Development Of A Tissue-mimicing Phantom For Evaluating The Focusing Performance Of High Intensity Focused Ultrasound (HIFU)

【Background and objectives】: It is well known that High Intensity Focused Ultrasound ( HIFU ) has become a new technology for hyperthermal ablation the solid malignancies. And the single coagulation necrosis region induced by HIFU was defined by Wang as Biological Focal Region (BFR). The BFR is the knife point of HIFU to hyperthermal ablating the tumor. So the investigation of the BFR is the guarantee of the effectivity and security of HIFU therapy, and it embodied the focusing performance of the HIFU energy transducer whether the BFR can be controlled. Studies showed that the appearance and area of the BFR were influenced by bionomics of the biological tissue itself and output energy of the HIFU as to one definite transducer. So, if the carrier used to investigate the BFR has the same bionomics, and under the same output energy, the appearance and area of the BFR can reflect the focusing performance of the HIFU energy transducer. The purpose and significance of our study is to develop one tissue mimicking phantom which can be used evaluating the focusing performance of the HIFU energy transducer, and the phantom should has the same acoustic characteristic and thermotic characteristic as the biological tissue; to establish one system to evaluating the focusing performance of the HIFU energy transducer; to advancing the development of the technology of hyperthermal ablation tumors. The objectives of our study is: ① to develop a HIFU phantom which mimicking the soft tissue; ② to measure the acoustic characteristic and thermotics property of the phantom; ③ to explore the variation of the BFR while exposed to the ultrasound with different exposure powers and exposure time. 【Materials and methods】: part 1 The tissue mimicking phantom was made from water,gelatin,some fresh biologic tissue. part 2 1 To measure the ultrasonic parameters of this kind of phantom, including attenuation coefficient by the method of radiation pressure. 2 To measure the thermotics parameters of the phantom, including thermal conductivity, specific heat , fusion point et al under the Measurement meter. 3 To detect the HIFU biological effect of the phantom under the Model JC focused ultrasound tumor therapeutic system, abbreviated as Haife Knife, developed and produced by Chongqing HIFU Technology Co. Ltd (working frequency: 0.7MHz; acoustic power: 200W; focal distance: 135mm; Acoustic focal region: 3×3×25mm3). part 3 1 Experimental device: model JC focused ultrasound tumor therapeutic system. 2 Material: self-made tissue mimicking phantom; fresh bovine liver tissue samples in-vitro, were immersed in 0.9%NS, and then degassed 30 minutes for application. 3 Parameters: the phantom and bovine liver was irradiated by different acoustic powers (180W,200W, 220W); under each power, the exposure time duration was from 2-10 seconds; and the exposure depth was kept at 10mm. 4 Method: ①To monitor the whole irradiation process by ultrasonogram, and to gather the images of targeted region on utrasonogram before and at varioustimes (0,60s) after HIFU irradiation; measured and analyzed the grayscale on ultrasonogram through a software—Grayval (V1.0). ② To anatomise the self-made phantom and bovine liver, then find the largest area of the BFR, to measure the area of the BFR, take photos using digital camera. 【Results】 1 The self-made phantom is sable, has smooth and glossy appearance, well-distributed construction, and good elasticity. 2 We measured the followed values for acoustic and thermal properties: density 1049±2kg/m3; attenuation 0.532±0.017dB/cm(0.8MHz) ,0.612±0.021 dB/cm(1.0MHz); thermal conductivity 0.76±0.08W/m/℃; specific heat 3653±143 J/kg-℃; fusion point154±8℃. 3 The tissue mimicking phantom in vacuum-packed can reserve more longer, but the color of the phantom was changed gradually. The appearance and area of the BFR also changed but the appearance of the BFR is stable in 15 days and the area of the BFR is stable in 60 days after HIFU exposure in the self-made phantom. 4 The appearance...