| 1. |
- Almén, Anja, 1964, et al.
(författare)
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A CONCEPTUAL FRAMEWORK FOR MANAGING RADIATION DOSE TO PATIENTS IN DIAGNOSTIC RADIOLOGY USING REFERENCE DOSE LEVELS
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 17-23
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Tidskriftsartikel (refereegranskat)abstract
- The overall aim of the present work was to develop a conceptual framework for managing radiation dose in diagnostic radiology with the intention to support optimisation. An optimisation process was first derived. The framework for managing radiation dose, based on the derived optimisation process, was then outlined. The outset of the optimisation process is four stages: providing equipment, establishing methodology, performing examinations and ensuring quality. The optimisation process comprises a series of activities and actions at these stages. The current system of diagnostic reference levels is an activity in the last stage, ensuring quality. The system becomes a reactive activity only to a certain extent engaging the core activity in the radiology department, performing examinations. Three reference dose levels-possible, expected and established-were assigned to the three stages in the optimisation process, excluding ensuring quality. A reasonably achievable dose range is also derived, indicating an acceptable deviation from the established dose level. A reasonable radiation dose for a single patient is within this range. The suggested framework for managing radiation dose should be regarded as one part of the optimisation process. The optimisation process constitutes a variety of complementary activities, where managing radiation dose is only one part. This emphasises the need to take a holistic approach integrating the optimisation process in different clinical activities.
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| 2. |
- Almén, Anja, et al.
(författare)
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Challenges assessing radiation risk in image-guided treatments-implications on optimisation of radiological protection
- 2018
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Ingår i: Journal of Radiological Protection. - : IOP Publishing. - 0952-4746 .- 1361-6498. ; 38:3, s. 1064-1076
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Tidskriftsartikel (refereegranskat)abstract
- The present work explores challenges when assessing organ dose and effective dose concerning image-guided treatments. During these treatments considerable x-ray imaging is employed using technically advanced angiographic x-ray equipment. Thus, the radiation dose to organs and the related radiation risk are relatively difficult to assess. This has implications on the optimisation process, in which assessing radiation dose is one important part. In this study, endovascular aortic repair treatments were investigated. Organ dose and effective dose were assessed using Monte Carlo calculations together with a detailed specification of the exposure situation and patient size. The resulting normalised organ dose and effective dose with respect to kerma-area product for patient sizes and radiation qualities representative for the patient group were evaluated. The variability and uncertainty were investigated and their possible impact on optimisation of radiation protection was discussed. Exposure parameters, source to detector distances etc varied between treatments and also varied between image acquisitions during one treatment. Thus the derived normalised organ dose and effective dose exhibited a large range of values depending greatly on used exposure parameters and patient configuration. The derived normalised values for effective dose varied approximately between 0.05 and 0.30 mSv per Gy.cm(2) when taking patient sizes and exposure parameters into consideration, the values for organ doses exhibited even larger variation. The study shows a possible systematic error for derived organ doses and effective dose up to a factor of 7 if detailed exposure or patient characteristics are not known and/or not taken into consideration. The intra-treatment variability was also substantial and the normalised dose values varied up to a factor of 2 between image acquisitions during one treatment. The study shows that the use of conversion factors that are not adapted to the clinic can cause the radiation dose to be exaggerated or underestimated considerably. A conclusion from the present study is that the systematic error could be large and should be estimated together with random errors. A large uncertainty makes it difficult to detect true differences in radiation dose between methods and technology-a prerequisite for optimising radiation protection for image-guided treatments.
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| 3. |
- Almén, Anja, 1964, et al.
(författare)
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OPTIMISATION OF OCCUPATIONAL RADIATION PROTECTION IN IMAGE-GUIDED INTERVENTIONS: EXPLORING VIDEO RECORDINGS AS A TOOL IN THE PROCESS
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 425-429
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Tidskriftsartikel (refereegranskat)abstract
- The overall purpose of this work was to explore how video recordings can contribute to the process of optimising occupational radiation protection in image-guided interventions. Video-recorded material from two image-guided interventions was produced and used to investigate to what extent it is conceivable to observe and assess dose-affecting actions in video recordings. Using the recorded material, it was to some extent possible to connect the choice of imaging techniques to the medical events during the procedure and, to a less extent, to connect these technical and medical issues to the occupational exposure. It was possible to identify a relationship between occupational exposure level to staff and positioning and use of shielding. However, detailed values of the dose rates were not possible to observe on the recordings, and the change in occupational exposure level from adjustments of exposure settings was not possible to identify. In conclusion, the use of video recordings is a promising tool to identify dose-affecting instances, allowing for a deeper knowledge of the interdependency between the management of the medical procedure, the applied imaging technology and the occupational exposure level. However, for a full information about the dose-affecting actions, the equipment used and the recording settings have to be thoroughly planned.
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| 4. |
- Almén, Anja, 1964, et al.
(författare)
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Optimisation of occupational radiological protection in image-guided interventions: potential impact of dose rate measurements.
- 2015
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Ingår i: Journal of radiological protection : official journal of the Society for Radiological Protection. - : IOP Publishing. - 1361-6498. ; 35:1, s. 47-62
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Tidskriftsartikel (refereegranskat)abstract
- The optimisation of occupational radiological protection is challenging and a variety of factors have to be considered. Physicians performing image-guided interventions are working in an environment with one of the highest radiation risk levels in healthcare. Appropriate knowledge about the radiation environment is a prerequisite for conducting the optimisation process. Information about the dose rate variation during the interventions could provide valuable input to this process. The overall purpose of this study was to explore the prerequisite and feasibility to measure dose rate in scattered radiation and to assess the usefulness of such data in the optimisation process.Using an active dosimeter system, the dose rate in the unshielded scattered radiation field was measured in a fixed point close to the patient undergoing an image-guided intervention. The measurements were performed with a time resolution of one second and the dose rate data was continuously timed in a data log. In two treatment rooms, data was collected during a 6month time period, resulting in data from 380 image-guided interventions and vascular treatments in the abdomen, arms and legs. These procedures were categorised into eight types according to the purpose of the treatment and the anatomical region involved.The dose rate varied substantially between treatment types, both regarding the levels and the distribution during the procedure. The maximum dose rate for different types of interventions varied typically between 5 and 100mSvh(-1), but substantially higher and lower dose rates were also registered. The average dose rate during a complete procedure was however substantially lower and varied typically between 0.05 and 1mSvh(-1). An analysis of the distribution disclosed that for a large part of the treatment types, the major amount of the total accumulated dose for a procedure was delivered in less than 10% of the exposure time and in less than 1% of the total procedure time.The present study shows that systematic dose rate measurements are feasible. Such measurements can be used to give a general indication of the exposure level to the staff and could serve as a first risk assessment tool when introducing new treatment types or x-ray equipment in the clinic. For example, it could provide an indication for when detailed eye dose measurements are needed. It also gives input to risk management considerations and the development of efficient routines for other radiological protection measures.
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| 5. |
- Almén, Anja, 1964, et al.
(författare)
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The process of optimisation of radiological protection – the significance of diagnostic reference levels
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The system of diagnostic reference levels in medicine has been presented as a tool to advice on when a local review of the procedures and equipment is warranted in order to determine whether the protection has been adequately optimised. The system is somewhat country specific, presumably due to different national regulations or guidelines, but as a whole relies on the same principles and standards. Diagnostic reference levels are typically set for standardised patients and procedures with minor considerations of the need to manage individual patient characteristics or specific medical tasks in the optimisation process. Optimisation of radiological protection should involve key aspects influencing the radiation dose to the patients and also include the needs of optimising the protection for each patient individually. The actual given radiation dose to the patient is affected by a number of factors, amongst other things equipment specific features and training of staff performing the examinations. This emphases the need to take a holistic approach and integrate different clinical processes - e.g. purchasing of equipment or the implementation of new examination protocols in the clinic – in the process of optimisation. Taking this approach gives the opportunity to evaluate the significance of the current system of diagnostic reference levels in the process of optimisation and to identify other reference levels supporting the process of optimisation. This paper will investigate the optimisation process and identify key instances where reference levels could provide support to the optimisation process. The issue of optimising the individual examination with regard to patient characteristics and medical indication will be specifically addressed.
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| 6. |
- Andersson, Peter, 1975, et al.
(författare)
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Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams
- 2023
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Ingår i: Biomedical Engineering & Physics Express. - : Institute of Physics. - 2057-1976. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Purpose. To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98-1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54-0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99-1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92-0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses. © 2023 The Author(s).
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| 7. |
- Arvidsson, Jonathan, 1986, et al.
(författare)
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Automated estimation of in-plane nodule shape in chest tomosynthesis images
- 2015
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Ingår i: International Federation for Medical and Biological Engineering Proceedings. - Cham : Springer International Publishing. - 1680-0737. - 9783319129679 ; 48, s. 20-23
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Konferensbidrag (refereegranskat)abstract
- The purpose of this study was to develop an automated segmentation method for lung nodules in chest tomo-synthesis images. A number of simulated nodules of different sizes and shapes were created and inserted in two different locations into clinical chest tomosynthesis projections. The tomosynthesis volumes were then reconstructed using standard cone beam filtered back projection, with 1 mm slice interval. For the in-plane segmentation, the central plane of each nodule was selected. The segmentation method was formulated as an optimization problem where the nodule boundary corresponds to the minimum of the cost function, which is found by dynamic programming. The cost function was composed of terms related to pixel intensities, edge strength, edge direction and a smoothness constraint. The segmentation results were evaluated using an overlap measure (Dice index) of nodule regions and a distance measure (Hausdorff distance) between true and segmented nodule. On clinical images, the nodule segmentation method achieved a mean Dice index of 0.96 ± 0.01, and a mean Hausdorff distance of 0.5 ± 0.2 mm for isolated nodules and for nodules close to other lung structures a mean Dice index of 0.95 ± 0.02 and a mean Hausdorff distance of 0.5 ± 0.2 mm. The method achieved an acceptable accuracy and may be useful for area estimation of lung nodules.
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| 8. |
- Arvidsson, Jonathan, et al.
(författare)
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Image Fusion of Reconstructed Digital Tomosynthesis Volumes From a Frontal and a Lateral Acquisition
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 410-415
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Tidskriftsartikel (refereegranskat)abstract
- Digital tomosynthesis (DTS) has been used in chest imaging as a low radiation dose alternative to computed tomography (CT). Traditional DTS shows limitations in the spatial resolution in the out-of-plane dimension. As a first indication of whether a dual-plane dual-view (DPDV) DTS data acquisition can yield a fair resolution in all three spatial dimensions, a manual registration between a frontal and a lateral image volume was performed. An anthropomorphic chest phantom was scanned frontally and laterally using a linear DTS acquisition, at 120 kVp. The reconstructed image volumes were resampled and manually co-registered. Expert radiologist delineations of the mediastinal soft tissues enabled calculation of similarity metrics in regard to delineations in a reference CT volume. The fused volume produced the highest total overlap, implying that the fused volume was a more isotropic 3D representation of the examined object than the traditional chest DTS volumes.
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| 9. |
- Arvidsson, Jonathan, et al.
(författare)
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Image fusion of two FBP-reconstructed digital tomosynthesis volumes from frontal and lateral acquisitions
- 2015
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Ingår i: Optimisation in X-ray and Molecular Imaging 2015 - the Fourth Malmö Conference on Medical Imaging, Gothenburg, Sweden, 28-30 May 2015.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: Digital tomosynthesis (DTS) has been used in chest imaging as a low radiation dose alternative to computed tomography (CT). DTS can to a certain degree separate overlapping anatomical structures at different depth levels using traditional filtered back projection (FBP) reconstruction schemes. However, the spatial resolution remains limited in the out-of-plane dimension. The aim of this work was to investigate if utilizing information from both a frontal and lateral DTS acquisition will give a more accurate 3D representation of the examined object. Method: As a first indication of whether a dual-view DTS data acquisition can yield a fair resolution in the three spatial dimensions, a manual registration between two reconstructed DTS volumes, one being a frontal data acquisition and the other a lateral one, was performed. An anthropomorphic chest phantom was scanned using a linear DTS acquisition in frontal and lateral directions, at 120 kVp. The two corresponding volumes where reconstructed, downsampled to a lower resolution and manually co-registered. Being manual, the registration step was subjective and thus included identifying suitable landmarks that could be used to ensure that the correct rigid transformation between the two volumes was found. Finally a CT examination of the phantom, used as a ground truth 3D representation, was manually co-registered to the DTS data. The reconstruction, downsampling and co-registering was performed using both commercial and freely available software. Major Findings: The resulting co-registered volume gave a more accurate isotropic 3D representation of the examined object than the two original reconstructions. Oblique planes were more accurately reproduced by the co-registered volume whereas coronal and sagittal planes were better reproduced by the original frontally and laterally reconstructed volumes. Conclusions: The proposed method shows that fusing frontally and laterally reconstructed DTS volumes is possible and yields a more accurate isotropic 3D representation of the examined object than original DTS reconstructions. By utilizing a dual-view DTS acquisition geometry some advantages of including DTS data from orthogonal projection angles were illustrated. The findings are encouraging for further work on reconstruction algorithms using a dual-view DTS acquisition geometry.
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| 10. |
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| 11. |
- Ásgeirsdóttir, Helga, et al.
(författare)
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Depiction of anatomic structures of relevance for scoring of cystic fibrosis changes by chest tomosynthesis and computed tomography
- 2014
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Ingår i: Journal of Cystic Fibrosis. 37th European Cystic Fibrosis Conference, 11-14 June 2014, Gothenburg, Sweden. ; 13:Suppl. 2
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Introduction: Chest radiography (CR) and computed tomography (CT) are commonly used for imaging of patients with cystic fibrosis, and scoring is applied to assess disease severity. Chest tomosynthesis (CTS) is a new imaging modality providing better anatomic visualization than CR at radiation doses and costs lower than CT. Objective: To compare visibility and size of anatomic structures of relevance for scoring in CTS and CT images. Methods: 21 adult patients with cystic fibrosis were examined both with CTS (VolumeRAD; GE Healthcare) and volumetric CT (LightSpeed Pro 16, LightSpeed VCT, Discovery CT750HD; GE healthcare and Somatom Definition, Siemens Medical Solutions). The average effective dose for a standard patient was 0.13 and 4.5 mSv for CTS and CT, respectively. Comparison of visibility and manual measurements of diameters of the central and peripheral bronchi and their accompanying artery, as well as bronchial wall thickness (BWT), were performed in a non-blinded fashion. Results: All central structures could be evaluated. Mean difference in diameter of central bronchi, accompanying artery and BWT between CTS and CT was −0.6 (SD 0.6), −0.7 (SD 0.7) and −0.4 (SD 0.2) mm, respectively. Peripheral structures were more difficult to assess by CTS. Peripheral bronchial diameter, BWT and diameter of accompanying artery could be assessed by CTS in 20, 15 and 4 cases, respectively and mean difference between measurements was −0.5 (SD 0.5), −0.3 (SD 0.3) and −0.4 (SD 0.4) mm, respectively. Conclusion: This study indicates that peripheral structures are more difficult to evaluate by CTS and that CTS slightly underestimate size of structures in comparison to CT
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| 12. |
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| 13. |
- Asplund, Sara, 1976, et al.
(författare)
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Extended analysis of the effect of learning with feedback on the detectability of pulmonary nodules in chest tomosynthesis
- 2011
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 7966
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In chest tomosynthesis, low-dose projections collected over a limited angular range are used for reconstruction of section images of the chest, resulting in a reduction of disturbing anatomy at a moderate increase in radiation dose compared to chest radiography. In a previous study, we investigated the effects of learning with feedback on the detection of pulmonary nodules in chest tomosynthesis. Six observers with varying degrees of experience of chest tomosynthesis analyzed tomosynthesis cases for presence of pulmonary nodules. The cases were analyzed before and after learning with feedback. Multidetector computed tomography (MDCT) was used as reference. The differences in performance between the two readings were calculated using the jackknife alternative free-response receiver operating characteristics (JAFROC-2) as primary measure of detectability. Significant differences between the readings were found only for observers inexperienced in chest tomosynthesis. The purpose of the present study was to extend the statistical analysis of the results of the previous study, including JAFROC-1 analysis and FROC curves in the analysis. The results are consistent with the results of the previous study and, furthermore, JAFROC-1 gave lower p-values than JAFROC-2 for the observers who improved their performance after learning with feedback. © 2011 SPIE.
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| 14. |
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| 15. |
- Asplund, Sara, 1976, et al.
(författare)
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Learning aspects and potential pitfalls regarding detection of pulmonary nodules in chest tomosynthesis and proposed related quality criteria.
- 2011
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Ingår i: Acta radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 52:5, s. 503-512
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Tidskriftsartikel (refereegranskat)abstract
- Background 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. Purpose 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. Material and Methods 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. Results 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. Conclusion 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.
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| 16. |
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| 17. |
- Berner, Karin, et al.
(författare)
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Dose optimisation of double-contrast barium enema examinations.
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 388-392
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present work was to optimise the filtration and dose setting for double-contrast barium enema examinations using a Philips MultiDiagnost Eleva FD system. A phantom study was performed prior to a patient study. A CDRAD phantom was used in a study where copper and aluminium filtration, different detector doses and tube potentials were examined. The image quality was evaluated using the software CDRAD Analyser and the phantom dose was determined using the Monte Carlo-based software PCXMC. The original setting [100 % detector dose (660 nGy air kerma) and a total filtration of 3.5 mm Al, at 81 kVp] and two other settings identified by the phantom study (100 % detector dose and additional filtration of 1 mm Al and 0.2 mm Cu as well as 80 % detector dose and added filtration of 1 mm Al and 0.2 mm Cu) were included in the patient study. The patient study included 60 patients and up to 8 images from each patient. Six radiologists performed a visual grading characteristics study to evaluate the image quality. A four-step scale was used to judge the fulfillment of three image quality criteria. No overall statistical significant difference in image quality was found between the three settings (P > 0.05). The decrease in the effective dose for the settings in the patient study was 15 % when filtration was added and 34 % when both filtrations was added and detector dose was reduced. The study indicates that additional filtration of 1 mm Al and 0.2 mm Cu and a decrease in detector dose by 20 % from the original setting can be used in colon examinations with Philips MultiDiagnost Eleva FD to reduce the patient dose by 30 % without significantly affecting the image quality. For 20 exposures, this corresponds to a decrease in the effective dose from 1.6 to 1.1 mSv.
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| 18. |
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Båth, Magnus, 1974, et al.
(författare)
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A conceptual optimisation strategy for radiography in a digital environment.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 230-5
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Tidskriftsartikel (refereegranskat)abstract
- Using a completely digital environment for the entire imaging process leads to new possibilities for optimisation of radiography since many restrictions of screen/film systems, such as the small dynamic range and the lack of possibilities for image processing, do not apply any longer. However, at the same time these new possibilities lead to a more complicated optimisation process, since more freedom is given to alter parameters. This paper focuses on describing an optimisation strategy that concentrates on taking advantage of the conceptual differences between digital systems and screen/film systems. The strategy can be summarised as: (a) always include the anatomical background during the optimisation, (b) perform all comparisons at a constant effective dose and (c) separate the image display stage from the image collection stage. A three-step process is proposed where the optimal setting of the technique parameters is determined at first, followed by an optimisation of the image processing. In the final step the optimal dose level-given the optimal settings of the image collection and image display stages-is determined.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Båth, Magnus, 1974, et al.
(författare)
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Chest tomosynthesis
- 2014
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Ingår i: Tomosynthesis Imaging. Ed. Stephen Glick. - Boca Raton : CRC Press/Taylor & Francis. - 9781439878705 ; , s. 189-197
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 27. |
- Båth, Magnus, 1974, et al.
(författare)
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Determination of the two-dimensional detective quantum efficiency of a computed radiography system.
- 2003
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 30:12, s. 3172-82
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Tidskriftsartikel (refereegranskat)abstract
- Based on a recently described method for determining the two-dimensional presampling modulation transfer function (MTF), the aperture mask method, a method for determining the two-dimensional detective quantum efficiency (DQE) of a digital radiographic system was developed. The method was applied to a new computed radiography (CR) system and comparisons with one-dimensional determinations of the presampling MTF and the DQE were performed. The aperture mask method was shown to agree with the conventional tilted slit method for determining the presampling MTF along the axes. For the particular CR system studied, the mean of one-dimensional determinations of the DQE in orthogonal directions led to a representative measure of the average DQE behavior of the system up to the Nyquist frequency along the axes, but a deviation was observed above this frequency. In conclusion, the method developed for determining the two-dimensional DQE can be used to determine the imaging properties of a digital radiographic detector system over almost the entire frequency domain, the exception being the lowest frequencies (< or = 0.1 mm(-1)) at which the validity and the reliability of the method are low.
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| 28. |
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| 29. |
- Båth, Magnus, 1974
(författare)
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DQE: Hur är läget?
- 2004
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Ingår i: Röntgenveckan 2004, Göteborg, 6-10 september 2004.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 30. |
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| 31. |
- Båth, Magnus, 1974, et al.
(författare)
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Effective dose to patients from chest examinations with tomosynthesis
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 153-158
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Tidskriftsartikel (refereegranskat)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.
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| 32. |
- Båth, Magnus, 1974
(författare)
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Evaluating imaging systems: practical applications
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 26-36
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Tidskriftsartikel (refereegranskat)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.
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| 33. |
- Båth, Magnus, 1974
(författare)
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Evaluating imaging systems – practical applications
- 2009
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Ingår i: Third Malmö Conference on Medical Imaging: Optimisation in X-Ray and Molecular Imaging, Malmö, Sweden, 25-27 June 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 34. |
- Båth, Magnus, 1974, et al.
(författare)
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Evaluation of the imaging properties of two generations of a CCD-based system for digital chest radiography.
- 2002
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 29:10, s. 2286-97
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Tidskriftsartikel (refereegranskat)abstract
- Two generations of a CCD-based detector system with lens-based optical coupling for digital chest radiography were evaluated in terms of presampling MTF, NPS, NEQ, DQE, linearity in response, and SNR over the detector area. Measurements were performed over a wide exposure range and at several different beam qualities. Neither the presampling MTF nor the DQE showed any general strong beam quality dependence, whereas the NPS and NEQ did when compared at specific entrance air kerma values. The exposure dependency for the DQE was found to be considerable, with the detectors showing low DQE at low exposures, and higher DQE at higher exposures. It was found that the second generation has been substantially improved compared to its predecessor regarding all the relevant parameters. The DQE(0) at an entrance air kerma of 5 microGy increased from 9% to 15%, mainly due to a better system gain (including optical coupling efficiency and matching of the energy of the emitted light photons to the sensitivity of the CCD camera). The first generation of detectors was found to have problems with bad peripheral resolution [MTF(muN/2) <0.1]. This problem was nonexistent for the second generation for which uniform resolution has been obtained [MTF(muN/2)=0.3]. A theoretical calculation of the DQE of two model systems similar to the ones evaluated was also performed, and the results were comparable to the experimentally determined data at high exposures. The model shows that both systems suffer from low optical coupling efficiency due to the large demagnification used. The main conclusion is that although the second generation has been improved, there is still a problem with low system gain leading to relatively modest DQE values, especially at low exposures.
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| 35. |
- Båth, Magnus, 1974, et al.
(författare)
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Investigation of image components affecting the detection of lung nodules in digital chest radiography
- 2005
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 5749, s. 231-242
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work was to investigate and quantify the effects of system noise, nodule location, anatomical noise and anatomical background on the detection of lung nodules in different regions of the chest x-ray. Simulated lung nodules of diameter 10 mm but with varying detail contrast were randomly positioned in four different kinds of images: 1) clinical images collected with a 200 speed CR system, 2) images containing only system noise (including quantum noise) at the same level as the clinical images, 3) clinical images with removed anatomical noise, 4) artificial images with similar power spectrum as the clinical images but random phase spectrum. An ROC study was conducted with 5 observers. The detail contrast needed to obtain an Az of 0.80, C0.8, was used as measure of detectability. Five different regions of the chest x-ray were investigated separately. The C0.8 of the system noise images ranged from only 2% (the hilar regions) to 20% (the lateral pulmonary regions) of those of the clinical images. Compared with the original clinical images, the C0.8 was 16% lower for the de-noised clinical images and 71% higher for the random phase images, respectively, averaged over all five regions. In conclusion, regarding the detection of lung nodules with a diameter of 10 mm, the system noise is of minor importance at clinically relevant dose levels. The removal of anatomical noise and other noise sources uncorrelated from image to image leads to somewhat better detection, but the major component disturbing the detection is the overlapping of recognizable structures, which are, however, the main aspect of an x-ray image.
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| 36. |
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| 37. |
- Båth, Magnus, 1974, et al.
(författare)
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Investigation of parameters concerning the modulation transfer function in digital radiography
- 2001
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X. ; 4320, s. 350-361
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The effects of the design of a radiographic system on the modulation transfer function (MTF) are studied with a specially developed computer program. The program simulates a digital radiographic system by using three parameters: sampling distance, sampling aperture, and the spread of the signal in the detector due to the interaction processes of the incoming photons. The signal spread is approximated by Gaussian distributions. The influence of the three parameters is studied on the presampling MTF and on the two extreme cases of the digital MTF: The maximum MTF and the minimum MTF. From theoretical data on the interaction processes, the resolution properties of an amorphous selenium flat-panel detector are simulated. The program is also used to simulate a measurement of the presampling MTF with the slit method, and the effect of the slit width on the measured presampling MTF is examined.
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| 38. |
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| 39. |
- Båth, Magnus, 1974, et al.
(författare)
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Method for determining the two-dimensional presampling modulation transfer function in digital radiography
- 2001
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X. ; 4320, s. 268-279
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In digital radiography, radial asymmetry may be present. The use of a one-dimensional representation of the resolution properties can therefore be questioned. Although measurements are often done in two orthogonal directions, there may be a need for a more detailed description. A method of measuring the two-dimensional presampling modulation transfer function (MTF) has therefore been developed. A finely sampled "disk spread function" is obtained by imaging an aperture mask, consisting of N2 circular holes arranged in an N×N manner in an opaque material, in such a way that each hole is positioned at a different phase relative to the sampling coordinates of the detector system. This spread function is resampled, extrapolated, Fourier transformed, and finally corrected for the finite hole size in order to obtain the presampling MTF. The method was tested on a computed radiography (CR) system through measurements with a prototype mask, consisting of 100 holes of radius 0.2 mm drilled in a lead alloy. The results were compared with measurements using the slit method, and were found to be consistent. Problems associated with the method, e.g. errors due to incorrect alignment of the holes in the aperture mask with the beam, and limitations due to the finite hole size, are discussed.
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| 40. |
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| 41. |
- Båth, Magnus, 1974, et al.
(författare)
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Method of simulating dose reduction for digital radiographic systems.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 253-9
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Tidskriftsartikel (refereegranskat)abstract
- The optimisation of image quality vs. radiation dose is an important task in medical imaging. To obtain maximum validity of the optimisation, it must be based on clinical images. Images at different dose levels can then either be obtained by collecting patient images at the different dose levels sought to investigate-including additional exposures and permission from an ethical committee-or by manipulating images to simulate different dose levels. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems. The method uses information about the detective quantum efficiency and noise power spectrum at the original and simulated dose levels to create an image containing filtered noise. When added to the original image this results in an image with noise which, in terms of frequency content, agrees with the noise present in an image collected at the simulated dose level. To increase the validity, the method takes local dose variations in the original image into account. The method was tested on a computed radiography system and was shown to produce images with noise behaviour similar to that of images actually collected at the simulated dose levels. The method can, therefore, be used to modify an image collected at one dose level so that it simulates an image of the same object collected at any lower dose level.
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| 42. |
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| 43. |
- Båth, Magnus, 1974
(författare)
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Neonatalundersökningar i digital miljö
- 2003
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Ingår i: Röntgenveckan 2003, Norrköping, 15-19 September 2003.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 44. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: effect of anatomical noise.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 109-13
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Tidskriftsartikel (refereegranskat)abstract
- The image background resulting from imaged anatomy can be divided into those components that are meaningful to the observers, in the sense that they are recognised as separate structures, and those that are not. These latter components (reffered to as anatomical noise) can be removed using a method developed within the RADIUS group. The aim of the present study was to investigate whether the removal of the anatomical noise results in images where lung nodules with lower contrast can be detected. A receiver operating characteristic (ROC) study was therefore conducted using two types of images: clinical chest images and chest images in which the anatomical noise had been removed. Simulated designer nodules with a full-width-at-fifth-maximum of 10 mm but with varying contrast were added to the images. The contrast needed to obtain an area under the ROC curve of 0.80, C0.8, was used as a measure of detectability (a low value of C0.8 represents a high detectability). Five regions of the chest X ray were investigated and it was found that in all regions the removal of anatomical noise led to images with lower C0.8 than the original images. On average, C0.8 was 20% higher in the original images, ranging from 7% (the lateral pulmonary regions) to 41% (the upper mediastinal regions).
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| 45. |
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| 46. |
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| 47. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: introduction to the RADIUS chest trial.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 85-91
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Tidskriftsartikel (refereegranskat)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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| 48. |
- Båth, Magnus, 1974, et al.
(författare)
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Nodule detection in digital chest radiography: part of image background acting as pure noise.
- 2005
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 102-8
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Tidskriftsartikel (refereegranskat)abstract
- There are several factors that influence the radiologist's ability to detect a specific structure/lesion in a radiograph. Three factors that are commonly known to be of major importance are the signal itself, the system noise and the projected anatomy. The aim of this study was to determine to what extent the image background acts as pure noise for the detection of subtle lung nodules in five different regions of the chest. A receiver operating characteristic (ROC) study with five observers was conducted on two different sets of images, clinical chest X-ray images and images with a similar power spectrum as the clinical images but with a random phase spectrum, resulting in an image background containing pure noise. Simulated designer nodules with a full-width-at-fifth-maximum of 10 mm but with varying contrasts were added to the images. As a measure of the part of the image background that acts as pure noise, the ratio between the contrast needed to obtain an area under the ROC curve of 0.80 in the clinical images to that in the random-phase images was used. The ratio ranged from 0.40 (in the lateral pulmonary regions) to 0.83 (in the hilar regions) indicating that there was a large difference between different regions regarding to what extent the image background acted as pure noise; and that in the hilar regions the image background almost completely acted as pure noise for the detection of 10 mm nodules.
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| 49. |
- Båth, Magnus, et al.
(författare)
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OPTIMISATION in X-RAY and MOLECULAR IMAGING 2020
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 195:3-4, s. 133-133
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 50. |
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