Effect of lossy data compression on quantitative coronary measurements

With the accepted use of (lossy) data compression at low compression factors (2, 3 and 4 on the Philips DCI), the question was posed whether higher lossy compression ratios can also be used without statistically affecting the results of quantitative coronary arteriography. In this study the influence of two data compression schemes (LOT and JPEG) at three different compression factors (5, 8 and 12) on coronary measurements 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 assess the intra-observer variabilities in the obstruction and reference diameters and in the percent diameter stenosis. The results of the first and second measurements in each image were averaged, and from the differences in corresponding images with different compression ratios, the inter-compression variability was obtained. The results show that the intra-observer systematic errors in the absolute diameters are all small (< 0.07 mm), and statistically not significantly different. The intra-observer random errors for the compressed/decompressed series, however, 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 compression ratio of 5 and for the LOT scheme at a compression ratio of 12. The inter-compression systematic errors in the absolute diameter measurements were also small (< 0.07 mm) and not significant, while the random errors were found to be high in the range between 0.23 mm and 0.31 mm. Given the higher intra-observer variabilities for the compressed/decompressed image series as compared to original images, and the fact that all inter- compression variabilities were found to be so high, we must conclude that the higher compression ratios affect the results of QCA in a negative sense. In conclusion, the use of lossy data compression with JPEG or LOT compression schemes at ratios 5, 8 and 12 must be discouraged for QCA.     

Quantitative analysis of left ventricular function from equilibrium gated blood pool scintigrams: an overview of computer methods

An overview is presented on different techniques for data acquisition and analysis of technetium-99m gated blood pool scintigrams. The basic principles for semi- and fully automated boundary detection of the left ventricular activity structure in one or more frames and for the selection of the background region of interest are described. Methods for the computation of global and regional ejection fraction are discussed and comparative data from scintigraphic and contrast left ventricular angiography presented. Finally, an overview of commercially available state of the art computer programs for the computation of global and regional ejection fraction is presented.     

Prognosis and thallium-201 scintigraphy in patients admitted with chest pain without confirmed acute myocardial infarction.

Exercise and rest thallium scintigraphy and exercise electrocardiography were performed after discharge in 158 patients aged less than 76 years admitted with chest pain in whom a suspected diagnosis of acute myocardial infarction had not been confirmed. During a follow up of 12-24 months (median 14 months) there were 10 cardiac events--that is, non-fatal acute myocardial infarction or cardiac deaths. Transient thallium defects and abnormal ST response (that is ST segment deviation or uninterpretable ST segment) during exercise were correlated significantly with an unfavourable prognosis. One hundred and four patients with neither of these characteristics were at lower risk of a cardiac event than the 19 patients with both of these characteristics. The percentages of patients in these two groups without a cardiac event after one year were 98.1 and 78.8 respectively. Thallium scintigraphy, alone or in combination with exercise electrocardiography, can be used to identify groups at high and low risk of future cardiac events, in patients with chest pain in whom acute myocardial infarction is suspected but not found.