Echocardiography Techniques III Exam 1 Practice 2026 - Free Echocardiography Practice Questions and Study Guide

In PISA, the flow is estimated from the hemispherical shell of converging flow near the regurgitant orifice. The instantaneous flow rate across that surface equals its area times the velocity at the aliasing surface. The surface area of a hemisphere is 2πR^2, where R is the radius of the aliasing isovelocity shell. Multiply by the aliasing velocity (the velocity at that surface) to get Flow = 2πR^2 × aliasing velocity. This is why the correct expression includes both the hemispherical area and the velocity.

The other forms don’t represent the actual flow: πR^2 would be the area of a circle, not a hemispherical surface; 2πR is a circumference, not a surface area; 2πR^2 lacks the velocity term.