A deterministic approach to automated stenosis quantification

We developed a new approach to quantitative coronary angiography (QCA), whi ch overcomes several limitations of available programs, such as dependence on operator input; limited tracking ability; fixed correction of the point spread function (PSF);, and different calibration on empty vs. contrast-fil led catheters. The program (Intelligent Images QCA, version 1.4) provides a bsolute reproducibility by deterministic, operator-independent identificati on of the skeleton and the edges of the coronary tree. The algorithm works as follows: application of a matched filter to emphasize selectively the co ronary arteries; adaptive threshold binarization; binary thinning and skele tonization; perpendicular resampling with sub-pixel interpolation; derivati ve filtering; minimal cost edge detection; and automatic identification and quantification of the stenosis, Operator's interaction is restricted to de finition of a region of interest; editing of either skeleton or edges is no t allowed. PSF correction is fine-tuned to the actual frequency response of the imaging chain by calibration on a contrast-filled conical lucite phant om, Catheter calibration is carried out by a second derivative-based edge d etection much less sensitive to the presence of contrast. In vitro phantom analysis (0.5 to 5.0 mm) showed accuracy of 0.028-0.031 mm and precision of 0.054-0.062 mm on nonmagnified images from the angio TV chain and the cine projector, respectively. In vivo evaluation on a series of consecutive dia gnostic angiograms yielded correct contour detection of 70/73 stenoses (96% ); interobserver intraframe MLD variability 0.00 mm; correct tracking of ca theter edges 100%; interobserver variation coefficient of catheter calibrat ion 3.3%; and mean difference of calibration factor on contrast-filled vs. empty catheters 2.7%, This new approach significantly improves reproducibil ity with respect to conventional QCA, maintaining high accuracy, precision, and applicability, Cathet. Cardiovasc. Intervent. 48:435-445, 1999, (C) 19 99 Wiley-Liss, Inc.