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ABSTRACT: Purpose: To evaluate intra- and interobserver variability, as well as agreement for nodule size measurements on chest tomosynthesis and computed tomographic (CT) images. Materials and Methods: The Regional Ethical Review Board approved this study, and all participants gave written informed consent. Thirty-six segmented nodules in 20 patients were included in the study. Eight observers measured the left-to-right, inferior-to-superior, and longest nodule diameters on chest tomosynthesis and CT images. Intra- and interobserver repeatability, as well as agreement between measurements on chest tomosynthesis and CT images, were assessed as recommended by Bland and Altman. Results: The difference between the mean manual and the segmented diameter was -2.2 and -2.3 mm for left-to-right and -2.6 and -2.2 mm for the inferior-to-superior diameter for measurements on chest tomosynthesis and CT images, respectively. Intraobserver 95% limits of agreement (LOA) for the longest diameter ranged from a lower limit of -1.1 mm and an upper limit of 1.0 mm to -1.8 and 1.8 mm for chest tomosynthesis and from -0.6 and 0.9 mm to -3.1 and 2.2 mm for axial CT. Interobserver 95% LOA ranged from -1.3 and 1.5 mm to -2.0 and 2.1 mm for chest tomosynthesis and from -1.8 and 1.1 mm to -2.2 and 3.1 mm for axial CT. The 95% LOA concerning the mean of the observers' measurements of the longest diameter at chest tomosynthesis and axial CT were ±2.1 mm (mean measurement error, 0 mm). For the different observers, the 95% LOA between the modalities ranged from -2.2 and 1.6 mm to -3.2 and 2.8 mm. Conclusion: Measurements on chest tomosynthesis and CT images are comparable, because there is no evident bias between the modalities and the repeatability is similar. The LOA between measurements for the two modalities raise concern if measurements from chest tomosynthesis and CT were to be used interchangeably. © RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12111459/-/DC1.
Radiology 10/2012; 265(1):273-82. · 5.73 Impact Factor
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Angelica Svalkvist,
Ase Allansdotter Johnsson,
Jenny Vikgren,
Markus Håkansson,
Gustaf Ullman,
Marianne Boijsen,
Valeria Fisichella,
Agneta Flinck,
David Molnar,
Lars Gunnar Månsson, Magnus Båth
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ABSTRACT: 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. Purpose 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. Material 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. Results 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). Conclusion 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.
Acta Radiologica 07/2012; 53(8):874-84. · 1.37 Impact Factor
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ABSTRACT: This study contributes to social studies of imaging and visualization practices within scientific and medical settings. The focus is on practices in radiology, which are bound up with visual records known as radiographs. The study addresses work following the introduction of a new imaging technology, tomosynthesis. Since it was a novel technology, there was limited knowledge of how to correctly analyse tomosynthesis images. To address this problem, a collective review session was arranged. The purpose of the present study was to uncover the practical work that took place during that session and to show how, and on what basis, new methods, interpretations and understandings were being generated. The analysis displays how the diagnostic work on patients' bodies was grounded in two sets of technologically produced renderings. This shows how expertise is not simply a matter of providing correct explanations, but also involves discovery work in which visual renderings are made transparent. Furthermore, the results point to how the disciplinary knowledge is intertwined with timely actions, which in turn, partly rely on established practices of manipulating and comparing images. The embodied and situated reasoning that enabled radiologists to discern objects in the images thus display expertise as inherently practical and domain-specific.
Social Studies of Science 12/2011; 41(6):867-91. · 1.50 Impact Factor
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Sara Asplund,
Ase A Johnsson,
Jenny Vikgren,
Angelica Svalkvist,
Marianne Boijsen,
Valeria Fisichella,
Agneta Flinck,
Asa Wiksell,
Jonas Ivarsson,
Hans Rystedt,
Lars Gunnar Månsson,
Susanne Kheddache, Magnus Båth
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ABSTRACT: In chest tomosynthesis, low-dose projections collected over a limited angular range are used for reconstruction of an arbitrary number of section images of the chest, resulting in a moderately increased radiation dose compared to chest radiography.
To investigate the effects of learning with feedback on the detection of pulmonary nodules for observers with varying experience of chest tomosynthesis, to identify pitfalls regarding detection of pulmonary nodules, and present suggestions for how to avoid them, and to adapt the European quality criteria for chest radiography and computed tomography (CT) to chest tomosynthesis.
Six observers analyzed tomosynthesis cases for presence of nodules in a jackknife alternative free-response receiver-operating characteristics (JAFROC) study. CT was used as reference. The same tomosynthesis cases were analyzed before and after learning with feedback, which included a collective learning session. The difference in performance between the two readings was calculated using the JAFROC figure of merit as principal measure of detectability.
Significant improvement in performance after learning with feedback was found only for observers inexperienced in tomosynthesis. At the collective learning session, localization of pleural and subpleural nodules or structures was identified as the main difficulty in analyzing tomosynthesis images.
The results indicate that inexperienced observers can reach a high level of performance regarding nodule detection in tomosynthesis after learning with feedback and that the main problem with chest tomosynthesis is related to the limited depth resolution.
Acta Radiologica 06/2011; 52(5):503-12. · 1.37 Impact Factor
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Sara Asplund,
Åse A Johnsson,
Jenny Vikgren,
Angelica Svalkvist,
Marianne Boijsen,
Valeria Fisichella,
Agneta Flinck,
Åsa Wiksell,
Jonas Ivarsson,
Hans Rystedt,
Lars Gunnar Månsson,
Susanne Kheddache, Magnus Båth
Acta Radiologica. 01/2011; 52:503-512.
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ABSTRACT: The DICOM part 14 greyscale standard display function provides one way of harmonising image appearance under different monitor luminance settings. This function is based on ideal observer conditions, where the eye is always adapted to the target luminance and thereby also at peak contrast sensitivity. Clinical workstations are, however, often submitted to variations in ambient light due to a sub-optimal reading room light environment. Also, clinical images are inhomogeneous and low-contrast patterns must be detected even at luminance levels that differ from the eye adaptation level. All deviations from ideal luminance conditions cause the observer to detect patterns with reduced eye sensitivity but the magnitude of this reduction is unclear. A method is presented to display well-defined sinusoidal low-contrast test patterns on an liquid crystal display. The observers were exposed to light from three different areas: (i) the test pattern covering approximately 2 degrees x 2 degrees; (ii) the remaining of the display surface and (iii) ambient light from outside the display area covering most of the observers' field of view. By adjusting the luminance from each of these three areas, the observers' ability to detect low-contrast patterns under sub-optimal viewing conditions was studied. Ambient light from outside the display area has a moderate effect on the contrast threshold, except for the combination of high ambient light and dark objects, where the contrast threshold increased considerably.
Radiation Protection Dosimetry 03/2010; 139(1-3):62-70. · 0.82 Impact Factor
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ABSTRACT: With the increasing use of computed tomography (CT) for urography examinations, the indications for 'conventional' projection urography have changed and are more focused on high-contrast details. The purpose of the present study was to optimise the beam quality for urography examinations performed with a Gd(2)O(2)S:Tb flat-panel detector for the new conditions. Images of an anthropomorphic phantom were collected at different tube voltages with a CXDI-40G detector (Canon Inc., Tokyo, Japan). The images were analysed by radiologists and residents in a visual grading characteristics (VGCs) study. The tube voltage resulting in the best image quality was 55 kV, which therefore was selected for a clinical study. Images from 62 patients exposed with either 55 or 73 kV (original tube voltage) at constant effective doses were included. The 55-kV images underwent simulated dose reduction to represent images collected at 80, 64, 50, 40 and 32 % of the original dose level. All images were included in a VGC study where the observers rated the visibility of important anatomical landmarks. For images collected at 55 kV, an effective dose of approximately 85 % resulted in the same image quality as for images collected at 73 kV at 100 % dose. In conclusion, a low tube voltage should be used for conventional urography focused on high-contrast details. The study indicates that using a tube voltage of 55 kV instead of 73 kV for a Gd(2)O(2)S:Tb flat-panel detector, the effective dose can be reduced by approximately 10-20 % for normal-sized patients while maintaining image quality.
Radiation Protection Dosimetry 03/2010; 139(1-3):86-91. · 0.82 Impact Factor
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ABSTRACT: Chest tomosynthesis, which refers to the principle of collecting low-dose projections of the chest at different angles and using these projections to reconstruct section images of the chest, is an imaging technique recently introduced to health care. The main purpose of the present work was to determine the average effective dose to patients from clinical use of chest tomosynthesis. Exposure data for two chest radiography laboratories with tomosynthesis option (Definium 8000 with VolumeRAD option, GE Healthcare, Chalfont St. Giles, UK) were registered for 20 patients with a weight between 60 and 80 kg (average weight of 70.2 kg). The recorded data were used in the Monte Carlo program PCXMC 2.0 (STUK-Radiation and Nuclear Safety Authority, Helsinki, Finland) to determine the average effective dose for each projection. The effective dose for the chest tomosynthesis examination, including a scout view and the tomosynthesis acquisition, was finally obtained by adding the effective doses from all projections. Using the weighting factors given in ICRP 103, the average effective dose for the examination was found to be 0.13 mSv, whereas the average effective dose for the conventional two-view chest radiography examination was 0.05 mSv. A conversion factor of 0.26 mSv Gy(-1) cm(-2) was found suitable for determining the effective dose from a VolumeRAD chest tomosynthesis examination from the total registered kerma-area product. In conclusion, the effective dose to a standard-sized patient (170 cm/70 kg) from a VolumeRAD chest tomosynthesis examination is ~2 % of an average chest CT and only two to three times the effective dose from the conventional two-view chest radiography examination.
Radiation Protection Dosimetry 03/2010; 139(1-3):153-8. · 0.82 Impact Factor
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ABSTRACT: The purpose of the present work was to describe a method of using an imaging plate from a computed radiography system to determine the computed tomography (CT) dose profile (the tritium method) and to compare this method with point-dose measurements using a solid-state detector (CT Dose Profiler; RTI Electronics, Mölndal, Sweden) and the indirect method of comparing the air kerma-length product (P(KL)) at different beam collimations. The three methods were used to determine the full width at half maximum (FWHM) of the dose profile of a multi-slice CT at different nominal beam collimations. For all beam collimations, the obtained deviation between the tritium method and the CT Dose Profiler was smaller than 0.1 mm. The maximum relative error was 2 %. For the P(KL) method, the deviation from the CT Dose Profiler was between 0.2 and 0.4 mm, resulting in a relative error larger than 10 % for the smallest beam collimation even after normalisation to a known FWHM. In conclusion, the proposed method of using an imaging plate to determine the FWHM of the CT dose profile has a high accuracy and shows good agreement with the more advanced method of point-dose measurements using a solid-state detector.
Radiation Protection Dosimetry 03/2010; 139(1-3):434-8. · 0.82 Impact Factor
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ABSTRACT: The aims of this work were to explore the dosimetry of chest tomosynthesis and to determine conversion factors between air kerma-area product (KAP) and the effective dose for different system configurations and patient sizes. Tomosynthesis systems were modelled with different angular intervals and tube voltages for the collection of the projection images as well as different distributions of the total exposure over the projections. The Monte Carlo-based computer software PCXMC developed by STUK (Radiation and Nuclear Safety Authority in Finland) was used to calculate the effective doses for each modelled tomosynthesis system for various patient sizes. The conversion factor between KAP and effective dose was obtained both for the zero-degree projection alone and for the entire tomosynthesis examination for each system configuration and patient size. The results reveal that the conversion factor for the zero-degree projection can be used to estimate the total effective dose from a tomosynthesis examination with acceptable accuracy, leading to an error smaller than 10 % irrespective of the system configuration and patient size. For higher accuracy, conversion factors between the total KAP and the total effective dose that take the angular interval and exposure configuration into account are presented for each system.
Radiation Protection Dosimetry 03/2010; 139(1-3):144-52. · 0.82 Impact Factor
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ABSTRACT: The development of investigation techniques, image processing, workstation monitors, analysing tools etc. within the field of radiology is vast, and the need for efficient tools in the evaluation and optimisation process of image and investigation quality is important. ViewDEX (Viewer for Digital Evaluation of X-ray images) is an image viewer and task manager suitable for research and optimisation tasks in medical imaging. ViewDEX is DICOM compatible and the features of the interface (tasks, image handling and functionality) are general and flexible. The configuration of a study and output (for example, answers given) can be edited in any text editor. ViewDEX is developed in Java and can run from any disc area connected to a computer. It is free to use for non-commercial purposes and can be downloaded from http://www.vgregion.se/sas/viewdex. In the present work, an evaluation of the efficiency of ViewDEX for receiver operating characteristic (ROC) studies, free-response ROC (FROC) studies and visual grading (VG) studies was conducted. For VG studies, the total scoring rate was dependent on the number of criteria per case. A scoring rate of approximately 150 cases h(-1) can be expected for a typical VG study using single images and five anatomical criteria. For ROC and FROC studies using clinical images, the scoring rate was approximately 100 cases h(-1) using single images and approximately 25 cases h(-1) using image stacks ( approximately 50 images case(-1)). In conclusion, ViewDEX is an efficient and easy-to-use software for observer performance studies.
Radiation Protection Dosimetry 03/2010; 139(1-3):42-51. · 0.82 Impact Factor
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ABSTRACT: The purpose of the present study was to investigate if the exposure could be reduced from the clinical setting (resulting in an effective dose of 8 microSv for a neonate of weight 0.7 kg and height 25 cm at a tube voltage of 90 kV) without negatively influencing the image quality for a dual-side readout technique computed radiography (CR) system in chest radiography of premature neonates. Chest radiographs of premature neonates were acquired with the double-side readout technique CR system. The images underwent simulated dose reduction in steps of 20 % to represent five different radiation dose levels. Four image quality criteria, related to the visibility of important anatomical structures, were used in a visual grading study where five experienced radiologists rated how well the criteria were fulfilled for all images. When reducing the radiation dose, a decrease in image quality could be observed already at the 80 % dose level for all the structures. The results indicate that a decrease in exposure from the clinically used setting affects the image quality negatively for the CR system.
Radiation Protection Dosimetry 03/2010; 139(1-3):275-80. · 0.82 Impact Factor
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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 degrees. 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.
Radiation Protection Dosimetry 03/2010; 139(1-3):159-63. · 0.82 Impact Factor
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ABSTRACT: The purpose of the present work was to investigate the validity of using the Monte Carlo technique for determining the detective quantum efficiency (DQE) of a gamma camera system and to use this technique in investigating the DQE behaviour of a gamma camera system and its dependency on a number of relevant parameters. The Monte Carlo-based software SIMIND, simulating a complete gamma camera system, was used in the present study. The modulation transfer function (MTF) of the system was determined from simulated images of a point source of (99m)Tc, positioned at different depths in a water phantom. Simulations were performed using different collimators and energy windows. The MTF of the system was combined with the photon yield and the sensitivity, obtained from the simulations, to form the frequency-dependent DQE of the system. As figure-of-merit (FOM), the integral of the 2D DQE was used. The simulated DQE curves agreed well with published data. As expected, there was a strong dependency of the shape and magnitude of the DQE curve on the collimator, energy window and imaging position. The highest FOM was obtained for a lower energy threshold of 127 keV for objects close to the detector and 131 keV for objects deeper in the phantom, supporting an asymmetric window setting to reduce scatter. The Monte Carlo software SIMIND can be used to determine the DQE of a gamma camera system from a simulated point source alone. The optimal DQE results in the present study were obtained for parameter settings close to the clinically used settings.
Radiation Protection Dosimetry 02/2010; 139(1-3):219-27. · 0.82 Impact Factor
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Magnus Båth
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ABSTRACT: There are many ways in which imaging systems can be evaluated. The aim of the present paper is to provide an overview of a number of selected approaches to evaluating imaging systems, often encountered by the medical physicist, and discuss their validity and reliability. Specifically, it will cover (i) characterisation of an imaging system in terms of its detective quantum efficiency using linear-systems analysis; (ii) attempts to calculate relevant measures directly in images using the Rose model and the pixel signal-to-noise ratio; (iii) task-based methods incorporating human observers such as receiver-operating characteristics and (iv) visual grading-based methods using experienced radiologists as observers.
Radiation Protection Dosimetry 02/2010; 139(1-3):26-36. · 0.82 Impact Factor
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ABSTRACT: Adding noise to clinical radiographs to simulate dose reduction can be used to investigate the relationship between dose level and clinical image quality without exposing patients to additional radiation. The purpose of the present paper was to examine the benefits of using a method that accounts for detective quantum efficiency (DQE) variations that may occur in different dose ranges in the simulated dose reduction process. A method initially intended for simulated dose reduction in tomosynthesis was applied to extremely low-dose posterioanterior radiographs of an anthropomorphic chest phantom, selected from a group of projection images included in a tomosynthesis examination and compared with a previous method that do not account for DQE variations. A comparison of images simulated to be collected at a lower dose level (73 % of the original dose level) and images actually collected at this lower dose level revealed that the error in the integrated normalised noise power spectrum was smaller than 4 % for the method that accounts for DQE variations in the simulated dose reduction, whereas the error was larger than 20 % for the previous method. This indicates that an increased validity in dose reduction simulation of digital radiographic systems is obtained with a method accounting for DQE variations.
Radiation Protection Dosimetry 02/2010; 139(1-3):57-61. · 0.82 Impact Factor
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ABSTRACT: According to European and national legislation, as well as international recommendations, X-ray examinations shall be optimised. However, with limited resources and hundreds of different types of X-ray examinations, it may be difficult to prioritise among the optimisation tasks at a radiology department. This work is focused on describing a method that can be used to determine the order of which the examinations should be optimised. In the Medical Exposure Directive from 1997, the European Commission prescribes the content of an optimisation process in relation to medical exposure. A reasonable interpretation of the directive is that the assurance of medical purpose for a justified examination is superior to the need of decreased radiation dose. This was used as a basis for developing a method for prioritisation among optimisation tasks. For each examination type, the following four yes/no questions are raised: (i) Is the present image quality unacceptable? (ii) Is the examination of particular importance? (iii) Is the radiation dose suspiciously high? (iv) Are there special dose level concerns, e.g. diagnostic reference levels? Arguing that a positive response to any of the four questions results in the examination being higher prioritised than otherwise and that the questions are labelled in order of decreasing relevance, it can be shown that the resulting flow chart, determining the order of which the examinations should be optimised, can be described by a 4-bit binary scale. In this way, each examination type is given a number from 0 to 15, a higher number corresponding to the examination being prioritised higher in the optimisation work. The method was applied to a general radiology department and resulted in a well-discriminated distribution of examinations prioritised for optimisation tasks. In conclusion, taking into account both medical outcome and potential risk, the proposed method can be used to determine the order in which examinations at a radiology department should be optimised.
Radiation Protection Dosimetry 02/2010; 139(1-3):393-9. · 0.82 Impact Factor
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ABSTRACT: The aim of the present study was to evaluate the use of common external image processing to compensate for differences in appearance between digital X-ray images from different vendors. Twenty posteroanterior chest radiographs were collected from each of three different modalities from different vendors (GE, Siemens and Canon) with vendor-specific image processing applied. The images were also extracted with neutral process parameters and processed with external image-processing software. Six experienced radiologists rated the quality and the similarity of the images with the original Siemens images. The externally processed GE images were rated of higher quality than the original GE images and more similar to the original Siemens images (p < 0.001). The opposite was obtained for the Canon images. The externally processed Siemens images were rated of similar quality as the original images. The present study indicates the possibility of using common external image processing to harmonise the appearance of images from different vendors, although the exposure parameters may need to be adjusted for individual vendors.
Radiation Protection Dosimetry 02/2010; 139(1-3):92-7. · 0.82 Impact Factor
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ABSTRACT: The purpose of the present work was to investigate the reliability of subjective assessments of the low-contrast visibility in constancy control of computed tomography (CT). Axial CT images of a low-contrast phantom were acquired on an 8-slice multi-detector CT scanner at nine tube current settings ranging from 75 to 440 mA. Five medical physicists assessed the visibility of the low-contrast details in two sessions. In the first session, containing 54 images, the visibility was rated on an absolute scale by determining the number of visible details in each contrast group in each image. In the second session, 180 image pairs were presented to the observers with the task of determining if the two images had been acquired under identical conditions or not. In the absolute session, both the intra- and inter-observer variabilities were high. In the relative session, the variability was smaller, but an exposure difference of 50 % was needed for all observers to correctly identify a change in all cases. In conclusion, the present study indicates that subjective assessments of the low-contrast visibility in constancy control of CT are not reliable.
Radiation Protection Dosimetry 02/2010; 139(1-3):449-54. · 0.82 Impact Factor
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ABSTRACT: Methods for simulating dose reduction are valuable tools in the work of optimizing radiographic examinations. Using such methods, clinical images can be simulated to have been collected at other, lower, dose levels without the need of additional patient exposure. A recent technology introduced to healthcare that needs optimization is tomosynthesis, where a number of low-dose projection images collected at different angles is used to reconstruct section images of an imaged object. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems, suitable for tomosynthesis.
The developed method uses information about the noise power spectrum (NPS) at the original dose level and the simulated dose level to create a noise image that is added to the original image to produce an image that has the same noise properties as an image actually collected at the simulated dose level. As the detective quantum efficiency (DQE) of digital detectors operating at the low dose levels used for tomosynthesis may show a strong dependency on the dose level, it is important that a method for simulating dose reduction for tomosynthesis takes this dependency into account. By applying an experimentally determined relationship between pixel mean and pixel variance, variations in both dose and DQE in relevant dose ranges are taken into account.
The developed method was tested on a chest tomosynthesis system and was shown to produce NPS of simulated dose-reduced projection images that agreed well with the NPS of images actually collected at the simulated dose level. The simulated dose reduction method was also applied to tomosynthesis examinations of an anthropomorphic chest phantom, and the obtained noise in the reconstructed section images was very similar to that of an examination actually performed at the simulated dose level.
In conclusion, the present article describes a method for simulating dose reduction suitable for tomosynthesis. However, the method applies equally well to any digital radiographic system, although the benefits of correcting for DQE variations may be smaller.
Medical Physics 01/2010; 37(1):258-69. · 2.83 Impact Factor
