| dc.description.abstract | In recent years, high-intensity focused ultrasound (HIFU) has commonly been applied in non-invasive tumor therapy, such as to treat uterine fibroids or prostate tumors. However, respiration may cause tumor displacement such as liver tumor, which may lead to error in localization or inadequate thermal effects on the tumor. The goal of this research is to develop an ultrasound-imaging guided robotic HIFU ablation system for tumor treatment with a respiration and displacement compensatory mechanism. The system integrates the technologies of ultrasound image assisted guidance, robotic positioning control, and HIFU treatment planning. With the assistance of ultrasound image guidance technology, the tumor size and location can be determined from ultrasound images as well as the robotic arm can be controlled to position the HIFU transducer to focus on the target tumor.
According to the correlation between the measured displacements of the heaving chest and the target tumor, a respiration simulation device was designed, which used a phantom and a cam-driving mechanism to simulate displacements of the tumor and of the heaving chest. Then, a polynomial function of tumor position relative to the position of the heaving chest was generated. After the coordinate frames of the robotic arm, optic tracker and tumor phantom had been registered, the robotic arm was able to guide the HIFU probe to track and ablate the target tumor automatically and synchronously by inputting the displacement values of the heaving chest.
After the development of the system, several experiments were conducted to measure the positioning accuracy of this system and the results shows either without respiration simulation device or with respiration simulation device. The experiment results show that the average positioning error in the positioning accuracy of the robotic arm is 1.01±0.34mm, and the average positioning error in positioning accuracy of the ultrasound-imaging guided robotic HIFU system with ablating a phantom is 1.32±0.58mm, and the target point becomes white coagulation lesions, which means this system is confirmed its possibility and accuracy. With the respiration device, the average positioning error in the single-point tracking experiment was 1.72 ± 1.26 mm, while the ablation temperature was stabilized at 80°C, which was enough to kill tumor cells. Furthermore, the average positioning error in the cross-section ablation experiment was 3.04 ± 1.24 mm, and the white coagulated lesion in the area of the planning route was obvious, which means the target area successfully ablated.
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