| BACKGROUND AND PURPOSE HIFU (High Intensity Focused Ultrasound) is one of the most effective and promising non-invasive cancer treatment technologies. Ultrasound power could be concentrated and penetrated into biologic tissues, which make it possible to introduce low power ultrasound into human body and concentrate into the target where the ultrasound power is intensively high. Biologic effects of HIFU would coagulate target tissue in a very shot time while keeping surrounded tissue safe (thermal effects by high temperature, cavitation effects, and mechanical effects, etc.). No notable damage would be caused nearby normal tissues. The application of HIFU in cancer treatment is accepted widely by domestic and international researchers in recent years. However, with the development of technologies, HIFU treatment equipments should be improved according to clinical requirements.Compared with traditional HIFU cancer treatment machines, our self-developed serial-parallel robot has such merits as lighter structure, lower cost, faster response and larger workspace. Besides, traditional ultrasound transmission profile is static and the ultrasound power would accumulate along transmission trajectory. Inevitable damage would be caused along the trajectory. Whereas,recommended HIFU treatment robot is able to do cone like movement according to driving commands so that the ultrasound power could be distributed in a greater volume and tissue interface where it goes into the patient body. Side effect could be reduced by such treatment scheme without any loss in treatment efficacy, especially for on acoustic interfaces. Such design is supposed to be able to offer much better outcome in clinical HIFU cancer treatment.In vitro and in vivo tissue ablations have been carried out by fixed point HIFU pulse radiation with the help of self-developed cancer treatment robot. The objective of this research is to study the positioning accuracy of HIFU focus in different tissues, HIFU efficacy in tissue ablation and discuss the related factors. Preliminary evaluation has been given for the efficacy of US monitoring and experiment data have been obtained for possible future clinical applications. This research consists of two parts:Part 1. Experimental Study on damage effects in Liver tissue in vitro by 3D-guided HIFU Treatment Parallel Connection to RobotThe objective of this study is to assess in vitro fixed-point ablation efficacy and related affecters in porcine liver with ultrasound transducer doing cone like movement on studied robot. Both transducer movement modes of static position and cone-like rotation have been studied at acoustic focus power of 2000W/cm2. Radiation focus depths have been set to be 10mm and 20mm from the porcine liver surface. Radiation time has been set to be 5s, 10s, 15s and 20s respectively. Variables measured include the volume of coagulated necrosis and the distance between necrosis and tissue surface. Target tissues have been examined pathologically. Comparison has been carried out on the ablation efficacy between data from the group of cone-like rotation transducer and the group of static position transducer. Biological effects of radiation focus depth and radiation time have also been analyzed.Results(1)Radiated HIFU target is a well-delineated gray coagulated necrosis area.(2)With the same radiation dose, there's no notable difference in coagulated necrosis volume between two groups (P>0.05).(3)There's no notably difference between preset depth and central coagulated necrosis depth (P>0.05).(4)Coagulated necrosis by static HIFU radiation increases with the radiation time under the same radiation power and depth. Coagulated necrosis by fixed HIFU radiation decreases with radiation focus depth under the same radiation power and time.Part 2. Experimental Study on damage effects in Liver tissue in vivo by 3D-guided HIFU Treatment Parallel Connection to RobotLiver parenchymas of 14 canines have been extracorporeal radiated by static positioned transducer of pulsed 2000W/cm2 HIFU radiation by recommended robot. Radiation targets have been set to be 3cm and 4cm deep from the skin. Treatment time is set to be 6min, 8min, and 10min respectively. In vivo liver parenchyma has been treated and B-scanning image of the target has been examined immediately, 2 min after, and 5 min after respectively. Anatomic coagulated necrosis volume has been examined after HIFU radiation and maximal dissection area has been recorded. Coagulate necrosis and nearby normal tissue has been examined for the histological study of static HIFU ablation in liver in vivo and related affecters. Preliminary evaluation has been given for US imaging in HIFU treatment supervising.Results(1)Target echo would be notably strengthened after HIFU radiation. The area of echo increases with the time of radiation. Under the same radiation dose, immediate strong echo area on B-scanning image after HIFU radiation is notably greater than actual anatomic coagulative dissection area. There's a significant difference between them (P<0.05). However, there's no significant difference between maximal actual anatomic dissection area and strong echo area on B-scanning image 2min and 5min after HIFU radiation (P>0.05).(2)Grey coagulated necrosis area has been observed in target area in tissue after HIFU radiation, bounded by a dark red blood congested cone that has a clear border with nearby normal tissue. Biologic focus volume increases with radiation time under the same radiation power and depth. Biologic focus volume decreases with radiation depth under the same radiation time. Part 3: Experimental Study on damage effects in different kinds of tissue in vivo by 3D-guided HIFU Treatment Parallel Connection to RobotKidney and muscle tissue in canine has been processed in vivo by 2000 W/cm2 pulse HIFU by recommended robot. Radiation target has been set to be 3cm away from the skin in kidney and muscle respectively, and radiation time has been set to be 6min. Considering about the experiments in Part II, area of target echo on B-scanning image has been examined in addition to anatomic volume of coagulative necrosis. Histological examination has been carried out after HIFU radiation on coagulative necrosis and surrounding boundary tissue. Static transducer ablation effects on different kinds of tissues have been evaluated under the same treatment parameters on recommended robot.Result Strong echo areas are (471.40±56.20) mm2,(117.16±16.89) mm2,(881.82±32.54) mm2 respectively in canine liver, kidney and muscle tissues in vivo. Acoustic power is 2000W/cm2. Radiation time is 6min. Radiation depth is 3cm beneath the skin. Biological focus volumes have been examined to be (3 243.49±243.79) mm3,(608.28±73.55) mm3,(7 886.82±165.64) mm3 respectively. There's notably difference in the difference of strong echo area on B-scanning image and actual biological focus area in different kinds of tissues in vivo experiments (P<0.05). From big to small size, the sequence of difference is the tissue of muscle, liver and kidney.CONCLUSIONS:(1) Recommended HIFU treatment robot is able to introduce exact and effective ablation in tissue by swing movement of transducer.(2) Coagulative necrosis takes place in radiation target and has a clear border with nearby normal tissue. The size of biologic focus area is determined by the acoustic and biologic characters of tissues.(3) Ultrasound imaging is an effective method for accurate evaluation of HIFU introduced ablation in biologic tissues.
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