Influence of instrument settings on flow signal and background noise in power Doppler US - An experimental study using a flow phantom with hyperechoic background

OBJECTIVE. TO determine the influence of various power Doppler instrument s ettings on intensities of flow signal and background noise in flow with a t issue-equivalent phantom. METHODS. Power Doppler images were obtained with changing wall filter level (low, medium, high, and maximum), pulse repetition frequency (PRF; 500, 70 0, 1000, 1500, 3000, and 6000 Hz), and Doppler gain (60%, 70%, 80%, 90%, an d 100%) at different how velocities (13.3, 26.5, and 49.8 cm/sec). To make a quantitative comparison of different settings, the authors measured the i ntensities of flow signal and background noise in obtained power Doppler im ages using the scanner and a computer program, calculated signal-to-noise d ifference (SND; intensity of how signal - intensity of background noise), a nd evaluated the relation between SND and power Doppler settings. RESULTS. The intensities of flow signal and background noise were proportio nal to flow velocity and power Doppler gain but were inversely proportional to PRF and wall filter level. At constant wall filter level (medium), chan ges of PRF and Doppler gain to the same directions resulted in a high SND. At constant PRF (1000 Hz), changes of wall filter and Doppler gain to the s ame directions also resulted in a high SND. However, at constant Doppler ga in (80%), a high SND was obtained with changing wall filter level and PRF t o the opposite directions. CONCLUSIONS. Three Doppler instrument settings-wall filter level, pulse rep etition frequency, and Doppler gain-have reciprocal influences on SND.