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ARTICLE

American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase III

Measurement of image quality differences at varying levels of data compression

R.üdiger Brennecke, PhD^*, Udo Bürgel, MS^*, R.üdiger Simon, MD, FACC, Gerd Rippin, MS, Hans Peter Fritsch, MS^*, Tim Becker, MS and Steven E. Nissen, MD, FACC

^* II Medical Clinic, Johannes-Gutenberg-University Mainz, Germany
Medical Clinic, Albrechts-University Kiel, Germany
Department of Medical Statistics, Johannes-Gutenberg-University Mainz, Germany
Cleveland Clinic Foundation, Cleveland, Ohio, USA

Manuscript received June 1, 1999; accepted December 1, 1999.

Reprint requests and correspondence: Dr. Rüdiger Brennecke, II Medical Clinic, Johannes-Gutenberg-University Hospital, D55131 Mainz, Germany
incis.rb{at}uni-mainz.de

OBJECTIVES

We sought to investigate up to which level of Joint Photographic Experts Group (JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms.

BACKGROUND

Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive.

METHODS

Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differences were assessed on a scale featuring six scores. In addition, the raters had to detect pre-defined clinical features. Compression ratios (CR) were 6:1, 10:1 and 16:1. Statistical evaluation was based on descriptive statistics and on the equivalence t-test.

RESULTS

At the lowest CR (CR 6:1), there was already a small (15%) increase in assigning the aesthetic quality score indicating "quality difference is barely discernible—the images are equivalent." At CR 10:1 and CR 16:1, close to 10% and 55%, respectively, of the compressed images were rated to be "clearly degraded, but still adequate for clinical use" or worse. Concerning diagnostic features, at CR 10:1 and CR 16:1 the error rate was 9.6% and 13.1%, respectively, compared with 9% for the baseline error rate in uncompressed images.

CONCLUSIONS

Compression at CR 6:1 provides equivalence with the original cine runs. If CR 16:1 were used, one would have to tolerate a significant increase in the diagnostic error rate over the baseline error rate. At CR 10:1, intermediate results were obtained.

Abbreviations and Acronyms   ACC = American College of Cardiology   CR = compression ratio   DC = display controls   ESC = European Society of Cardiology   fps = frames per second   GQ = general image quality   JPEG = Joint Photographic Experts Group (computer standard for digital images)   QA = aesthetic image quality   QCA = quantitative coronary angiography   QD = diagnostic image quality   ROI = region of interest   SD = standard deviation

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