PISA geometry

View	Zoomed colour Doppler of the regurgitant orifice, variance mapping off, baseline shifted in the direction of the jet.
Timing	Colour frame at the time of maximal regurgitant jet velocity by CW.
Caliper / trace	Radius from the first aliasing contour (abrupt colour change) to the vena contracta, along the centreline of the convergence.

Example

Schematic hemispheric isovelocity shells above a regurgitant orifice with the radius drawn from the aliasing contour. — Radius from aliasing contour to orifice; hemisphere assumed. (Schematic drawing (E/e′ureka), not a patient image)

Correct example

Baseline shifted (down for MR into the LA on TTE) so that a well-defined hemisphere appears; radius measured to the orifice, with dark zones of perpendicular flow marking the orifice position; EROA = 2πr²·Va / peak velocity, RVol = EROA × VTI.

Common error

Measuring a flattened or constrained convergence as if hemispheric, taking the radius on a frame that does not match peak velocity, or forcing the method on an elongated functional orifice.

Effect on interpretation

The radius is squared, so geometry errors dominate; non-hemispheric or elongated convergence underestimates flow and EROA, and a conical orifice plane (TR, tenting) means the convergence covers more than a hemisphere. If a hemisphere cannot be obtained, the method is not reported.

Why

Flow accelerates toward the orifice in concentric isovelocity shells; colour aliasing exposes one shell whose surface area times its velocity is the instantaneous flow rate.