How this instrument works
The proximal isovelocity surface area (PISA) method estimates the severity of mitral regurgitation from routine echocardiographic measurements. As blood accelerates toward a regurgitant orifice, it forms a series of hemispheric shells of constant velocity; measuring the radius of one such shell at a known aliasing velocity (the Nyquist limit at which the color Doppler display flips color) gives the flow rate converging on the orifice: 2π times the radius squared, times the aliasing velocity.
Dividing that flow rate by the peak regurgitant jet velocity, taken from continuous-wave (CW) Doppler, gives the effective regurgitant orifice area (EROA) — the functional size of the leak. Multiplying EROA by the jet's velocity-time integral (VTI), the area under the CW Doppler velocity curve for one beat, gives the regurgitant volume: how much blood moves backward through the valve per beat.
This calculator applies the American Society of Echocardiography's 2017 guideline bands for grading severity by EROA — but only the bands for primary (degenerative) mitral regurgitation: mild below 0.20 cm², moderate from 0.20 up to just under 0.40 cm², and severe at 0.40 cm² or above. The same guideline sets different EROA cutoffs for secondary (functional) mitral regurgitation, which this calculator does not implement — applying the primary-MR bands to a functional-MR study would misgrade it.
This is a specialist instrument for clinicians performing or interpreting an echocardiogram, not a patient self-assessment tool. It performs the PISA arithmetic on numbers a sonographer or cardiologist has already measured from the study; it doesn't measure anything itself and doesn't know whether the jet is primary or secondary, central or eccentric, or whether the hemispheric-shell assumption holds well for a given orifice.
- Enter the PISA radius measured from the color Doppler image, in cm.
- Enter the aliasing velocity (Nyquist limit) the color flow map was set to, in cm/s.
- Enter the peak regurgitant jet velocity from continuous-wave Doppler, in cm/s.
- Enter the regurgitant jet's velocity-time integral (VTI), in cm.
- Read the calculated flow rate, EROA, regurgitant volume, and the primary-MR severity tier (1 = mild, 2 = moderate, 3 = severe).
Worked example — three PISA measurements across the severity range
A PISA radius of 1.0 cm at a 40 cm/s aliasing velocity gives a flow rate of 2π × 1.0² × 40 ≈ 251.33 mL/s. Against a 500 cm/s peak jet velocity, that's an EROA of about 0.503 cm² — at or above the 0.40 cm² threshold, so this grades as severe (tier 3). With a 100 cm VTI, the regurgitant volume works out to about 50.3 mL per beat.
A smaller radius, 0.8 cm, at a 35 cm/s aliasing velocity gives a flow rate of about 140.74 mL/s. Against a 480 cm/s peak velocity, that's an EROA of about 0.293 cm² — between the two thresholds, so this grades as moderate (tier 2). With a 90 cm VTI, the regurgitant volume is about 26.4 mL.
A still smaller radius, 0.6 cm, at a 30 cm/s aliasing velocity gives a flow rate of about 67.86 mL/s. Against a 450 cm/s peak velocity, that's an EROA of about 0.151 cm² — under the 0.20 cm² mild threshold. With an 80 cm VTI, the regurgitant volume is about 12.1 mL.
Questions
What does the PISA method actually measure?
It measures the radius of a hemispheric shell of accelerating blood flow, visible on color Doppler, as that flow converges on a regurgitant orifice at a known aliasing velocity. That radius and velocity give a flow rate, and dividing flow rate by the peak jet velocity (from continuous-wave Doppler) gives the effective regurgitant orifice area — a measure of how large the functional leak is, not a direct anatomical measurement of the orifice.
Why does the severity threshold only apply to primary mitral regurgitation here?
The ASE's 2017 guideline (Zoghbi et al.) sets different EROA cutoffs for primary (degenerative) versus secondary (functional) mitral regurgitation, because the two conditions behave differently and carry different risk at a given orifice size. This calculator only implements the primary-MR bands (severe ≥0.40 cm², mild <0.20 cm²); using it to grade a functional-MR case would apply the wrong thresholds.
What is the aliasing velocity, and where does it come from?
It's the Nyquist limit the color Doppler scale is set to when the PISA radius is measured — the velocity at which the color display flips from one direction's color to the other, creating the visible hemispheric flow-convergence zone. It's read directly off the ultrasound machine's color velocity scale at the moment the radius is captured, not calculated separately.
Who is this calculator for?
Clinicians and sonographers performing or interpreting an echocardiogram — it's a specialist tool that runs the PISA arithmetic on measurements already taken from a study. It isn't intended for patients to self-assess mitral regurgitation from home.
What's the difference between EROA and regurgitant volume?
EROA (effective regurgitant orifice area, in cm²) describes how large the functional leak is. Regurgitant volume (in mL) describes how much blood actually moves backward through the valve in one beat — it's EROA multiplied by the jet's velocity-time integral (VTI), so it also depends on how long and how fast the regurgitant flow lasts during that beat, not just the orifice size.
Does the PISA method have known limitations?
Yes. It assumes a roughly hemispheric, symmetric flow-convergence zone, which holds less well for eccentric jets or non-circular, irregular orifices — common in some forms of primary MR. The ASE guideline presents PISA as one of several complementary quantitative methods, to be interpreted alongside 2D/3D imaging and other Doppler findings, not used in isolation.
Can this calculator diagnose mitral regurgitation or replace the echo report?
No. It performs the specified PISA arithmetic on the four values entered; it doesn't interpret color Doppler images, distinguish primary from secondary MR, or weigh the rest of the study. Any severity grade should be confirmed by the reading clinician against the full echocardiographic and clinical picture.
References
- Zoghbi WA, et al. Noninvasive Evaluation of Native Valvular Regurgitation. J Am Soc Echocardiogr. 2017;30(4):303-371.
- Full guideline text (open access), American Society of Echocardiography
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.