Study Frequency Shift Evaluation of Ultrasound in Fresh and Frozen-thawed Tissues of Cryosurgery by AR Model.

BACKGROUND Noninvasive monitoring of cryosurgery is important for performing precise monitoring of the freezing process in situ and evaluating postoperative effects after therapy. One potential approach is to monitor the normal and freeze-thawed tissues through ultrasonic backscattered signal processing. OBJECTIVE A noninvasive method for cryosurgery monitoring based on the analysis of microstructural characteristics of in vitro porcine liver tissues at different state including normal and freeze-thawed tissues by estimating the center frequency of scatterers (CFS) using the autoregressive (AR) cepstrum of ultrasonic backscattered signals. MATERIALS AND METHODS The method is based on the discrete scattering model described in the tissue characterization literature and the observation that most biological tissues are semi-regular scattering lattices. A total of ten in vitro porcine liver samples were used and freeze by water bath in the experiments. RESULTS Experimental results show that the CFS in porcine liver tissues decreases after pre-frozen and then thawed. CONCLUSION The CFS obtained using this method may be used as a characteristic parameter for tissue characterization in noninvasive monitoring the transition zone between frozen and unfrozen tissues during the surgical therapy, and evaluating postoperative effects.