Power Doppler US: evaluation of the morphology of stenoses with a flow phantom.

PURPOSE To determine the importance of technical settings at power Doppler ultrasonography (US) for the evaluation of stenoses. MATERIALS AND METHODS A computer-controlled phantom was used to induce a reproducible flow across a calibrated 71% stenosis in an 8.4-mm-diameter tube. Two transducers, 2-4 and 5-10 MHz, working at depths of 3.0 and 11.5 cm, respectively, with different beam angles (40 degrees, 60 degrees, and 90 degrees ), were used to simulate evaluation of pulsatile flow across normal and stenotic vessels in various conditions. For each condition, gain, pulse repetition frequency, and wall filter were progressively turned from low to high values. Two observers measured in a blinded fashion the apparent lumen of the stenotic and normal vessels on longitudinal and transverse images with the use of power Doppler US. RESULTS When the high-frequency transducer was used, gain significantly affected both stenotic and feeding vessel measurement, whereas pulse repetition frequency and filter only affected feeding vessel evaluation. When the low-frequency transducer was used, all factors, including flow velocity and beam angle, played a significant role (P <.001). In most conditions, overestimation of the lumen and underestimation of the lumen of the feeding vessel led to severe underestimation of the degree of stenosis. CONCLUSION Power Doppler US cannot be used to measure stenoses accurately. Underestimation of the degree of the stenosis was significantly higher with the low-frequency probe than with the high-frequency probe.