Research About Fiber Optic Hydrophone For HIFU Field Measurement And Respiratory Gating Application In HIFU Therapy

High intensity focused ultrasound (HIFU) technology as a non-invasive treatment way have been used in tumor disease,that will make the ultrasound gather at the target region and under the thermal effects, cavitation effects, mechanical effects of ultrasound the lesions could be destroyed while the tissue out of the target region would not be destroyed. In recent years, High intensity focused ultrasound has become the research focus of acoustics and medical field. Although the HIFU technology has a great development, the challenge also around with it. There have tow point questions, the one is how to measure the acoustic energy distribution of HIFU sound field precisely, the other is to eliminate the influence in HIFU influence in HIFU treating effectively.In this paper, the purpose is to under the condition that HIFU sound field can not be measured and analyzed with the existing techniques people have mastered. A coated Fabry-Perot fiber-optic hydrophone formed by Parylene for the measurement of High intensity focused ultrasound signals is presented. The hydrophone has simple structure, high resolution, and could detection of HIFU field. This article analyzed the characteristics of high intensity focused ultrasound field,described some methods of detection of HIFU field, and also made the comparison in these methods, using the optical fiber sensing technology for HIFU field measurement is presented. Fiber-optic sensors offer several outstanding advantages, including high resolution, capability of responding to a wide variety of measurands, immunity to electromagnetic interference, small size and light weight, and resistance to harsh environments. Through analyzed the characteristics and the types of the optical fiber sensors, compared several detection of fiber type at the same time, selected based on principle of Fabry-Perot fiber-optic sensors, design the measuring high intensity focused ultrasound sound field system. A coated Fabry-Perot fiber-optic hydrophone formed by Parylene for the measurement of HIFU signals is designed and manufactured, its working principle is discussed at the same time.Based on the Fabry-Perot fiber-optic hydrophone, a HIFU field detection system has built in the paper. The experimental results showed that the developed Fabry-Perot fiber-optic hydrophone can accurately sense the ultrasonic sound, the non-linearity of the output voltage of the Fabry-Perot fiber-optic hydrophone relative to the voltage applied to the ultrasonic transducer is less than 0.01, and the results sensed by the developed Fabry-Perot fiber-optic hydrophone agree with those sensed by the PVDF needle hydrophone. In this paper, aimed at that the organ of displacement caused by breathing could affect the precision of the target of orientation and also the safety of the therapy during the routine treatment. Using the respiratory gating to improve the accuracy of focal point positioning during HIFU therapy is presented. The experiment system of HIFU ablation based on breathing gated control using piezoresistive micro-breathing sensor is designed. The system takes single—chip microcomputer 80C51 as core processor that communicates with PC via full-speed interface chip PDIUSBD12 and is programmed by Microsoft Visual C++ 6.0 according to control the output of HIFU equipment in which the characteristics of respiratory signal. HIFU ablation based on breathing gated control using piezoresistive micro-breathing sensor were applied to the rabbit liver in vivo, which were compared with the normal HIFU ablation procesure for the difference in coagulative necrosis produced under the same ultrasound intensity and ablation duration. The rabbits were executed immediately after HIFU ablation to investigate lesions inside the liver. Results showed that the biological focal region using breathing gated HIFU ablation was 4.5 mm×2 mm at the largest sectional plane, while that using normal HIFU ablation procesure was 9 mm×2.5 mm. The experimental indicates that the respiratory gating could eliminate the influence of the accuracy of focal point positioning during HIFU therapy.