VIEWDEX: an efficient and easy-to-use software for observer performance studies.

The development of investigation techniques, image processing, workstation monitors, analysing tools etc. within the field of radiology is vast, and the need for efficient tools in the evaluation and optimisation process of image and investigation quality is important. ViewDEX (Viewer for Digital Evaluation of X-ray images) is an image viewer and task manager suitable for research and optimisation tasks in medical imaging. ViewDEX is DICOM compatible and the features of the interface (tasks, image handling and functionality) are general and flexible. The configuration of a study and output (for example, answers given) can be edited in any text editor. ViewDEX is developed in Java and can run from any disc area connected to a computer. It is free to use for non-commercial purposes and can be downloaded from http://www.vgregion.se/sas/viewdex. In the present work, an evaluation of the efficiency of ViewDEX for receiver operating characteristic (ROC) studies, free-response ROC (FROC) studies and visual grading (VG) studies was conducted. For VG studies, the total scoring rate was dependent on the number of criteria per case. A scoring rate of approximately 150 cases h(-1) can be expected for a typical VG study using single images and five anatomical criteria. For ROC and FROC studies using clinical images, the scoring rate was approximately 100 cases h(-1) using single images and approximately 25 cases h(-1) using image stacks ( approximately 50 images case(-1)). In conclusion, ViewDEX is an efficient and easy-to-use software for observer performance studies.

Optimisation of tube voltage for conventional urography using a Gd2O2S:Tb flat panel detector.

With the increasing use of computed tomography (CT) for urography examinations, the indications for 'conventional' projection urography have changed and are more focused on high-contrast details. The purpose of the present study was to optimise the beam quality for urography examinations performed with a Gd(2)O(2)S:Tb flat-panel detector for the new conditions. Images of an anthropomorphic phantom were collected at different tube voltages with a CXDI-40G detector (Canon Inc., Tokyo, Japan). The images were analysed by radiologists and residents in a visual grading characteristics (VGCs) study. The tube voltage resulting in the best image quality was 55 kV, which therefore was selected for a clinical study. Images from 62 patients exposed with either 55 or 73 kV (original tube voltage) at constant effective doses were included. The 55-kV images underwent simulated dose reduction to represent images collected at 80, 64, 50, 40 and 32 % of the original dose level. All images were included in a VGC study where the observers rated the visibility of important anatomical landmarks. For images collected at 55 kV, an effective dose of approximately 85 % resulted in the same image quality as for images collected at 73 kV at 100 % dose. In conclusion, a low tube voltage should be used for conventional urography focused on high-contrast details. The study indicates that using a tube voltage of 55 kV instead of 73 kV for a Gd(2)O(2)S:Tb flat-panel detector, the effective dose can be reduced by approximately 10-20 % for normal-sized patients while maintaining image quality.

Comparison of chest tomosynthesis and chest radiography for detection of pulmonary nodules: human observer study of clinical cases.

PURPOSE: To compare chest tomosynthesis with chest radiography in the detection of pulmonary nodules by using multidetector computed tomography (CT) as the reference method. MATERIALS AND METHODS: The Regional Ethical Review Board approved this study, and all participants gave informed consent. Four thoracic radiologists acted as observers in a jackknife free-response receiver operating characteristic (JAFROC) study conducted in 42 patients with and 47 patients without pulmonary nodules examined with chest tomosynthesis and chest radiography. Multidetector CT served as reference method. The observers marked suspected nodules on the images by using a four-point rating scale for the confidence of presence. The JAFROC figure of merit was used as the measure of detectability. The number of lesion localizations relative to the total number of lesions (lesion localization fraction [LLF]) and the number of nonlesion localizations relative to the total number of cases (nonlesion localization fraction [NLF]) were determined. RESULTS: Performance of chest tomosynthesis was significantly better than that of chest radiography with regard to detectability (F statistic = 32.7, df = 1, 34.8, P < .0001). For tomosynthesis, the LLF for the smallest nodules (< or = 4 mm) was 0.39 and increased with an increase in size to an LLF for the largest nodules (> 8 mm) of 0.83. The LLF for radiography was small, except for the largest nodules, for which it was 0.52. In total, the LLF was three times higher for tomosynthesis. The NLF was approximately 50% higher for tomosynthesis. CONCLUSION: For the detection of pulmonary nodules, the performance of chest tomosynthesis is better, with increased sensitivity especially for nodules smaller than 9 mm, than that of chest radiography.