Second Department of Internal Medicine Kagawa Medical University
Power, Doppler, Filter, Velocity, Flow
We used a flow phantom to examine the usefulness and potential clinical value of two-dimensional echocardiograms produced using the power Doppler mode, which produces images from the power of the back scatter from Doppler signals. Power Doppler mode images were recorded at four different velocities (15, 20, 35, and 65 cm/s) of steady flow at two different ultrasonic beam angles of incidence, 30˚ and 60˚. Signals obtained using the power Doppler mode were fed into an off-line image-analyzing system as a 256-level gray scale image, and average gray level was measured in the region of interest, which was set at the center of an acrylic tube. At each flow velocity, gray levels measured with power mode correlated significantly with those measured with pulsed Doppler mode (r=0.968, p=0.03). Significant differences were observed between the two angles of the ultrasound beam when flow velocity was relatively low (15, 20, and 35 cm/s), while no significant difference was observed when velocity was 65 cm/s. As intensity of the power Doppler image was changed by the Doppler frequency shift, which was affected by angle of incidence, mode was affected by the filter rather than the number of moving targets. Thus it is important to be aware that, in a clinical setting, power Doppler images are affected by a high pass filter.