| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Båth, Magnus, 1974, et al.
(författare)
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VGC analysis: Application of the ROC methodology to visual grading tasks
- 2008
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6917
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To determine clinical image quality in radiography, visual grading of the reproduction of important anatomical landmarks is often used. The rating data from the observers in a visual grading study with multiple scale steps is ordinal, meaning that non-parametric rank-invariant statistical methods are required. However, many visual grading methods incorrectly use parametric statistical methods. This work describes how the methodology developed in receiver operating characteristics (ROC) analysis for characterising the difference in the observer's response to the signal and no-signal distributions can be applied to visual grading data for characterising the difference in perceived image quality between two systems. The method is termed visual grading characteristics (VGC) analysis. In a VGC study, the task of the observer is to rate her confidence about the fulfilment of image quality criteria. Using ROC software, the given ratings for the two systems are then used to determine the VGC curve, which describes the relationship between the proportions of fulfilled image criteria for the two compared systems for all possible decision thresholds. As a single measure of the difference in image quality between the two compared systems, the area under the VGC curve can be used.
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| 6. |
- Håkansson, Markus, et al.
(författare)
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ViewDEX 2.0: A Java-based DICOM-compatible software for observer performance studies
- 2009
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 7263
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- ViewDEX (Viewer for Digital Evaluation of X-ray images) is a Java-based DICOM-compatible software tool for observer performance studies that can be used to display medical images with simultaneous registration of the observer's response. The current release, ViewDEX 2.0, is a development of ViewDEX 1.0, which was released in 2007. Both versions are designed to run in a Java environment and do not require any special installation. For example, the program can be located on a memory stick or stand alone hard drive and be run from there. ViewDEX is managed and configured by editing property files, which are plain text files where users, tasks (questions, definitions, etc.) and functionality (WW/WL, PAN, ZOOM, etc.) are defined. ViewDEX reads most common DICOM image formats and the images can be stored in any location connected to the computer. ViewDEX 2.0 is designed so that the user in a simple way can alter if the questions presented to the observers are related to localization or not, enabling e.g. free-response ROC, standard ROC and visual grading studies, as well as combinations of these, to be conducted in a fast and efficient way. The software can also be used for bench marking and for educational purposes. The results from each observer are saved in a log file, which can be exported for further analysis. The software is freely available for non-commercial purposes.
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| 7. |
- Håkansson, Markus, et al.
(författare)
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ViewDEX - A Java-based software for presentation and evaluation of medical images in observer performance studies
- 2007
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6509
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Observer performance studies are time-consuming tasks, both for the participating observers and for the scientists collecting and analyzing the data. A possible way to optimize such studies is to perform the study 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 a DICOM-compatible software tool that can be used to display medical images with simultaneous registration of the observer's response. ViewDEX is designed so that the user in a simple way can alter the types of questions and images presented to the observers, enabling ROC, MAFC and visual grading studies to be conducted in a fast and efficient way. The software can also be used for bench marking and for educational purposes. The results from each observer are saved in a log file, which can be exported for further analysis. The software is freely available for non-commercial purposes.
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| 8. |
- Mattsson, Sören, et al.
(författare)
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Special issue: Medical imaging--optimisation in X-ray and molecular imaging.
- 2010
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Ingår i: Radiation protection dosimetry. - : Oxford University Press (OUP). - 1742-3406 .- 0144-8420. ; 139:1-3, s. 1-2
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This issue of Radiation Protection Dosimetry is based on contributions to the Third Malmö Conference on Medical Imaging, which was held from 25 to 27 June 2009 at the Malmö University Hospital, Sweden. The conference was jointly organised by members of current and former research projects supported by the European Commission EURATOM-Radiation Protection Research Programme.
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| 9. |
- Ruschin, Mark, et al.
(författare)
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Improved in-plane visibility of tumors using breast tomosynthesis
- 2007
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422 .- 1042-4687. ; 6510
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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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| 10. |
- Sund, Patrik, et al.
(författare)
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A comparison between 8-bit and 10-bit luminance resolution when generating low-contrast sinusoidal test pattern on an LCD
- 2007
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Ingår i: Progress in Biomedical Optics and Imaging - Proceedings of SPIE. - : SPIE. - 1605-7422. ; 6515
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Radiological images are today mostly displayed on monitors, but much is still unknown regarding the interaction between monitor and viewer. Issues like monitor luminance range, calibration, contrast resolution and luminance distribution need to be addressed further. To perform vision research of high validity to the radiologists, test images should be presented on medical displays. One of the problems has been how to display low contrast patterns in a strictly controlled way. This paper demonstrates how to generate test patterns close to the detection limit on a medical grade display using subpixel modulation. Patterns are generated with both 8-bit and 10-bit monitor input. With this technique, up to 7162 luminance levels can be displayed and the average separation is approximately 0.08 of a JND (Just Noticeable Difference) on a display with a luminance range between 1 and 400 cd/m2. These patterns were used in a 2AFC detection task and the detection threshold was found to be 0.75 ± 0.02 of a JND when the adaptation level was the same as the target luminance (20 cd/m2). This is a reasonable result considering that the magnitude of a JND is based on the method of adjustment rather than on a detection task. When test patterns with a different luminance than the adaptation level (20 cd/m2) were displayed, the detection thresholds were 1.11 and 1.06 of a JND for target luminance values 1.8 and 350 cd/m2, respectively.
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