DIRECTIONAL LOW-PASS FILTERING FOR IMPROVED ACCURACY AND REPRODUCIBILITY OF STENOSIS QUANTIFICATION IN CORONARY ARTERIOGRAMS

This Raper concerns the quantification of percent diameter stenosis in digital coronary arteriograms of low spatial resolution. To improve a ccuracy and reproducibility an edge-preserving smoothing method, calle d the directional low-pass filter (DLF), was developed to suppress qua ntum noise by averaging image intensity in a direction parallel to the vessel border. Accuracy of stenosis quantification was assessed by us ing stenosis phantoms. The standard error of the estimate (SEE) was 0. 76 pixel-length (p) without spatial filtering and further reduced to 0 .50 p by DLF; the average deviation as a measure of the regularity Of border definition was also reduced by DLF from 1.00 to 0.68 p (n = 50, P < 0.001). It was shown that the DLF outperformed the conventional m oving average filter and median filter. Reproducibility in terms of in traframe variability was assessed by using coronary arteriograms obtai ned from 10 patients, intraframe variability of the percent stenosis m easurements was reduced from 3.5% to 2.9% by DLF (n = 10, P < 0.005). An analysis of variance showed, however, that the interframe variabili ty cannot be reduced by any of the spatial filters under investigation . The result of this study has provided a guideline for angiographical ly based quantification of percent stenosis under limited imaging reso lution and suggests a new method for improving accuracy and reproducib ility by directional low-pass filtering.