The<unk>  <unk>  technique can be used to estimate the flow across the regurgitant valve together with the Effective Regurgitant Orifice<unk>  (EROA).
The technique is an application of the continuity principle with the underlying assumption being that the flow at the hemispheric first alias<unk><unk>  is equal to the orificial flow at the same time in the cardiac cycle.
In order to measure these indices of regurgitation it is necessary to perform both continuous wave Doppler (CWD)  and colour Doppler analyses of representative cardiac cycles.
Vmax (the peak velocity of the regurgitant flow signal) is measured with CWD.
Colour Doppler is then used to measure the radius (RA1) of the first aliased hemispheric shell at a Nyquist limit (Scale Value) typically in the range 30 - 40 cm/sec (VN).  
Grade             <unk>  Radius(mm)
Mild:              < 3.5
Moderate:          3.5 - 7.5
Moderately Severe: 7.5 - 14.5
Severe:            > 14.5
Grade             <unk>  Q
Mild:              < 30 ml/sec
Moderate:          30 - 130 ml/sec
Moderately Severe: 130 - 500 ml/sec
Severe:            > 500 ml/sec
Grade              EROA(mm2)
Mild:              < 20
Moderate:          20 - 29
Moderately Severe: 30 - 39
Severe:            > 40
According to Kolev et al, the<unk>  technique may be particularly appropriate for the estimation of the severity of mitral regurgitation in the patient with an eccentric regurgitant jet.
Proximal isovelocity surface area
Volumetric flow rate
Pressure gradient 
A-a gradient
Angular resolution
Pulsatile flow
Guidewire core diameters
Venous translucence