ASSESSMENT OF STENOSIS SEVERITY USING A NOVEL METHOD TO ESTIMATE SPATIAL AND TEMPORAL VARIATIONS OF BLOOD-FLOW VELOCITY IN BIPLANE CORONAROGRAPHY

The authors present a novel method to estimate absolute blood flow vel ocity in coronary arteries from biplane angiograms. Spatial and tempor al velocity variations are derived giving simultaneously a direct geom etric and an indirect functional index of stenosis severity, stenosis ratio and coronary flow reserve. No prior assumption concerning stenos is geometry is made. Deformable models are used to track a coronary ar tery segment dynamically in three dimensions. A densitometric map is o btained by summing densities across sections at every position along t he previously calculated path and at every time of the cardiac cycle. An advection relationship between density and velocity is observed. Th e spatiotemporal velocity map is a solution of a nonlinear least-squar es scheme. A simulation protocol based on simple geometric conformatio ns and blood flow properties is used to assess numerical stability and immunity towards noise. Predicted results for temporal velocity varia tions are compared with the intracoronary Doppler recordings to test t he model assumptions for basal state and hyperaemia examinations of th e same patient. The stenosis ratio was accurate to within 3% for a sim ulated additive Gaussian noise with a standard deviation of 0.14. The limits of agreement between angiographic and Doppler velocities were - 11.4 and 11.8 cm s(-1) for a peak value of 23 cm s(-1) (basal state) a nd -16.8 and 13.5 cm s(-1) for a peak value of 52 cm s(-1) (hyperaemia ), corresponding to 18 and 3.5% errors on the average peak values and a 16% error on the coronary flow reserve. To summarize, the advection model derivation and its solution are presented. Simulated and experim ental results corroborate the validity of the numerical schemes and su pport clinical applicability.