Doppler color flow "proximal isovelocity surface area (PISA)":  an alternative method for estimating volume flow across narrowed orifices, regurgitant valves, and intracardiac shunt lesions.
Gardin
J M
JM
D001783:Blood Flow Velocity; D015150:Echocardiography, Doppler; D006349:Heart Valve Diseases / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans