High resolution medical acoustic vascular imaging using frequency domain interferometry

We employed frequency domain interferometry (FDI) for medical acoustic vascular imaging to detect multiple targets with high range resolution. The phase of each frequency component of an echo varies with the frequency, and we can estimate target intervals from the phase variance. This processing technique is generally used in radar imaging. When the interference within a range gate is coherent, the cross correlation between the desired signal and the coherent interference signal is nonzero. Since Capon method works under the guiding principle of output power minimization, the desired signal is canceled by a coherent interference signal. Therefore, we utilize the frequency averaging to suppress the correlation of the coherent interference. The results of computational simulations using a pseudo echo signal showed that Capon method with a frequency averaging technique using a single reference wave presents a higher range resolution than that using a conventional method. In the experimental study the range resolution of FDI with Capon method using a single reference wave deteriorates severely because we approximated the auto-correlation function of the echo to the cross-correlation function of the echo and the reference signal. Therefore we proposed FDI with Capon method using multiple optimized reference waves. The proposed target detection method using optimized reference waves had higher range resolution than that using a single reference wave, and could distinct two target boundaries that lied 0.05mm apart experimentally.