EFFECT OF LOSSY DATA-COMPRESSION ON QUANTITATIVE CORONARY MEASUREMENTS

With the accepted use of (lossy) data compression at low compression f actors (2, 3 and 4 on the Philips DCI), the question was posed whether higher lossy compression ratios can also be used without statisticall y affecting the results of quantitative coronary arteriography. In thi s study the influence of two data compression schemes (LOT and JPEG) a t three different compression factors (5, 8 and 12) on coronary measur ements was assessed with the Automated Coronary Analysis (ACA) package . A series of 30 original acquired digital images were compressed and decompressed at the different factors, and together with the original non-compressed images processed using the ACA package. In these images a total of 37 obstructed coronary segments were analyzed twice to ass ess the intraobserver variabilities in the obstruction and reference d iameters and in the percent diameter stenosis. The results of the firs t and second measurements in each image were averaged, and from the di fferences in corresponding images with different compression ratios, t he inter-compression variability was obtained. The results show that t he intraobserver systematic errors in the absolute diameters are all s mall (< 0.07 mm), and statistically not significantly different. The i ntra-observer random errors for the compressed/decompressed series, ho wever, were all larger (up to 0.21 mm) than for the original series(< 0.13 mm). Statistically significant differences in the intra-observer random errors were found for the JPEG compression scheme at a compress ion ratio of 5 and for the LOT scheme at a compression ratio of 12. Th e inter-compression systematic errors in the absolute diameter measure ments were also small (< 0.07 mm) and not significant, while the rando m errors were found to be high in the range between 0.23 mm and 0.31 m m. Given the higher intra-observer variabilities for the compressed/de compressed image series as compared to original images, and the fact t hat all inter-compression variabilities were found to be so high, we m ust conclude that the higher compression ratios affect the results of QCA in a negative sense. In conclusion, the use of lossy data compress ion with JPEG or LOT compression schemes al ratios 5, 8 and 12 must be discouraged for QCA.