Evaluation of HIFU transducer performance

The performance indicators describing the transducer are operating frequency, electroacoustic efficiency, and transmitted sound power. The performance of the HIFU ceramic transducers is described below, and the performance of the four in vitro focused transducers is described separately. (1) Operating frequency of the transducer. Typically, the operating frequency of the transducer is equal to its own resonant fundamental frequency, so that the best operating conditions are achieved for maximum transmit power and efficiency. The ultrasound frequency for treatment is generally low (no more than 5 MHz), the choice of frequency is largely determined by the target depth, and the lower the ultrasound frequency, the stronger the penetrating tissue capacity. According to the technical requirements that must be included in the product standard of high-intensity focused ultrasound therapy machine, the operating frequency of the transducer used in high-intensity focused ultrasound therapy is 0.5~5MHz.

The electroacoustic efficiency of the Pzt8 material HIFU ceramics. For the acoustic lens focusing transducer, since the lens itself absorbs the ultrasonic wave, the generated high temperature easily deforms the lens, and the transducer has low electroacoustic efficiency. The electroacoustic efficiency of a spherical self-focusing transducer is significantly better than that of an acoustic lens focusing transducer, but the creator's material is different and its electroacoustic efficiency is also different. The electroacoustic efficiency of the multi-element self-focusing transducer is relatively high. If the focus of each unit transducer cannot point to the same point, the distribution of the focused sound field parameters is relatively poor.

The transmitted sound power of the HIFU ceramics for lasers medical . It is a physical quantity describing how much the transducer radiates sound energy to the medium sound field per unit time, and its size directly affects the effect of ultrasonic therapy. The damage of the tissue is proportional to the sound power, and the stronger the sound power, the more serious the damage. The transmit power of the transducer generally varies with the operating frequency, and at its mechanical resonant frequency, the maximum transmitted acoustic power can be obtained.

 The distribution of the transducer focused sound field. The performance of the focused ultrasound transducer is inextricably linked to the focus and sound field distribution. Sound field distribution parameters include focal length, focal field morphology, sound field sound pressure distribution, side lobes, etc. These parameters are related to each other to determine the clinical therapeutic effect of HIFU. The focal length determines the effective depth of treatment for HIFU. The depth of treatment of HIFU refers to the maximum depth of the HIFU sound system radiating surface to its focal point in the human body. In human tissues, the liver and kidney lesions are about 20 mm shallow, the prostate lesions are about 150 mm deep, and other human tissues are mostly in the range of 20-150 mm. The focal region shape is also an important parameter of HIFU. For HIFU devices, it is emphasized that the sound intensity at the focus must be high, which requires the focal spot of the focused sound field to be small. If the focal spot is too large, even if the sound power is large enough, the sound intensity at the focal length does not meet the requirements, and the focal temperature of the focal region cannot be raised to 65 or more, which cannot be called HIFU piezoceramic transducer. Sound field sound pressure distribution and side lobes are also an important parameter of HIFU.