Flow estimation using an intravascular imaging catheter

Coronary flow assessment can be useful for determining the hemodynamic seve rity of a stenosis and to evaluate the outcome of interventional therapy. W e developed a method for measuring the transverse flow through the imaging plane of an intravascular ultrasound (IVUS) catheter. This possibility has raised great clinical interest since it permits simultaneous assessment of vessel geometry and function with the same device. Furthermore, it should g ive more accurate information than combination devices because lumen diamet er and velocity are determined at the same location. Flow velocity is estimated based on decorrelation estimation from sequences of radiofrequency (RF) traces acquired at nearly the same position. Signal gating yields a local estimate of the velocity. Integrating the local velo city over the lumen gives the quantitative flow. This principle has been calibrated and tested through computer modeling, in vitro experiments using a flow phantom and in vivo experiments in a porcin e animal model, and validated against a Doppler element containing guide wi re (Flowire(TM)) in humans. Originally the method was developed and tested for a rotating single elemen t device. Currently the method is being developed for an array system. The great advantage of an array over the single element approach would be t hat the transducer has no intrinsic motion. This intrinsic motion sets a mi nimal threshold in the detectable velocity components. Although the princip le is the same, the method needs some adaptation through the inherent diffe rent beamforming of the transducer. In this paper various aspects of the de velopment of IVUS flow are reviewed. (C) 2000 Elsevier Science B.V. All rig hts reserved.