweden.
    Ullman, Gustaf
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Joint Department of Physics, The Royal Marsden NHS Trust and Institute of Cancer Research, London.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages2006In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 33, no 11, p. 4169-4175Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to study the dependence of image quality in digital chest and pelvis radiography on tube voltage, and to explore correlations between clinical and physical measures of image quality. The effect on image quality of tube voltage in these two examinations was assessed using two methods. The first method relies on radiologists' observations of images of an anthropomorphic phantom, and the second method was based on computer modeling of the imaging system using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50–150  kV), including those values typically used with screen-film radiography. The tube charge was altered so that the same effective dose was achieved for each projection. Two x-ray units were employed using a computed radiography (CR) image detector with standard tube filtration and antiscatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from a Monte Carlo computer model in terms of the signal-to-noise ratio, SNR, of anatomical structures corresponding to the image criteria. Both the VGAS (visual grading analysis score) and SNR decrease with increasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages are employed. Hence, a positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analog screen-film radiography are discussed, as well as the relevance of using VGAS and quantum-noise SNR as measures of image quality in pelvis and chest radiography.

  • 6.
    Svalkvist, Angelica
    et al.
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Allansdotter Johnsson, Ase
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Vikgren, Jenny
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Hakansson, Markus
    University of Gothenburg, Sweden .
    Ullman, Gustaf
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Boijsen, Marianne
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Fisichella, Valeria
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Flinck, Agneta
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Molnar, David
    Sahlgrens University Hospital, Sweden .
    Mansson, Lars Gunnar
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Bath, Magnus
    University of Gothenburg, Sweden Sahlgrens University Hospital, Sweden .
    Evaluation of an improved method of simulating lung nodules in chest tomosynthesis2012In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 53, no 8, p. 874-884Article in journal (Refereed)
    Abstract [en]

    Background: Simulated pathology is a valuable complement to clinical images in studies aiming at evaluating an imaging technique. In order for a study using simulated pathology to be valid, it is important that the simulated pathology in a realistic way reflect the characteristics of real pathology. less thanbrgreater than less thanbrgreater thanPurpose: To perform a thorough evaluation of a nodule simulation method for chest tomosynthesis, comparing the detection rate and appearance of the artificial nodules with those of real nodules in an observer performance experiment. less thanbrgreater than less thanbrgreater thanMaterial and Methods: A cohort consisting of 64 patients, 38 patients with a total of 129 identified pulmonary nodules and 26 patients without identified pulmonary nodules, was used in the study. Simulated nodules, matching the real clinically found pulmonary nodules by size, attenuation, and location, were created and randomly inserted into the tomosynthesis section images of the patients. Three thoracic radiologists and one radiology resident reviewed the images in an observer performance study divided into two parts. The first part included nodule detection and the second part included rating of the visual appearance of the nodules. The results were evaluated using a modified receiver-operating characteristic (ROC) analysis. less thanbrgreater than less thanbrgreater thanResults: The sensitivities for real and simulated nodules were comparable, as the area under the modified ROC curve (AUC) was close to 0.5 for all observers (range, 0.43-0.55). Even though the ratings of visual appearance for real and simulated nodules overlapped considerably, the statistical analysis revealed that the observers to were able to separate simulated nodules from real nodules (AUC values range 0.70-0.74). less thanbrgreater than less thanbrgreater thanConclusion: The simulation method can be used to create artificial lung nodules that have similar detectability as real nodules in chest tomosynthesis, although experienced thoracic radiologists may be able to distinguish them from real nodules.

  • 7.
    Svalkvist, Angelica
    et al.
    University of Gothenburg.
    Hakansson, Markus
    University of Gothenburg.
    Ullman, Gustaf
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Bath, Magnus
    University of Gothenburg.
    Simulation of lung nodules in chest tomosynthesis2010In: RADIATION PROTECTION DOSIMETRY, ISSN 0144-8420, Vol. 139, no 1-3, p. 130-139Article in journal (Refereed)
    Abstract [en]

    The aim of the present work was to develop an adequate method for simulating lung nodules in clinical chest tomosynthesis images. Based on the visual appearance of real nodules, artificial, three-dimensional nodules with irregular shape and surface structure were created using an approach of combining spheres of different sizes and central points. The nodules were virtually positioned at the desired locations inside the patient and by using the known geometry of the tomosynthesis acquisition, the radiation emitted from the focal spot, passing through the nodule and reaching the detector could be simulated. The created nodules were thereby projected into raw-data tomosynthesis projection images before reconstruction of the tomosynthesis section images. The focal spot size, signal spread in the detector, scattered radiation, patient motion and existing anatomy at the location of the nodule were taken into account in the simulations. It was found that the blurring caused by the modulation transfer function and the patient motion overshadows the effects of a finite focal spot and aliasing and also obscures the surface structure of the nodules, which provides an opportunity to simplify the simulations and decrease the simulation times. Also, the limited in-depth resolution of the reconstructed tomosynthesis section images reduces the necessity to take details of the anatomical structures at the location of the inserted nodule into account.

  • 8.
    Svalkvist, Angelica
    et al.
    Dept. of Radiation Physics, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden.
    Ullman, Gustaf
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences. Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
    Håkansson, Markus
    Dept. of Radiation Physics, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden and Dept. of Diagnostic Radiology, Södra Älvsborgs Sjukhus, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Dance, David R.
    NCCPM, Royal Surrey County Hospital, Guildford , UK.
    Sandborg, Michael
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Department of Biomedical Engineering, Center for Medical Image Science and Visualization. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Radiation Physics.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Radiation Physics.
    Båth, Magnus
    Dept. of Radiation Physics, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden and fDept. of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis2011In: Medical Imaging 2011: Physics of Medical Imaging / [ed] Norbert J. Pelc; Ehsan Samei; Robert M. Nishikawa, SPIE - International Society for Optical Engineering, 2011, p. 79615Y-1-79615Y-10Conference paper (Other academic)
    Abstract [en]

    The primary aim of the present work was to analyze the effects of varying scatter-to-primary ratios on the appearance of simulated nodules in chest tomosynthesis section images. Monte Carlo simulations of the chest tomosynthesis system GE Definium 8000 VolumeRAD (GE Healthcare, Chalfont St. Giles, UK) were used to investigate the variation of scatter-to-primary ratios between different angular projections. The simulations were based on a voxel phantom created from CT images of an anthropomorphic chest phantom. An artificial nodule was inserted at 80 different positions in the simulated phantom images, using five different approaches for the scatter-to-primary ratios in the insertion process. One approach included individual determination of the scatter-to primary-ratio for each projection image and nodule location, while the other four approaches were using mean value, median value and zero degree projection value of the scatter-to-primary ratios at each nodule position as well as using a constant scatter-to-primary ratio of 0.5 for all nodule positions. The results indicate that the scatter-to-primary ratios vary up to a factor of 10 between the different angular tomosynthesis projections (±15°). However, the error in the resulting nodule contrast introduced by not taking all variations into account is in general smaller than 10 %.

  • 9.
    Ullman, Gustaf
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Accurate measures of both clinical image quality and patient radiation risk are needed for successful optimisation of medical imaging with ionising radiation. Optimisation in diagnostic radiology means finding the image acquisition technique that maximises the perceived information content and minimises the radiation risk or keeps it at a reasonably low level. The assessment of image quality depends on the diagnostic task and may in addition to system and quantum noise also be hampered by overlying projected anatomy.

    The main objective of this thesis is to develop methods for assessment of image quality in simulations of projection radiography. In this thesis, image quality is quantified by modelling the whole x‐ray imaging system including the x‐ray tube, patient, anti‐scatter device, image detector and the observer. This is accomplished by using Monte Carlo (MC) simulation methods that allow simultaneous estimates of measures of image quality and patient dose. Measures of image quality include the signal‐to‐noise‐ratio, SNR, of pathologic lesions and radiation risk is estimated by using organ doses to calculate the effective dose. Based on high‐resolution anthropomorphic phantoms, synthetic radiographs were calculated and used for assessing image quality with model‐observers (Laguerre‐Gauss (LG) Hotelling observer) that mimic real, human observers. Breast and particularly chest imaging were selected as study cases as these are particularly challenging for the radiologists.

    In chest imaging the optimal tube voltage in detecting lung lesions was investigated in terms of their SNR and the contrast of the lesions relative to the ribs. It was found that the choice of tube voltage depends on whether SNR of the lesion or the interfering projected anatomy (i.e. the ribs) is most important for detection. The Laguerre‐Gauss (LG) Hotelling observer is influenced by the projected anatomical background and includes this into its figure‐of‐merit, SNRhot,LG. The LG‐observer was found to be a better model of the radiologist than the ideal observer that only includes the quantum noise in its analysis. The measures of image quality derived from our model are found to correlate relatively well with the radiologist’s assessment of image quality. Therefore MC simulations can be a valuable and an efficient tool in the search for dose‐efficient imaging systems and image acquisition schemes.

    List of papers
    1. A search for optimal x‐ray spectra in iodine contrast media mammography
    Open this publication in new window or tab >>A search for optimal x‐ray spectra in iodine contrast media mammography
    Show others...
    2005 (English)In: Physics in medicine and biology, ISSN 0031-9155, Vol. 50, no 13, p. 3143-3152Article in journal (Refereed) Published
    Abstract [en]

    The aim of this work was to search for the optimal x-ray tube voltage and anode–filter combination in digital iodine contrast media mammography. In the optimization, two entities were of interest: the average glandular dose, AGD, and the signal-to-noise ratio, SNR, for detection of diluted iodine contrast medium. The optimum is defined as the technique maximizing the figure of merit, SNR2/AGD. A Monte Carlo computer program was used which simulates the transport of photons from the x-ray tube through the compression plate, breast, breast support plate, anti-scatter grid and image detector. It computes the AGD and the SNR of an iodine detail inside the compressed breast. The breast thickness was varied between 2 and 8 cm with 10–90% glandularity. The tube voltage was varied between 20 and 55 kV for each anode material (Rh, Mo and W) in combination with either 25 µm Rh or 0.05–0.5 mm Cu added filtration. The x-ray spectra were calculated with MCNP4C (Monte Carlo N-Particle Transport Code System, version 4C). A CsI scintillator was used as the image detector. The results for Rh/0.3mmCu, Mo/0.3mmCu and W/0.3mmCu were similar. For all breast thicknesses, a maximum in the figure of merit was found at approximately 45 kV for the Rh/Cu, Mo/Cu and W/Cu combinations. The corresponding results for the Rh/Rh combination gave a figure of merit that was typically lower and more slowly varying with tube voltage. For a 4 cm breast at 45 kV, the SNR2/AGD was 3.5 times higher for the Rh/0.3mmCu combination compared with the Rh/Rh combination. The difference is even larger for thicker breasts. The SNR2/AGD increases slowly with increasing Cu-filter thickness. We conclude that tube voltages between 41 and 55 kV and added Cu-filtration will result in significant dose advantage in digital iodine contrast media mammography compared to using the Rh/Rh anode/filter combination at 25–32 kV.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13217 (URN)10.1088/0031-9155/50/13/012 (DOI)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2015-03-20
    2. Distributions of scatter to primary ratios and signal to noise ratios per pixel in digital chest imaging
    Open this publication in new window or tab >>Distributions of scatter to primary ratios and signal to noise ratios per pixel in digital chest imaging
    Show others...
    2005 (English)In: Radiation protection dosimetry, ISSN 0144-8420, Vol. 114, no 1-3, p. 355-358Article in journal (Refereed) Published
    Abstract [en]

    The aim of this work was to calculate distributions of scatter-to-primary ratios (s/p) and signal-to-noise ratios per pixel (SNRp) in chest images. Such distributions may provide useful information on how physical image quality (contrast, SNR) is distributed over the posterior/anterior (PA) chest image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system (X-ray tube, anti-scatter grid and image detector). The calculations were performed for three PA thicknesses 20, 24 and 28 cm. For a 24 cm patient, the s/p varies between 0.5 in the lung to 2.5 behind the spine and heart. The corresponding variation of the SNRp is a factor of 3, with the highest values in the lung. Increasing the patient thickness from 20 to 28 cm increases the s/p by a factor of 2.2 behind the spine and heart.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13218 (URN)10.1093/rpd/nch530 (DOI)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2015-03-20
    3. Towards optimization in digital chest radiography using Monte Carlo modelling
    Open this publication in new window or tab >>Towards optimization in digital chest radiography using Monte Carlo modelling
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    2006 (English)In: Physics in medicine and biology, ISSN 0031-9155, Vol. 51, no 11, p. 2729-2743Article in journal (Refereed) Published
    Abstract [en]

    A Monte Carlo based computer model of the x-ray imaging system was used to investigate how various image quality parameters of interest in chest PA radiography and the effective dose E vary with tube voltage (90–150 kV), additional copper filtration (0–0.5 mm), anti-scatter method (grid ratios 8–16 and air gap lengths 20–40 cm) and patient thickness (20–28 cm) in a computed radiography (CR) system. Calculated quantities were normalized to a fixed value of air kerma (5.0 µGy) at the automatic exposure control chambers. Soft-tissue nodules were positioned at different locations in the anatomy and calcifications in the apical region. The signal-to-noise ratio, SNR, of the nodules and the nodule contrast relative to the contrast of bone (C/CB) as well as relative to the dynamic range in the image (Crel) were used as image quality measures. In all anatomical regions, except in the densest regions in the thickest patients, the air gap technique provides higher SNR and contrast ratios than the grid technique and at a lower effective dose E. Choice of tube voltage depends on whether quantum noise (SNR) or the contrast ratios are most relevant for the diagnostic task. SNR increases with decreasing tube voltage while C/CB increases with increasing tube voltage.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13219 (URN)10.1088/0031-9155/51/11/003 (DOI)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2015-03-20
    4. Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
    Open this publication in new window or tab >>Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
    Show others...
    2006 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 33, no 11, p. 4169-4175Article in journal (Refereed) Published
    Abstract [en]

    The aim of this work was to study the dependence of image quality in digital chest and pelvis radiography on tube voltage, and to explore correlations between clinical and physical measures of image quality. The effect on image quality of tube voltage in these two examinations was assessed using two methods. The first method relies on radiologists' observations of images of an anthropomorphic phantom, and the second method was based on computer modeling of the imaging system using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50–150  kV), including those values typically used with screen-film radiography. The tube charge was altered so that the same effective dose was achieved for each projection. Two x-ray units were employed using a computed radiography (CR) image detector with standard tube filtration and antiscatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from a Monte Carlo computer model in terms of the signal-to-noise ratio, SNR, of anatomical structures corresponding to the image criteria. Both the VGAS (visual grading analysis score) and SNR decrease with increasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages are employed. Hence, a positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analog screen-film radiography are discussed, as well as the relevance of using VGAS and quantum-noise SNR as measures of image quality in pelvis and chest radiography.

    Keyword
    diagnostic radiography, Monte Carlo methods, image denoising, dosimetry, phantoms, biomedical equipment
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13220 (URN)10.1118/1.2362871 (DOI)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2017-12-13
    5. Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods
    Open this publication in new window or tab >>Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods
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    2006 (English)In: Proceedings of SPIE, 2006, Vol. 6142Conference paper, Published paper (Refereed)
    Abstract [en]

    Monte Carlo (MC) computer simulation of chest x-ray imaging systems has hitherto been performed using anthropomorphic phantoms with too large (3 mm) voxel sizes. The aim for this work was to develop and use a Monte Carlo computer program to compute projection x-ray images of a high-resolution anthropomorphic voxel phantom for visual clinical image quality evaluation and dose-optimization. An Alderson anthropomorphic chest phantom was imaged in a CT-scanner and reconstructed with isotropic voxels of 0.7 mm. The phantom was segmented and included in a Monte Carlo computer program using the collision density estimator to derive the energies imparted to the detector per unit area of each pixel by scattered photons. The image due to primary photons was calculated analytically including a pre-calculated detector response function. Attenuation and scatter of x-rays in the phantom, grid and image detector was considered. Imaging conditions (tube voltage, anti-scatter device) were varied and the images compared to a real computed radiography (Fuji FCR 9501) image. Four imaging systems were simulated (two tube voltages 81 kV and 141 kV using either a grid with ratio 10 or a 30 cm air gap). The effect of scattered radiation on the visibility of thoracic vertebrae against the heart and lungs is demonstrated. The simplicity in changing the imaging conditions will allow us not only to produce images of existing imaging systems, but also of hypothetical, future imaging systems. We conclude that the calculated images of the high-resolution voxel phantom are suitable for human detection experiments of low-contrast lesions.

    Series
    ; 6142
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13221 (URN)10.1117/12.644119 (DOI)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2015-03-20
    6. Development of a Monte Carlo based model for optimization using the Laguerre‐Gauss Hotelling observer
    Open this publication in new window or tab >>Development of a Monte Carlo based model for optimization using the Laguerre‐Gauss Hotelling observer
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    2008 (English)In: Medical physics, ISSN 0094-2405Article in journal (Refereed) Submitted
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-13222 (URN)
    Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2017-01-11
  • 10.
    Ullman, Gustaf
    et al.
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Båth, Magnus
    Alm Carlsson, Gudrun
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Tapiovaara, Markku
    Sandborg, Michael
    Linköping University, Department of Medical and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Development of a Monte Carlo based model for optimization using the Laguerre‐Gauss Hotelling observer2008In: Medical physics, ISSN 0094-2405Article in journal (Refereed)
  • 11.
    Ullman, Gustaf
    et al.
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Royal Surrey County Hospital, Guildford.
    Sandborg, Michael
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Alm Carlsson, Gudrun
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medicine and Health Sciences, Radiation Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Svalkvist, Angelica
    University of Gothenburg.
    Båth, Magnus
    University of Gothenburg.
    A Monte Carlo-based model for simulation of digital chest tomosynthesis2010In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 139, no 1-3, p. 159-163Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to calculate synthetic digital chest tomosynthesis projections using a computer simulation model based on the Monte Carlo method. An anthropomorphic chest phantom was scanned in a computed tomography scanner, segmented and included in the computer model to allow for simulation of realistic high-resolution X-ray images. The input parameters to the model were adapted to correspond to the VolumeRAD chest tomosynthesis system from GE Healthcare. Sixty tomosynthesis projections were calculated with projection angles ranging from +15 to −15°. The images from primary photons were calculated using an analytical model of the anti-scatter grid and a pre-calculated detector response function. The contributions from scattered photons were calculated using an in-house Monte Carlo-based model employing a number of variance reduction techniques such as the collision density estimator. Tomographic section images were reconstructed by transferring the simulated projections into the VolumeRAD system. The reconstruction was performed for three types of images using: (i) noise-free primary projections, (ii) primary projections including contributions from scattered photons and (iii) projections as in (ii) with added correlated noise. The simulated section images were compared with corresponding section images from projections taken with the real, anthropomorphic phantom from which the digital voxel phantom was originally created. The present article describes a work in progress aiming towards developing a model intended for optimisation of chest tomosynthesis, allowing for simulation of both existing and future chest tomosynthesis systems.

  • 12.
    Ullman, Gustaf
    et al.
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Malusek, Alexandr
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Dance, David R.
    The Royal Marsden NHS Trust, United Kingdom.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods2006In: Proceedings of SPIE, 2006, Vol. 6142Conference paper (Refereed)
    Abstract [en]

    Monte Carlo (MC) computer simulation of chest x-ray imaging systems has hitherto been performed using anthropomorphic phantoms with too large (3 mm) voxel sizes. The aim for this work was to develop and use a Monte Carlo computer program to compute projection x-ray images of a high-resolution anthropomorphic voxel phantom for visual clinical image quality evaluation and dose-optimization. An Alderson anthropomorphic chest phantom was imaged in a CT-scanner and reconstructed with isotropic voxels of 0.7 mm. The phantom was segmented and included in a Monte Carlo computer program using the collision density estimator to derive the energies imparted to the detector per unit area of each pixel by scattered photons. The image due to primary photons was calculated analytically including a pre-calculated detector response function. Attenuation and scatter of x-rays in the phantom, grid and image detector was considered. Imaging conditions (tube voltage, anti-scatter device) were varied and the images compared to a real computed radiography (Fuji FCR 9501) image. Four imaging systems were simulated (two tube voltages 81 kV and 141 kV using either a grid with ratio 10 or a 30 cm air gap). The effect of scattered radiation on the visibility of thoracic vertebrae against the heart and lungs is demonstrated. The simplicity in changing the imaging conditions will allow us not only to produce images of existing imaging systems, but also of hypothetical, future imaging systems. We conclude that the calculated images of the high-resolution voxel phantom are suitable for human detection experiments of low-contrast lesions.

  • 13.
    Ullman, Gustaf
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics.
    Sandborg, Michael
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Dance, D
    Hunt, R
    Alm-Carlsson, Gudrun
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiation Physics. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    The influence of patient thickness and imaging system on patient dose and physical image quality in digital chest imaging2005In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 294-297Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to study the influence of patient thickness, tube voltage and image detector on patient dose, contrast and ideal observer signal-to-noise ratio (SNRI), for pathological details positioned at different regions in the image in posterior-anterior (PA) chest radiology. A Monte Carlo computational model was used to compute measures of physical image quality (contrast, SNRI) and patient effective dose, E. Two metastasis-like details positioned in the central right lung and right lung near the spine, respectively, were studied. The tube voltage was varied between 100 and 150 kV and the patient thickness between 20 and 28 cm. Both, a computed radiography (CR) system and a direct radiography (DR) system, were investigated. The DR system provides both lower doses and better image quality compared with the CR system. The SNRI2/E is ∼2.9 times higher for the DR system compared with the CR system. © The Author 2005. Published by Oxford University Press. All rights reserved.

  • 14.
    Ullman, Gustaf
    et al.
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Joint Department of Physics, The Royal Marsden NHS Foundation Trust and Institute of Cancer Research, London, UK.
    Hunt, Roger A.
    Joint Department of Physics, The Royal Marsden NHS Foundation Trust and Institute of Cancer Research, London, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Towards optimization in digital chest radiography using Monte Carlo modelling2006In: Physics in medicine and biology, ISSN 0031-9155, Vol. 51, no 11, p. 2729-2743Article in journal (Refereed)
    Abstract [en]

    A Monte Carlo based computer model of the x-ray imaging system was used to investigate how various image quality parameters of interest in chest PA radiography and the effective dose E vary with tube voltage (90–150 kV), additional copper filtration (0–0.5 mm), anti-scatter method (grid ratios 8–16 and air gap lengths 20–40 cm) and patient thickness (20–28 cm) in a computed radiography (CR) system. Calculated quantities were normalized to a fixed value of air kerma (5.0 µGy) at the automatic exposure control chambers. Soft-tissue nodules were positioned at different locations in the anatomy and calcifications in the apical region. The signal-to-noise ratio, SNR, of the nodules and the nodule contrast relative to the contrast of bone (C/CB) as well as relative to the dynamic range in the image (Crel) were used as image quality measures. In all anatomical regions, except in the densest regions in the thickest patients, the air gap technique provides higher SNR and contrast ratios than the grid technique and at a lower effective dose E. Choice of tube voltage depends on whether quantum noise (SNR) or the contrast ratios are most relevant for the diagnostic task. SNR increases with decreasing tube voltage while C/CB increases with increasing tube voltage.

  • 15.
    Ullman, Gustaf
    et al.
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Joint Department of Physics, The Royal Marsden NHS Trust, London, UK .
    Hunt, Roger
    Joint Department of Physics, The Royal Marsden NHS Trust, London, UK .
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Distributions of scatter to primary ratios and signal to noise ratios per pixel in digital chest imaging2005In: Radiation protection dosimetry, ISSN 0144-8420, Vol. 114, no 1-3, p. 355-358Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to calculate distributions of scatter-to-primary ratios (s/p) and signal-to-noise ratios per pixel (SNRp) in chest images. Such distributions may provide useful information on how physical image quality (contrast, SNR) is distributed over the posterior/anterior (PA) chest image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system (X-ray tube, anti-scatter grid and image detector). The calculations were performed for three PA thicknesses 20, 24 and 28 cm. For a 24 cm patient, the s/p varies between 0.5 in the lung to 2.5 behind the spine and heart. The corresponding variation of the SNRp is a factor of 3, with the highest values in the lung. Increasing the patient thickness from 20 to 28 cm increases the s/p by a factor of 2.2 behind the spine and heart.

  • 16.
    Ullman, Gustaf
    et al.
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Dance, David R.
    Joint Department of Physics, The Royal Marsden NHS Trust, London, UK.
    Yaffe, Martin
    Department of Medical Biophysics, University of Toronto, Sunnybrook and Women's College Health Sciences Centre, Ontario, Canada.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    A search for optimal x‐ray spectra in iodine contrast media mammography2005In: Physics in medicine and biology, ISSN 0031-9155, Vol. 50, no 13, p. 3143-3152Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to search for the optimal x-ray tube voltage and anode–filter combination in digital iodine contrast media mammography. In the optimization, two entities were of interest: the average glandular dose, AGD, and the signal-to-noise ratio, SNR, for detection of diluted iodine contrast medium. The optimum is defined as the technique maximizing the figure of merit, SNR2/AGD. A Monte Carlo computer program was used which simulates the transport of photons from the x-ray tube through the compression plate, breast, breast support plate, anti-scatter grid and image detector. It computes the AGD and the SNR of an iodine detail inside the compressed breast. The breast thickness was varied between 2 and 8 cm with 10–90% glandularity. The tube voltage was varied between 20 and 55 kV for each anode material (Rh, Mo and W) in combination with either 25 µm Rh or 0.05–0.5 mm Cu added filtration. The x-ray spectra were calculated with MCNP4C (Monte Carlo N-Particle Transport Code System, version 4C). A CsI scintillator was used as the image detector. The results for Rh/0.3mmCu, Mo/0.3mmCu and W/0.3mmCu were similar. For all breast thicknesses, a maximum in the figure of merit was found at approximately 45 kV for the Rh/Cu, Mo/Cu and W/Cu combinations. The corresponding results for the Rh/Rh combination gave a figure of merit that was typically lower and more slowly varying with tube voltage. For a 4 cm breast at 45 kV, the SNR2/AGD was 3.5 times higher for the Rh/0.3mmCu combination compared with the Rh/Rh combination. The difference is even larger for thicker breasts. The SNR2/AGD increases slowly with increasing Cu-filter thickness. We conclude that tube voltages between 41 and 55 kV and added Cu-filtration will result in significant dose advantage in digital iodine contrast media mammography compared to using the Rh/Rh anode/filter combination at 25–32 kV.

  • 17.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Validation of Voxman Monte Carlo code and calibration for digital systems2003Report (Other academic)
    Abstract [en]

    The objective of this work was to test the Monte Carlo model ‘Voxman’ against measurements on x-ray systems in the clinic. X-ray transmission experiments are performed to test of the accuracy of the Monte Carlo photon transport. Experiments were also performed with an image plate (CR) system in the clinic to compare the measured pixel values with calculated pixel values. Measurements were also performed with the automatic exposure control (AEC) chambers used in Linköping and Motala. The purpose for those measurements was to choose a normalisation of the entrance surface dose.

  • 18.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Dance, David R
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Båth, M.
    Department of Radiation Physics, Göteborg, Sweden.
    Håkansson, M.
    Department of Radiation Physics, Göteborg, Sweden.
    Börjesson, S.
    Department of Radiation Physics, Göteborg, Sweden.
    Hunt, Roger
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    On the extent of quantum noise limitation in digital chest radiography2004Report (Other academic)
    Abstract [en]

    The aim for this work was to study to what extent the detection of nodules is quantum noise limited, based on the combined results from a nodule-detection clinical trial and a Monte Carlo computational model of a digital chest imaging system. The Monte Carlo computer program computes measures of physical image quality such as image contrast, C and signalto-noise ratio, SNR for nodules of any size. A computed radiography (CR) imaging system used simulated. The patient anterior-posterior thickness was 25 cm and nodules with diameters between 1-40 mm were included. The image contrast and SNR was calculated for 1600 (40x40) positions in the chest image and averaged over five anatomical regions of interest (lateral pulmonary, retrocardial, hilar, lower- and upper mediastinal regions). Threshold contrasts for each region, Cth, corresponding to Az=0.80 for detecting a 10 mm nodule, were deduced from the clinical trial. A threshold is also used for the quantum noise signal-to-noise ratio, SNRth. The model computes the diameter of a disk-shaped object that is required to comply with the two criteria: SNR≥SNRth and C≥Cth. A system is said to be quantum noise limited when the nodule size required to fulfil both criteria is not limited by the contrast but by the SNR. The required nodule diameter is largest in the hilar region (25 mm) and smallest in the lateral pulmonary region (11 mm). When the threshold SNRth=25 is used, the lower mediastinal region is quantum noise limited already at low speed classes (S>100). The hilar region is never quantum noise limited at realistic speed classes (S<1000). The accuracy of this model will be tested in the future by more sophisticated modelling of anatomical background and noise in the SNR-expression.

  • 19.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Dance, David R
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Hunt, Roger
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Distributions of scatter-to-primary ratios in chest PA radiography using grid or air gap for scatter-rejection2004Report (Other academic)
    Abstract [en]

    The aim for this work was to calculate distributions of scatter-to-primary ratios (εs/εp) and signal-to-noise ratios per pixel (SNRp) for a large set of imaging systems with either grid or air gap for scatter rejection. Grids with ratio 8-16 and air gap length 20 and 40 cm were used. The tube voltage was varied between 90-150 kV and three patient thickness between 20-28 cm were tested in order to compare scatter-rejections techniques for different conditions. Distributions of this sort may provide useful information on how physical image quality (contrast, SNR) is distributed over the chest PA image. A Monte Carlo computer program was used for the calculations, including a model of both the patient (voxel phantom) and the imaging system. The mean value of the εs/εp is 0.39 in the hilar region and 1.72 in the lower mediastinal region. For a 28 cm patient, the corresponding values are 0.42 in the hilar region and 2.58 in the lower mediastinal region. The grid with ratio 16 is the most efficient scatter rejection technique in all regions except the hilar region. In the hilar region, the most efficient technique is the 40 cm air gap.

  • 20.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Dance, David R
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Hunt, Roger
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Optimisation of chest radiology by computer modelling of image quality measures and patient effective dose2004Report (Other academic)
    Abstract [en]

    A set of modelled computed radiography (CR) systems are compared with a reference system. Calculations are performed, which compares the effective dose and a set of figures of merit corresponding to the image quality of both the modelled systems and the reference system. For a nodule with soft tissue corresponding, the signal-to-noise ratio, SNR, is found to decrease with increasing tube voltage. On the other hand, the ratio of the contrast of the nodule compared to the contrast of a rib (nodule-to-rib contrast-ratio) is found to increase with increasing tube voltage.

  • 21.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Hunt, Roger
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Dance, David R
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Implementation of pathologies in the Monte Carlo model in chest and breast imaging2003Report (Other academic)
    Abstract [en]

    The Monte Carlo simulation model of the chest and breast imaging systems including a voxelised model of the patient are used to compute measures of image quality and patient absorbed dose. It is important that the model computes measures of image quality of pathological details that are similar in size, composition and position as real pathological details in typical chest and breast images. Moreover, the other partners of the co-coordinated research project will produce hybrid images with pathological details and have these images assessed by a group of radiologist. The model will then be used to study to what extent variations in clinical image quality can be explained by variations in physical image quality, for example signal-to-noise ratio. This report summarizes the selection of pathological details to include in the model of chest and breast imaging systems.

  • 22.
    Ullman, Gustav
    et al.
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Tingberg, Anders
    Department of Radiation Physics, Malmö University Hospital, Sweden.
    Dance, David R
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Hunt, Roger
    Department of Physics, The Royal Marsden NHS Trust, UK.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Care, Radio Physics. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics.
    Comparison of clinical and physical measures of image quality in chest PA and pelvis AP views at varying tube voltages2004Report (Other academic)
    Abstract [en]

    Image quality in digital chest PA and pelvis AP was assessed using two different methods; one based on observations of images of an anthropomorphic phantom, one based on computer modelling using an anthropomorphic voxel phantom. The tube voltage was varied within a broad range (50-150 kV), including those values typically used with screen-film radiography. The tube charge was altered so that approximately the same effective dose was achieved in the modelled patient (anthropomorphic phantom). Two x-ray units were employed using a digital image detector (computed radiography, CR, system) with standard tube filtration and anti-scatter device. Clinical image quality was assessed by a group of radiologists using a visual grading analysis (VGA) technique based on the revised CEC image criteria. Physical image quality was derived from the computer model in terms of the signal-to-noise ratio, SNR for fixed effective dose in the voxel phantom. The computer model uses Monte Carlo simulations of the patient and complete imaging system. Both the VGAS (visual grading analysis score) and SNR increase with decreasing tube voltage in both chest PA and pelvis AP examinations, indicating superior performance if lower tube voltages than used today are employed in digital radiology. A positive correlation between clinical and physical measures of image quality was found. The pros and cons of using lower tube voltages with CR digital radiography than typically used in analogue screen-film radiography are discussed as well as the relevance of using VGAS and quantum noise SNR as measures of image quality.

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