| AimsThe study aims at exploring issuses during the application of high intensity of focused ultrasound (HIFU)as follows:1. Threshold dosage of HIFU to produce coagulated necrosis;2. Relationship between the area of the biologic focal region(BFR) and HIFU dosage;3. Relationship between the temperature of the focus and HIFU dosage;4. Charater of targeted region on ultrasonogram, and its change along with the observing time. relationship among the grayscale changes of targeted region , HIFU dosage and the temperature of the focus;5. To get the best time to examine the ultrasonogram;6. Relationship between the area of BFR and the targeted region in ultrasonogram. Materials and methods:1.Exprimental devices: Model JC focused ultrasound tumor therapeutic system,abbreviatedas Haifu Knife, developed and produced by Chongqing HIFU Technology Co,Ltd, was applied in the expriment.The equipment integrates two transducers, one is imaging probe for localization and monitoring. The other is treatment head operating at a frequency of 1.6MHz with a focusing inclination of 68.60,and having a fixed acoustic focal region of 0.62mm×0.62mm×4.1mm. At the focus, ISATA ranged from 0 to 27000 W/cm2.The temperature measurement system comprises a needle thermocouple with a diameter of 0.7mm, a ZXJ-8 intelligentized auto digital examing instrument and a computer with data acquisition software for automatically acquiring and displaying temperature vs time.2.Parameters: The bovine liver was irradiated by different acoustic powers(65.44W,81.8 W,98.16 W,114.52 W,130.88 W,147.24 W,163.6 W,179.96 W,196.32 W),and under each acoustic power,the exposure time duration was from 1～20 seconds; keeping the depth at 20mm. 3.The air containing level of circulating degassed water was less than 3 ppm in the container.4.Material: Fresh bovine liver tissue samples in-vitro,were immersed in 0.9%NS,and then degassed 25 minutes for application.5.Methods:⑴ Put the thermal probe into the center of focal area under the monitor of ultrasonography.⑵ The process of irradiation to monitor the whole irradiation process by ultrasonogram, and to gather the images of targeted region on ultrasonogram before and at various times(0,5,10,15,30,45,60,90,120,180,240,300 S) after HIFU irradiation; at the same time,to measure the temprature at the focus.⑶ To anatomise the bovine liver after HIFU irradiation ,to measure the diameter of the coagulative area , take photos using digital camera.⑷ We measured and analyzed the grayscale and the area of target region on ultrasonogram through a software —GrayVal(V1.0) . Results:1.When the acoustic power was equal to or higher than 179.96W, the threshold time to induce coagulative necrosis is 1 second; but when the acoustic power was lower than 65.44W, the threshold time to produce coagulative necrosis was about 7 seconds. In the range of 65.44～179.96W, the acoustic power increased 16.36W, the time to produce coagulative necrosis was 1～2 seconds prolonged.2.When the acoustic power was lower than 130.88W, the diameter ratio of longitudinal to horizontal was less than 3; the change of BFR form was minimal, when the acoustic power was higher than 130.88W, thediameter ratio of longitudinal to horizontal changed fast in first 5 seconds, and then lower along with the time prolonged, finally kept relatively stable.3.The BFR increased as the exposure time prolonged; the BFR didn't change obviously within 6 seconds when the acoustic power increased, but when the exposure time was over 6 seconds, it increased along with acoustic power increase.4.The equation of BFR and HIFU dosage we concluded from the study was : y=0.0164X1.0591 ,(R2=0.9238,P<0.05).5.When the acoustic power was lower than 98.16W,the threshold time to get the peak temperature were 15～18s; When the acoustic power was higher than 98.16W and 196.32W, the threshold time were 10～12S, 8～10S respectively. When the acoustic power was equa...
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