| 111. |
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| 112. |
- Svalkvist, Angelica, et al.
(författare)
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Evaluation of an improved method of simulating lung nodules in chest tomosynthesis
- 2012
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 53:8, s. 874-884
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Tidskriftsartikel (refereegranskat)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.
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| 113. |
- Svalkvist, Angelica, et al.
(författare)
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Investigation of the dosimetry of chest tomosynthesis
- 2009
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 7258
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Chest tomosynthesis has recently been introduced to healthcare as a low-dose alternative to CT or as a tool for improved diagnostics in chest radiography with only a modest increase in radiation dose to the patient. However, no detailed description of the dosimetry for this type of examination has been presented. The aim of this work was therefore to investigate the dosimetry of chest tomosynthesis. The chest tomosynthesis examination was assumed to be performed using a stationary detector and a vertically moving x-ray tube, exposing the patient from different angles. The Monte Carlo-based computer software PCXMC was used to determine the effective dose delivered to a standard-sized patient from various angles using different assumptions of the distribution of the effective dose over the different projections. The obtained relationships between input dose measures and effective dose for chest tomosynthesis for different angular intervals were then compared with the osteroanterior (PA) projection. The results indicate that the error is small when using the assumption that all effective dose in the case of chest tomosynthesis is delivered in PA projection for estimating the total effective dose for chest tomosynthesis for normally sized patients. This is especially true if the relationship between the kerma-area product (KAP) and effective dose is used. © 2009 SPIE.
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| 114. |
- Svalkvist, Angelica, et al.
(författare)
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Monte Carlo simulations of the dosimetry of chest tomosynthesis
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 144-152
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Tidskriftsartikel (refereegranskat)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.
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| 115. |
- Svalkvist, Angelica, et al.
(författare)
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Simulation of dose reduction in tomosynthesis.
- 2010
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Ingår i: Medical physics. - : Wiley. - 0094-2405. ; 37:1, s. 258-69
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.
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| 116. |
- Svalkvist, Angelica, et al.
(författare)
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Simulation of lung nodules in chest tomosynthesis
- 2010
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Ingår i: RADIATION PROTECTION DOSIMETRY. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 139:1-3, s. 130-139
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present work was to develop an adequate method for simulating lung nodules in clinical chest tomosynthesis images. Based on the visual appearance of real nodules, artificial, three-dimensional nodules with irregular shape and surface structure were created using an approach of combining spheres of different sizes and central points. The nodules were virtually positioned at the desired locations inside the patient and by using the known geometry of the tomosynthesis acquisition, the radiation emitted from the focal spot, passing through the nodule and reaching the detector could be simulated. The created nodules were thereby projected into raw-data tomosynthesis projection images before reconstruction of the tomosynthesis section images. The focal spot size, signal spread in the detector, scattered radiation, patient motion and existing anatomy at the location of the nodule were taken into account in the simulations. It was found that the blurring caused by the modulation transfer function and the patient motion overshadows the effects of a finite focal spot and aliasing and also obscures the surface structure of the nodules, which provides an opportunity to simplify the simulations and decrease the simulation times. Also, the limited in-depth resolution of the reconstructed tomosynthesis section images reduces the necessity to take details of the anatomical structures at the location of the inserted nodule into account.
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| 117. |
- Svalkvist, Angelica, et al.
(författare)
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The benefit of accounting for DQE variations in simulated dose reduction of digital radiographic systems
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 57-61
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Tidskriftsartikel (refereegranskat)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.
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| 118. |
- Svalkvist, Angelica, et al.
(författare)
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VIEWDEX 3.0-RECENT DEVELOPMENT OF A SOFTWARE APPLICATION FACILITATING ASSESSMENT OF IMAGE QUALITY AND OBSERVER PERFORMANCE
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 195:3-4, s. 372-377
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Tidskriftsartikel (refereegranskat)abstract
- ViewDEX (Viewer for Digital Evaluation of X-ray Images) is an image viewer compatible with Digital Imaging and Communications in Medicine (DICOM) that has been especially designed to facilitate image perception and observer performance studies within medical imaging. The software was first released in 2004 and since then a continuous development has been ongoing. One of the major drawbacks of previous versions of ViewDEX has been that they have lacked functionality enabling the possibility to evaluate multiple images and/or image stacks simultaneously. This functionality is especially requested by researchers working with modalities, where an image acquisition can result in multiple image stacks (e.g. axial, coronal and sagittal reformations in computed tomography). In ViewDEX 3.0 this functionality has been added and it is now possible to perform image evaluations of multiple images and/or image stacks simultaneously, by using multiple monitors and/or multiple image canvases in monitors. Additionally, some of the previously available functionality has been updated and improved. This paper describes the recent developments of ViewDEX 3.0.
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| 119. |
- Svalkvist, Angelica, et al.
(författare)
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VIEWDEX: A STATUS REPORT
- 2016
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 169:1-4, s. 38-45
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Tidskriftsartikel (refereegranskat)abstract
- 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. The software has undergone continuous development during more than a decade and has during this time period been used in numerous studies. ViewDEX is DICOM compatible, and the features of the interface (tasks, image handling and functionality) are general and flexible. The set-up of a study is determined by altering properties in a text-editable file, enabling easy and flexible configuration. 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. The purposes of the present article are to give a short overview of the development of ViewDEX and to describe recent updates of the software. In addition, a description on how to configure a viewing session in ViewDEX is provided.
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| 120. |
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