| 1. |
- Niemi, MEK, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 3. |
- Fredenberg, Erik, et al.
(författare)
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Measurement of breast-tissue x-ray attenuation by spectral mammography : solid lesions
- 2016
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Ingår i: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 61:7, s. 2595-2612
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature.
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| 4. |
- Fredenberg, Erik, et al.
(författare)
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X-ray attenuation of adipose breast tissue : In-vitro and in-vivo measurements using spectral imaging
- 2015
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Ingår i: MEDICAL IMAGING 2015: PHYSICS OF MEDICAL IMAGING. - : SPIE. - 9781628415025
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Konferensbidrag (refereegranskat)abstract
- The development of new x-ray imaging techniques often requires prior knowledge of tissue attenuation, but the sources of such information are sparse. We have measured the attenuation of adipose breast tissue using spectral imaging, in vitro and in vivo. For the in-vitro measurement, fixed samples of adipose breast tissue were imaged on a spectral mammography system, and the energy-dependent x-ray attenuation was measured in terms of equivalent thicknesses of aluminum and poly-methyl methacrylate (PMMA). For the in-vivo measurement, a similar procedure was applied on a number of spectral screening mammograms. The results of the two measurements agreed well and were consistent with published attenuation data and with measurements on tissue-equivalent material.
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| 5. |
- Sandborg, Michael, et al.
(författare)
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Calculation of contrast and signal-to-noise degradation factors for digital detectors in chest and breast imaging
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Monte Carlo model of an x-ray imaging system, used in the EU 5th framework project by the Linköping and London partner to study chest and breast imaging, was developed jointly by the London and Linköping partners. It incorporates a model of the x-ray imaging system (x-ray tube, filtration, anti-scatter device and image receptor etc.) and the patient by using a voxel phantom of an adult male. Validation and calibration experiments have been performed for both the chest (Ullman et al 2003b) and the breast model. The model allows inclusion of anatomical or pathological details at particular positions in the anatomy and is able to calculate measures of image quality such as contrast and signal-to-noise ratio and measures of radiation risk for example entrance air kerma and effective dose. It allows alteration of imaging system settings such as tube voltage, filtration, beam size and position, choice of anti-scatter device and choice of image detector etc. The model is a useful tool for optimisations since it has been shown that in chest and lumbar spine radiography is able to predict clinical image quality as assessed by a group of radiologists. In the Monte Carlo model (MC-model) the image quality measures are calculated assuming a perfectly sharp imaging system and correction factors need to be applied to the computed data in order to make the image quality measures agree on an absolute scale. The calculation of correction factors for contrast and signal-tonoises are described in this report. A similar report focusing on analogue screen-film chest and lumbar spine radiography was completed some years ago and some of the concepts and methods are similar.
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| 6. |
- Sandborg, Michael, et al.
(författare)
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Collection and analysis of patient and image data for calibration of a voxelphantombased Monte Carlo code and for the modelling of important structures
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The contribution of the Medical Physics Departments at Linköping University (LKP) and The Royal Marsden NHS Trust (RMH) to the joint project ‘Predictivity and Optimisation in Medical Radiation Protection’ is in modelling of the chest and lumbar spine radiographic examinations. This involves:the development of quantitative imaging requirements;an investigation of the effect of imaging technique on image quality and patientdose, andan optimisation of system design.One of the objectives for this first reporting period (0-12 months) was to collect a set of chest and lumbar spine radiographs of patients for subsequent analysis in order to establish patient doses and important features in the images. The set of radiographs and the outcome of the image feature analysis will during this project’s second year be used to calibrate our Monte Carlo computational model of the conventional chest and lumbar spine screen-film X-ray imaging systems.
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| 7. |
- Sandborg, Michael, et al.
(författare)
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Comparison of clinical and physical measures of image quality in chest and pelvis computed radiography at different tube voltages
- 2006
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 33:11, s. 4169-4175
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Sandborg, Michael, et al.
(författare)
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Implementation of unsharpness and noise into the model of the imaging system : Applications to chest and lumbar spine screen-film radiography
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A model of the complete x-ray imaging system including the patient is a powerful tool for imaging system analysis and the optimisation of image quality and patient dose. It allows flexible variation of the system components (i.e. x-ray source, antiscatter device and image detector) and study of their effect on image quality and patient risk. Our group has developed, validated and calibrated a Monte Carlo model of the complete imaging system for chest and lumbar spine examination including voxalised human male anatomy. The Monte Carlo program calculates the contrast and signal-to-noise ratio (SNR) of various contrasting details within the voxel phantom. Important details in the images have been selected by consulting radiologist and the EU document of image quality criteria. The entrance surface dose without back-scatter and the effective dose are used as measures of patient radiation risk. The contrasts of the details are derived initially from Monte Carlo estimates of the energy imparted per unit area to the image detector beside and behind the detail. However, this ignores the effects of unsharpness in the imaging chain (such as screen-film, geometric and motion unsharpness) and the influence on contrast of the film characteristic curve. In the Monte Carlo program, SNR is calculated assuming that the noise arises from the random fluctuations in the energy imparted per unit area to the image detector only. However, other noise sources also contribute to the total noise, such as screen and film noise. Hence the model of the imaging system needs to be further developed to take these effects into account. The methods used to extend the model are described below together with illustrations of their effect on the difference in optical density, DOD, and SNR in chest and lumbar spine imaging.
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| 9. |
- Sandborg, Michael, et al.
(författare)
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Report on the study and optimisation of chestand lumbar spine X-ray imaging
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The optimisation of radiological equipment and equipment parameters is a key stage in the optimisation of image quality and patient dose in diagnostic radiology. It is essential, however, to underpin such optimisation with theoretical modelling which can provide both the direct quantification of the effect on image quality and dose of changes in system parameters and the opportunity for optimisation of equipment selection and use. Our principal contribution to the joint CEC-project 'Predictivity and Optimisation in Diagnostic Radiology' is in modelling of planar chest and lumbar spine radiographic examinations. The results of this work for the chest PA, lumbar spine AP and lumbar spine lateral examinations are presented in this report. Prior to this, several development stages have been completed which include the calibration and validation of our methods by measurements in the clinical environment on patients and patient images. These important aspects are not dealt with in detail here, but are described in separate reports. This report focuses on three aspects from our results of using our Monte Carlo model of the patient and imaging equipment: (1) Study of the effects on image quality and patient dose when the imaging parameters are varied; Establishment of imaging parameters and systems that result in as least as good image quality as systems with good performance singled out from results of clinical trials (optimisations); Comparison of the results from the model with the results from clinical trials performed by partners in the joint CEC-project. An objective of the report is to present our results at a level of detail not usually possible in the refereed scientific literature. The report should therefore not be read all at once, but preferably used as a ‘reference library’ or documentation of all our efforts. There are many interesting results and findings from this collaborative work and these will be submitted for publication to the appropriate journals.
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| 10. |
- Sandborg, Michael, et al.
(författare)
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The choice of anti-scatter grids in diagnostic radiology : the optimization of image quality and absorbed dose
- 1993
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A Monte Carlo model is developed to study and optimise the design of antiscatter grids in diagnostic radiology. The imaging chain including X-ray energy spectra, phantom (representing the patient), grid and image receptor is simulated. Image quality is quantified in terms of contrast (conventionai screen-film imaging) and signal-to-noise ratio, SNR (digital imaging) and the radiation detriment to the patient (risk) by the mean absorbed dose in the phantom. The advantages of using fibre instead of aluminium for grid interspaces and covers are quantified. Compared to aluminium grids, the absorbed dose is reduced by 10-50%, contrast is improved by 0-10% and SNR by 10-40% (digital radiography). The advantages are larger at low tube potentials and for grids with high ratio and low strip density. Commercial grids, with different interspace materials, strip density, strip width and grid ratio, are compared in paediatric, lumbar spine and chest examinations. The differences in dose increase and contrast improvement factors obtained with these grids are mainly due to the use of different materials in the grid interspaces, but the strip design is also important. In a global optimisation of grid design and tube potential at fixed contrast, it is found that grids of different strip density and ratio all can have good performances provided that they are used with appropriate strip width and tube potential. In the paediatric examination, low ratio grids need thinner strips than used today to be optimal. A small air gap could alternatively be used. In examinations with more scatter (adult AP), present commercial grids are optimal (r=12-16, d=30-50µm). In the lateral view (even more scatter), grids with ratios larger than 16 are optimal provided the grid can be accurately aligned in the beam. The optimization is performed with grids with fibre interspaces and covers since low atomic number materials should preferably be used for materials between the patient and the receptor. Optimal grids with aluminium for these components have lower grid ratio and higher strip densities than optimal fibre grids.
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| 11. |
- Svalkvist, Angelica, et al.
(författare)
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Investigation of the effect of varying scatter-to-primary ratios on nodule contrast in chest tomosynthesis
- 2011
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Ingår i: Medical Imaging 2011. - : SPIE - International Society for Optical Engineering. - 9780819485038 ; 7961
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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 %.
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| 12. |
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| 13. |
- Ullman, Gustaf, et al.
(författare)
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A Monte Carlo-based model for simulation of digital chest tomosynthesis
- 2010
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Ingår i: Radiation Protection Dosimetry. - Oxford : Oxford University Press. - 0144-8420 .- 1742-3406. ; 139:1-3, s. 159-163
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Ullman, Gustaf, et al.
(författare)
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A search for optimal x‐ray spectra in iodine contrast media mammography
- 2005
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Ingår i: Physics in medicine and biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 50:13, s. 3143-3152
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 15. |
- Ullman, Gustaf, et al.
(författare)
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Calculation of images from an anthropomorphic chest phantom using Monte Carlo methods
- 2006
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Ingår i: Proceedings of SPIE. - : SPIE.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 16. |
- Ullman, Gustav, et al.
(författare)
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Comparison of clinical and physical measures of image quality in chest PA and pelvis AP views at varying tube voltages
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 17. |
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| 18. |
- Ullman, Gustaf, et al.
(författare)
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Distributions of scatter to primary ratios and signal to noise ratios per pixel in digital chest imaging
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 355-358
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Ullman, Gustav, et al.
(författare)
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Distributions of scatter-to-primary ratios in chest PA radiography using grid or air gap for scatter-rejection
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 20. |
- Ullman, Gustav, et al.
(författare)
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Implementation of pathologies in the Monte Carlo model in chest and breast imaging
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 21. |
- Ullman, Gustav, et al.
(författare)
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On the extent of quantum noise limitation in digital chest radiography
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 22. |
- Ullman, Gustav, et al.
(författare)
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Optimisation of chest radiology by computer modelling of image quality measures and patient effective dose
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 23. |
- Ullman, Gustaf, et al.
(författare)
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Towards optimization in digital chest radiography using Monte Carlo modelling
- 2006
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Ingår i: Physics in medicine and biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 51:11, s. 2729-2743
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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