Pan-Canadian evaluation of irreversible compression ratios ("lossy" compression) for development of national guidelines.

New technological advancements including multislice CT scanners and functional MRI, have dramatically increased the size and number of digital images generated by medical imaging departments. Despite the fact that the cost of storage is dropping, the savings are largely surpassed by the increasing volume of data being generated. While local area network bandwidth within a hospital is adequate for timely access to imaging data, efficiently moving the data between institutions requires wide area network bandwidth, which has a limited availability at a national level. A solution to address those issues is the use of lossy compression as long as there is no loss of relevant information. The goal of this study was to determine levels at which lossy compression can be confidently used in diagnostic imaging applications. In order to provide a fair assessment of existing compression tools, we tested and compared the two most commonly adopted DISCOM compression algorithms: JPEG and JPEG-2000. We conducted an extensive pan-Canadian evaluation of lossy compression applied to seven anatomical areas and five modalities using two recognized techniques: objective methods or diagnostic accuracy and subjective assessment based on Just Noticeable Difference. By incorporating both diagnostic accuracy and subjective evaluation techniques, enabled us to define a range of compression for each modality and body part tested. The results of our study suggest that at low levels of compression, there was no significant difference between the performance of lossy JPEG and lossy JPEG 2000, and that they are both appropriate to use for reporting on medical images. At higher levels, lossy JPEG proved to be more effective than JPEG 2000 in some cases, mainly neuro CT. More evaluation is required to assess the effect of compression on thin slice CT. We provide a table of recommended compression ratios for each modality and anatomical area investigated, to be integrated in the Canadian Association of Radiologists standard for the use of lossy compression in medical imaging.

An overview of digital compression of medical images: can we use lossy image compression in radiology?

The increasing volume of data generated by new imaging modalities such as multislice computed tomography scanners and magnetic resonance imaging justifies the use of lossy compression techniques to decrease the cost of storage and improve the efficiency of transmission over networks for teleradiology or for access to electronic patient records. We summarize here the most commonly used compression techniques and compare their main features. Having conducted an extensive literature review, we present a range of average compression ratios for different modalities and body parts. This article lays the groundwork for further evaluation with standardized statistical methods to ultimately elaborate acceptable compression guidelines.

Severe acute respiratory syndrome: radiographic review of 40 probable cases in Toronto, Canada.

PURPOSE: To review radiographic findings of patients with probable severe acute respiratory syndrome (SARS) who were seen at a University of Toronto (Ontario, Canada) teaching hospital. MATERIALS AND METHODS: Findings were reviewed for 40 patients who fulfilled the World Health Organization criteria for probable SARS. A template was designed for the analysis of each serial radiograph to observe patterns and distribution of disease, interval changes, and complications. The majority of radiographs were anteroposterior views. A clinical database of these patients was also collected for clinical-radiologic comparison. RESULTS: The mean age of the patients (18 male, 22 female) was 42.7 years. Patients had a normal chest radiograph and focal, multifocal, and/or bilateral consolidation. The pattern of consolidation tended to be peripheral and poorly marginated and involved middle and lower lung zones. The serial sequence fell into two major subgroups, which correlated closely with clinical outcome. Consolidation in one group cleared within a matter of days, while the second group went on to develop rapid and extensive bilateral pneumonia, with a prolonged hospital stay. Subsegmental atelectasis and pleural complications were rarely observed. CONCLUSION: SARS pneumonia can manifest as focal peripheral consolidation that clears relatively quickly and does not cause secondary complications or that progresses to bilateral consolidation and a more protracted clinical course.