Power Doppler imaging is a commonly used method for the detection of flow. The direction of flow is lost with power Doppler, but it has greater sensitivity to flow compared to velocity estimation techniques. Power Doppler imaging can be degraded if thermal noise is large or if slowly moving reverberation clutter passes through the wall filter. We have developed a power Doppler imaging technique, based on the same principles as power Doppler, but which uses the coherence of backscattered blood signal rather than the complex backscattered signal. This technique, called coherent flow power Doppler (CFPD), is less sensitive to clutter-based signals and thermal noise. We are developing enhanced flow detection methods based on CFPD through simulation, phantom, and in vivo experiments.
Signal processing path of CFPD and PD. For both CFPD and PD, RF channel data are first (a) acquired at one focused lateral location at a fixed PRF, and then (b) time delayed. For CFPD, the delayed data are (c) high-pass filtered across the ensemble length, and then (d) processed with the SLSC method. (e) A power estimator is used to produce one A-scan, and the whole process is repeated for all lateral positions to produce one Doppler image frame. For the PD method, the delayed data are (f) summed across the receive aperture, and (f) high-pass filtered across the ensemble length. (h) A power estimator is used to produce one A-scan, and the whole process is repeated for all lateral positions to produce a Doppler image frame.
CFPD (left) and PD (right) images of 11.5 mm/s flow in the phantom experiments with ensemble lengths of (a) 3, (b) 5, (c) 11, and (d) 13 acquisitions. The scale bar on the right corner indicates 4 mm, and the colorbar has units of dB. The dynamic range is 30 dB for all images. The figure CFPD images show better SNR and lower background noise than PD. The PD image suffer from higher background noise at deeper depth.