Quantification of mitral flow by Doppler color flow mapping.

This study was performed to develop and validate Doppler color flow methods for quantifying forward transmitral flow rates and volumes with isovelocity aliasing contours. We undertook computer modeling of flows and studied an animal model with strictly controlled mitral flows. Finite element analysis was first used to establish the isovelocity surface contours reconstructed from the magnitudes and directions of the velocity vectors proximal to the normal mitral orifice. We modeled finite element-simulated Doppler color flow isovelocity surfaces and computed non-angle-dependent simulated isovelocities to compare them. Then 24 pharmacologically induced hemodynamic states in six sheep in which mitral regurgitation had been previously created surgically were studied. Three methods were used for peak flow (PF) computation: (1) the classic hemispheric methods: PF = 2 pi r2.aliasing velocity; (2) a modified hemispheric method: PF = 2 pi r2.aliasing velocity Vo/Vo-aliasing velocity; and (3) a new segment of sphere method: PF = pi p2.aliasing velocity, where p is the chord from the zenith of the first aliasing contour to the circumference at its base. Mean volume flow was also calculated in combination with phasic flow information from continuous-wave Doppler echocardiography: mean volume flow = PF.VTI/Vmax.heart rate, where VTI and Vmax are the velocity-time integral and maximal velocity of mitral inflow by continuous-wave Doppler echocardiography. Compared with the flow rates obtained by electromagnetic flowmeters, different correlations and agreements were achieved for these methods. Correlation (r = 0.86) and agreement were best for the segment of sphere method for computation of forward mean volume flows in our model. Color flow Doppler quantitation with a segment of sphere or modified hemispheric method appears applicable for quantification of forward transmitral valve flow rates and volumes with reasonable accuracy.