| 1. |
- Båth, Magnus, 1974, et al.
(author)
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Nodule detection in digital chest radiography: introduction to the RADIUS chest trial.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 85-91
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Journal article (peer-reviewed)abstract
- Most digital radiographic systems of today have wide latitude and are hence able to provide images with a small constraint on dose level. This opens up for an unprejudiced dose optimisation. However, in order to succeed in the optimisation task, good knowledge of the imaging and detection processes is needed. As a part of the European-wide research project 'unification of physical and clinical requirements for medical X-ray imaging'-governed by the Radiological Imaging Unification Strategies (RADIUS) Group-a major image quality trial was conducted by members of the group. The RADIUS chest trial was focused on the detection of lung nodules in digital chest radiography with the aims of determining to what extent (1) the detection of a nodule is dependent on its location, (2) the system noise disturbs the detection of lung nodules, (3) the anatomical noise disturbs the detection of lung nodules and (4) the image background and anatomical background act as pure noise for the detection of lung nodules. The purpose of the present paper is to give an introduction to the trial and describe the framework and set-up of the investigation.
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| 2. |
- Börjesson, Sara, et al.
(author)
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A software tool for increased efficiency in observer performance studies in radiology.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 45-52
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Journal article (peer-reviewed)abstract
- Observer performance studies are time-consuming tasks, both for the participating observers and for the scientists collecting and analysing the data. A possible way to optimise such studies is to perform them in a completely digital environment. A software tool-ViewDEX (Viewer for Digital Evaluation of X-ray images)-has been developed in Java, enabling it to function on almost any computer. ViewDEX is designed to handle several types of studies, such as visual grading analysis (VGA), image criteria scoring (ICS) and receiver operating characteristics (ROC). The results from each observer are saved in a log file, which can be exported for further analysis in, for example, a special software for analysing ROC results. By using ViewDEX for an ROC experiment, an evaluation rate of approximately 200 images per hour can be achieved, compared to approximately 25 images per hour using hard copy evaluation. The results are obtained within minutes of completion of the viewing. The risk of human errors in the process of data collection and analysis is also minimised. The viewer has been used in a major trial containing approximately 2700 images.
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| 3. |
- Hemdal, Bengt, et al.
(author)
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Can the average glandular dose in routine digital mammography screening be reduced? A pilot study using revised image quality criteria.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 383-8
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Journal article (peer-reviewed)abstract
- There is a need for tools that in a simple way can be used for the evaluation of image quality related to clinical requirements in mammography. The aim of this work was to adjust the present European image quality criteria to be relevant also for digital mammography images, and to use as simple and as few criteria as possible. A pilot evaluation of the new set of criteria was made with mammograms of 28 women from a General Electric Senographe 2000D full-field digital mammography system. One breast was exposed using the standard automatic exposure mode, the other using about half of that absorbed dose. Three experienced radiologists evaluated the images using visual grading analysis technique. The results indicate that the new quality criteria can be used for the evaluation of image quality related to clinical requirements in digital mammography in a simple way. The results also suggest that absorbed doses for the mammography system used may be substantially reduced.
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| 4. |
- Hemdal, Bengt, et al.
(author)
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Clinical evaluation of a new set of image quality criteria for mammography.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 389-94
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Journal article (peer-reviewed)abstract
- The European Commission (EC) quality criteria for screen-film mammography are used as a tool to assess image quality. A new set of criteria was developed and initially tested in a previous study. In the present study, these criteria are further evaluated using screen-film mammograms that have been digitised, manipulated to simulate different image quality levels and reprinted on film. Expert radiologists have evaluated these manipulated images using both the original (EC) and the new criteria. A comparison of three different simulated dose levels reveals that the new criteria yield a larger separation of image criteria scores than the old ones. These results indicate that the new set of image quality criteria has a higher discriminative power than the old set and thus seems to be more suitable for evaluation of image quality in mammography.
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| 5. |
- Håkansson, Markus, et al.
(author)
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Nodule detection in digital chest radiography: summary of the RADIUS chest trial.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 114-20
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Journal article (peer-reviewed)abstract
- As a part of the Europe-wide research project 'Unification of physical and clinical requirements for medical X-ray imaging'-governed by the Radiological Imaging Unification Strategies (RADIUS) Group-a major image quality trial was conducted by members of the group. The RADIUS chest trial aimed at thoroughly examining various aspects of nodule detection in digital chest radiography, such as the effects of nodule location, system noise, anatomical noise, and anatomical background. The main findings of the RADIUS chest trial concerning the detection of a lung nodule with a size in the order of 10 mm can be summarised as: (1) the detectability of the nodule is largely dependent on its location in the chest, (2) the system noise has a minor impact on the detectability at the dose levels used today, (3) the disturbance of the anatomical noise is larger than that of the system noise but smaller than that of the anatomical background and (4) the anatomical background acts as noise to a large extent and is the major image component affecting the detectability of the nodule.
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| 6. |
- Ruschin, Mark, et al.
(author)
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Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies.
- 2007
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In: Medical physics. - : Wiley. - 0094-2405. ; 34:2, s. 400-7
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Journal article (peer-reviewed)abstract
- The purpose of this study was to evaluate the effect of dose reduction in digital mammography on the detection of two lesion types-malignant masses and clusters of microcalcifications. Two free-response observer studies were performed-one for each lesion type. Ninety screening images were retrospectively selected; each image was originally acquired under automatic exposure conditions, corresponding to an average glandular dose of 1.3 mGy for a standard breast (50 mm compressed breast thickness with 50% glandularity). For each study, one to three simulated lesions were added to each of 40 images (abnormals) while 50 were kept without lesions (normals). Two levels of simulated system noise were added to the images yielding two new image sets, corresponding to simulated dose levels of 50% and 30% of the original images (100%). The manufacturer's standard display processing was subsequently applied to all images. Four radiologists experienced in mammography evaluated the images by searching for lesions and marking and assigning confidence levels to suspicious regions. The search data were analyzed using jackknife free-response (JA-FROC) methodology. For the detection of masses, the mean figure-of-merit (FOM) averaged over all readers was 0.74, 0.71, and 0.68 corresponding to dose levels of 100%, 50%, and 30%, respectively. These values were not statistically different from each other (F= 1.67, p=0.19) but showed a decreasing trend. In contrast, in the microcalcification study the mean FOM was 0.93, 0.67, and 0.38 for the same dose levels and these values were all significantly different from each other (F = 109.84, p < 0.0001). The results indicate that lowering the present dose level by a factor of two compromised the detection of microcalcifications but had a weaker effect on mass detection.
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| 7. |
- Ruschin, Mark, et al.
(author)
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Improved in-plane visibility of tumors using breast tomosynthesis
- 2007
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In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422 .- 1042-4687. ; 6510
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Journal article (other academic/artistic)abstract
- The purpose of this work was to evaluate and compare the visibility of simulated tumors in 2D digital mammography (DM) and breast tomosynthesis (BT) images of patients. Images of the same women were acquired on both a DM system (Mammomat Novation, Siemens) and a BT prototype system adapted from the same type of DM system. Using the geometrical properties of the two systems, simulated, ellipsoid-shaped tumors (average dimension: 8.4 mm × 6.6 mm × 5 mm) with irregular margins were projected and added to each DM image as well as each BT projection image prior to 3D reconstruction. The same beam quality and approximately the same total absorbed dose were used for each breast image acquisition on both systems. Two simulated tumors were added to each of thirty patient scans, yielding sixty cases. A series of 4-alternative forced choice (4-AFC) human observer experiments were conducted in order to determine what projected signal intensity (contrast) of the tumors in the DM images would be needed to achieve the same detectability as in the reconstructed BT images. Nine observers participated. For the BT 4-AFC experiment, when the signal intensity of the tumor on the central projection was 0.010 (natural logarithmic units) the mean percent of correct responses (PC) was measured to be 81.5%, which converted to a detectability index value (d') of 1.96. For the DM system, the same detectability was achieved at a signal intensity determined to be 0.038. Equivalent levels of tumor detection in BT images were thus achieved at around four times less projected signal intensity than in DM images, indicating that the use of BT may lead to earlier detection of breast cancer.
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| 8. |
- Ruschin, Mark, et al.
(author)
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Threshold pixel size for shape determination of microcalcifications in digital mammography: a pilot study.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 415-23
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Journal article (peer-reviewed)abstract
- The effect of pixel size on shape determination in screening digital mammography systems was studied using a shape identification task as the measured outcome. Ten microcalcifications on screen-films were digitised to a range of pixel sizes (2.5-200 microm) and extracted from computed radiography (CR) images (50 microm) acquired under equivalent imaging conditions. Fifteen observers attempted to identify the shape of each microcalcification at each pixel size. The results were collated to provide a fraction of correct responses vs. pixel size curve for each microcalcification. Averaging over all shapes, pixel values >100 microm lead to a significant decrease in shape determination ability (p < 0.01) for digitised screen-film. For CR images, half the shapes were not properly identified. Hence, although 20-100 microm was sufficient for microcalcification shape determination for digitised screen-film images, 50 microm was only borderline sufficient for the CR digital images.
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| 9. |
- Ruschin, Mark, et al.
(author)
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Using simple mathematical functions to simulate pathological structures--input for digital mammography clinical trial.
- 2005
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In: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 424-31
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Journal article (peer-reviewed)abstract
- In this study a set of structures has been simulated to represent a range of clinically relevant breast cancer mammographic lesions including solid tumours and microcalcifications. All structures have been created using simple random-based mathematical functions and have been inserted into a subset of digital mammography images at appropriate contrast levels into various regions of the breast, including dense fibroglandular and adipose tissue. These structures and their appearance in these clinical images were evaluated in terms of how realistic they looked. They will be used as the input to a large-scale clinical trial designed to examine the effect of significant dose reduction in digital mammography by comparing the detectability of such structures in images acquired at full and quarter automatic exposure control (AEC) dose level and in images with simulated noise levels in between.
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| 10. |
- Timberg, Pontus, et al.
(author)
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Impact of dose on observer performance in breast tomosynthesis using breast specimens
- 2008
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In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6913, s. 9134-9134
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Journal article (other academic/artistic)abstract
- The purpose of this study was to investigate the effect of dose on lesion detection† and characterization in breast tomosynthesis (BT), using human breast specimens. Images of 27 lesions in breast specimens were acquired on a BT prototype‡ based on a Mammomat Novation (Siemens) full-field digital mammography (FFDM) system. Two detector modes - binned (2×1 in the scan direction) and full resolution - and four BT exposure levels - approximately 2×, 1.5×, 1×, and 0.5× the total mAs at the same beam quality as used in a single FFDM view with a Mammomat Novation unit under automatic exposure control (AEC) conditions - were examined. The exposure for all BT scans was equally divided among 25 projections. An enhanced filtered back projection reconstruction method was applied with a constant filter setting. A human observer performance study was conducted in which the observers were forced to select the minimum (threshold) exposure level at which each lesion could be both detected and characterized for assessment of recall or not in a screening situation. The median threshold exposure level for all observers and all lesions corresponded to approximately 1×, which is half the exposure of what we currently use for BT. A substantial variation in exposure thresholds was noticed for different lesion types. For low contrast lesions with diffuse borders, an exposure threshold of approximately 2× was required, whereas for spiculated high contrast lesions and lesions with well defined borders, the exposure threshold was lower than 0.5×. The use of binned mode had no statistically significant impact on observer performance compared to full resolution mode. There was no substantial difference between the modes for the detection and characterization of the lesion types.
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