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Ullman, Gustaf
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Publications (10 of 22) Show all publications
Svalkvist, A., Allansdotter Johnsson, A., Vikgren, J., Hakansson, M., Ullman, G., Boijsen, M., . . . Bath, M. (2012). Evaluation of an improved method of simulating lung nodules in chest tomosynthesis. Acta Radiologica, 53(8), 874-884
Open this publication in new window or tab >>Evaluation of an improved method of simulating lung nodules in chest tomosynthesis
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2012 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 53, no 8, p. 874-884Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Informa Healthcare / Wiley-Blackwell / Royal Society of Medicine Press, 2012
Keywords
Thorax, digital radiography, lung, adults, observer performance, technology assessments
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-86133 (URN)10.1258/ar.2012.120230 (DOI)000310820000009 ()
Note

Funding Agencies|Swedish Research Council|2011-488|Swedish Radiation Safety Authority|2008/22322009/16892010/43632012/2021|King Gustav V Jubilee Clinic Cancer Research Foundation|2007:282008:50|Swedish Federal Government under the LUA/ALF agreement|ALFGBG-136281|Health & Medical Care Committee of the Region Vastra Gotaland|VGFOUREG-12046VGFOUREG-27551VGFOUREG-81341|

Available from: 2012-12-07 Created: 2012-12-07 Last updated: 2017-12-07
Svalkvist, A., Ullman, G., Håkansson, M., Dance, D. R., Sandborg, M., Alm Carlsson, G. & Båth, M. (2011). Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis. In: Norbert J. Pelc; Ehsan Samei; Robert M. Nishikawa (Ed.), Medical Imaging 2011: Physics of Medical Imaging. Paper presented at Medical Imaging 2011: Physics of Medical Imaging, 12 February 20011, Lake Buena Vista, Florida, USA (pp. 79615Y-1-79615Y-10). SPIE - International Society for Optical Engineering
Open this publication in new window or tab >>Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis
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2011 (English)In: 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, Published 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 %.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2011
Series
Proceedings of SPIE (Progress in biomedical optics and imaging), ISSN 1605-7422 ; 7961
Keywords
TSYN, XIM
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-68292 (URN)10.1117/12.873173 (DOI)000294178500201 ()9780819485038 (ISBN)
Conference
Medical Imaging 2011: Physics of Medical Imaging, 12 February 20011, Lake Buena Vista, Florida, USA
Note

Original Publication: Angelica Svalkvist, Gustaf Ullman, Markus Håkansson, David Dance, Michael Sandborg, Gudrun Alm Carlsson and Magnus Båth, Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis, 2011, Proc SPIE 7961, 79615Y. http://dx.doi.org/10.1117/12.873173 Copyright 2011 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

Available from: 2011-05-18 Created: 2011-05-18 Last updated: 2015-03-20Bibliographically approved
Ullman, G., Dance, D. R., Sandborg, M., Alm Carlsson, G., Svalkvist, A. & Båth, M. (2010). A Monte Carlo-based model for simulation of digital chest tomosynthesis. Radiation Protection Dosimetry, 139(1-3), 159-163
Open this publication in new window or tab >>A Monte Carlo-based model for simulation of digital chest tomosynthesis
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2010 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 139, no 1-3, p. 159-163Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Oxford: Oxford University Press, 2010
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-56402 (URN)10.1093/rpd/ncq079 (DOI)000277738200027 ()20203125 (PubMedID)
Note
This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Radiation Protection Dosimetry following peer review. The definitive publisher-authenticated version: Gustaf Ullman, David R. Dance, Michael Sandborg, Gudrun Alm Carlsson, Angelica Svalkvist and Magnus Båth, A MONTE CARLO-BASED MODEL FOR SIMULATION OF DIGITAL CHEST TOMOSYNTHESIS, 2010, Radiation Protection Dosimetry, (139), 1-3, 159-163. is available online at: http://dx.doi.org/10.1093/rpd/ncq079 Copyright: Oxford University Press http://www.oxfordjournals.org/ Available from: 2010-05-10 Created: 2010-05-10 Last updated: 2017-12-12
Svalkvist, A., Hakansson, M., Ullman, G. & Bath, M. (2010). Simulation of lung nodules in chest tomosynthesis. RADIATION PROTECTION DOSIMETRY, 139(1-3), 130-139
Open this publication in new window or tab >>Simulation of lung nodules in chest tomosynthesis
2010 (English)In: RADIATION PROTECTION DOSIMETRY, ISSN 0144-8420, Vol. 139, no 1-3, p. 130-139Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Oxford University Press, 2010
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-56793 (URN)10.1093/rpd/ncp308 (DOI)000277738200023 ()
Available from: 2010-06-04 Created: 2010-06-04 Last updated: 2010-06-04
Ullman, G., Båth, M., Alm Carlsson, G., Dance, D. R., Tapiovaara, M. & Sandborg, M. (2008). Development of a Monte Carlo based model for optimization using the Laguerre‐Gauss Hotelling observer. Medical physics
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
Ullman, G. (2008). Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers. (Doctoral dissertation). Institutionen för medicin och hälsa
Open this publication in new window or tab >>Quantifying image quality in diagnostic radiology using simulation of the imaging system and model observers
2008 (English)Doctoral 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.

Place, publisher, year, edition, pages
Institutionen för medicin och hälsa, 2008
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1050
Keywords
radiology, radiation physics, image quality, optimisation, effective dose, chest radiography
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:liu:diva-11662 (URN)9789173939522 (ISBN)
Public defence
2008-05-09, Eken, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2008-04-28 Created: 2008-04-28 Last updated: 2017-12-15
Ullman, G., Malusek, A., Sandborg, M., Dance, D. R. & Alm Carlsson, G. (2006). Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods. In: Proceedings of SPIE: . , 6142
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
Sandborg, M., Tingberg, A., Ullman, G., Dance, D. R. & Alm Carlsson, G. (2006). Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages. Medical physics (Lancaster), 33(11), 4169-4175
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
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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.

Keywords
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
Ullman, G., Sandborg, M., Dance, D. R., Hunt, R. A. & Alm Carlsson, G. (2006). Towards optimization in digital chest radiography using Monte Carlo modelling. Physics in medicine and biology, 51(11), 2729-2743
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
Ullman, G., Sandborg, M., Dance, D. R., Yaffe, M. & Alm Carlsson, G. (2005). A search for optimal x‐ray spectra in iodine contrast media mammography. Physics in medicine and biology, 50(13), 3143-3152
Open this publication in new window or tab >>A search for optimal x‐ray spectra in iodine contrast media mammography
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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
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