Filtering of ultrasound echo signals with the fractional Fourier transform

The aim of this work was to investigate the use of the fractional Fourier transform as a technique for filtering raw RF ultrasound signals. The results obtained are compared with those obtained using a matched filter based on a measured system impulse response and are shown to be similar. Quantitative comparison of the SNR´s of signals filtered with the fractional Fourier technique and matched filtering are compared and shown to differ. Although the images produced with fractional Fourier filtering have greater contrast than those from matched filtering, the SNR´s are lower. It was found that for the types of signals used in conventional PW ultrasound systems, the optimum transform order for the fractional filtering technique was almost equal to π/2, indicating that the filter will be almost identical to a simple frequency domain band-pass approach. It is concluded that for simple tone-burst based systems, such as conventional PW ultrasound, there is little advantage in using fractional Fourier filtering.