Study Of The Temperature Rise Induced By A Focusing Transducer With A Wide Aperture Angle On Biological Tissue Containing Ribs

High intensity focused ultrasound (HIFU) is an important technology of modern medicine physical therapy for cancer treatment. The treatment principle is to focus sound energy generated by a large ultrasonic focusing transducer to achieve a high temperature in a focal area in a short period of time, causing tumor tissue to undergo thermal coagulation necrosis.A focusing transducer with a wide aperture angle is a spherical-shell focusing transducer with a spherical half-angle greater than 16.6°. Because such a wide angle focusing transducer has a larger radiating area, stronger focusing effect, smaller focal area radius and better penetrability than that of a small angle focusing transducer, a greater temperature rise can be generated within a tumor while reducing damage to other normal tissues. High frequency ultrasound has better directivity and most of the sound energy can be focused on a target area without affecting surrounding tissues by accurate control of the ultrasonic focus, therefore it can realize noninvasive treatment. In practical applications, a sound wave generated by the transducer will pass through multiple biological media before reaching tumor tissue, and it is difficult to avoid reflection and scattering of sound energy because of the mismatch of acoustic impedance between different media, thus affecting the sound field of the target area, and distorting the sound field accordingly. Particularly in the treatment of liver cancer, the presence of the ribs can greatly influence the sound and temperature field, and ultimately affect the efficacy of the treatment. In early clinical treatments, surgical removal of ribs was often used to prevent reflections of ultrasound energy from affecting the stability of the sound field. Consequently, effective prediction of the distribution of the sound and temperature fields behind the ribs becomes very necessary in order to realize noninvasive treatment.In the paper, we used the SBE model to calculate the sound field produced by a focusing transducer with a wide aperture angle to obtain heat deposition, and then solved the Pennes bioheat equation to obtain the resulting temperature field in a biological tissue with ribs. Study the temperature rise induced by a focusing transducer with a wide aperture angle on biological tissue containing ribs and the effects of rib parameters on the temperature field.