Accuracy of Measurements of Flow Velocity by Pulsed and Continuous Wave Doppler Echocardiography: An In-Vitro Study
Takahiro Shiota, Dag Teien, Roben Weintraub, Sage Ewing, You-Bin Deng, James Conti, David J. Sahn. Oregon Health Sciences Univ, Portland, OR
Presented by: Takahiro Shiota
Flow velocity (VEL) estimation by Doppler echocardiography has been widely accepted clinically. To determine the accuracy of Doppler measurement of flow VELs compared to those from a precisely calibrated pulsatile Doppler phantom (EchoCal CD 10 Dynatek Laboratories Inc.) designed as a “Gold Standard”, we evaluated a total of 6 commercially available echo-Doppler systems with 9 pulsed (PW) and 4 continuous wave (CW) Doppler transducers. Actual flow VELs ranged from 30 cm/sec to 150 cm/sec for PW tests, 300 to 400 cm/sec for HPRF PW and 50 cm/sec to 525 cm/sec for CW evaluation. For all systems a fixed transducer interrogated pulsatile flows oriented parallel to the sampling direction. For the total of 113 measurements from the echocardiographic system PW tracings (measured from modal VEL) and CW tracings (measured from peak VEL), excellent correlations existed between measured (y) and actual flow VEL (r=0.99, y = 0.98 x +4.1). The mean difference between measured and actual flow VEL was 1.4 cm/sec with a standard deviation of 5.5 cm/sec and 105 out of 113 (93%) measurements were within 2 SD of the mean. When measuring the lowest flow VELs using low frequency transducers (3.5MHz): however, a tendency for overestimation was noted for all the systems (up to 14 cm/sec or 28% of VEL). On the other hand, when measuring high flow VELs using CW, a tendency for underestimation was observed for all systems (up to 19 cm/sec or 4% of VEL). These differences, however, would still not substantially alter clinical decisions based on Bernouli calculations. High PRF Doppler showed substantial accuracy for mid-range flows. A generally satisfactory agreement between measured and actual flow VEL was found for all systems in our study. The minor discrepancies noted are probably of little clinical importance except when Doppler is used for making absolute rather than ratio measurements related to defining low VEL (eg: pulmonary vein or trans-mitral) flows. At these times, the highest frequency transducer usable should be chosen.