Slow-time Golay decoding for Doppler detection of high-velocity blood flow

Doppler flow estimation suffers from the weak backscattering from the red blood cells in the vessel. Thus, a novel method is proposed in this study for Doppler detection utilizing Golay-coded excitation to improve signal-to-noise ratio (SNR). Unlike traditional Golay decoding which is limited to low-velocity flow to avoid motion artifact, the proposed decoding is applicable to both high flow velocity and low flow velocity. The analyses show that the main lobe component of Golay code can produce the correct Doppler frequency but the range side lobe counterpart erroneously shifts by half of the pulse-repetition-frequency (PRF). Thus, an optimized decoding filter whose low-pass cut-off frequency is PRF/4 in the slow-time is developed. The PRF/4 filter can retain the main lobe component with Doppler frequency within ±PRF/4 while eliminating the side lobe component outside ±PRF/4. The experimental results demonstrate that the range side lobe level (RSLL) is effectively suppressed by the PRF/4 filter compared to the conventional and the modified methods. In the case of high flow velocity, the color-flow image (CFI) with the PRF/4 filter exhibits accurate estimation of the flow region while the conventional and the modified methods suffer from noticeable side lobe artifacts. In condition, the performance of Golay excitation improves in Doppler detection by using the PRF/4 filter for decoding.