Golay-Encoded Pulse-Inversion Subtraction for Real-Time Ultrasound Monitoring of HIFU Therapy

Ultrasound (US) imaging is often used for guidance of high-intensity focused ultrasound (HIFU) treatment due to its high temporal resolution and low cost. However, real-time US monitoring is often hindered when the strong HIFU interference overwhelms the imaging echoes. In this study, a method of Golay-encoded pulse-inversion subtraction (PIS) is proposed to better visualize the change of imaged object during the HIFU treatment. It effectively eliminates HIFU interference patterns in real-time US imaging and also improves the signal-to-interference ratio (SIR). In PIS method, the received imaging echo of positive transmit is subtracted from that of negative transmit to cancel the HIFU component. When Golay excitation is adopted, imaging echo after PIS is further decoded by matched filters for pulse compression. The performance of the proposed method was evaluated through experiments with both PVA phantom and ex-vivo swine liver. Results show that 4-bit Golay transmit can improve the SIR from -15.0 dB of un-coded transmit to 3.5 dB. With PIS, the SIR of 4-bit Golay further increases to 15.9 dB.