Ultrasound Transducer and System for Real- Time Simultaneous Therapy and Diagnosis for Noninvasive Surgery of Prostate Tissue

For noninvasive treatment of prostate tissue us- ing high-intensity focused ultrasound this paper proposes a design of an integrated multifunctional confocal phased array (IMCPA) and a strategy to perform both imaging and therapy simultaneously with this array. IMCPA is composed of triple- row phased arrays: a 6-MHz array in the center row for imag- ing and two 4-MHz arrays in the outer rows for therapy. Dif- ferent types of piezoelectric materials and stack configurations may be employed to maximize their respective functionalities, i.e., therapy and imaging. Fabrication complexity of IMCPA may be reduced by assembling already constructed arrays. In IMCPA, reflected therapeutic signals may corrupt the quality of imaging signals received by the center-row array. This prob- lem can be overcome by implementing a coded excitation ap- proach and/or a notch filter when B-mode images are formed during therapy. The 13-bit Barker code, which is a binary code with unique autocorrelation properties, is preferred for imple- menting coded excitation, although other codes may also be used. From both Field II simulation and experimental results, we verified whether these remedial approaches would make it feasible to simultaneously carry out imaging and therapy by IMCPA. The results showed that the 13-bit Barker code with 3 cycles per bit provided acceptable performances. The measured −6 dB and −20 dB range mainlobe widths were 0.52 mm and 0.91 mm, respectively, and a range sidelobe level was measured to be −48 dB regardless of whether a notch filter was used. The 13-bit Barker code with 2 cycles per bit yielded −6 dB and −20 dB range mainlobe widths of 0.39 mm and 0.67 mm. Its range sidelobe level was found to be −40 dB after notch filtering. These results indicate the feasibility of the proposed transducer design and system for real-time imaging during therapy.