| Image-guided thermal ablation technique is one of curative treatments for liver cancers, furthermore, a clinically promising method with multiple image fusion and three dimensional visualization navigation applied for preoperative planning, intraoperative positioning and postoperative evaluating in ablation treatment for hepatic tumors would play a key role to achieve the goals of precise ablation, in order to improve clinical outcomes and decrease local tumor progression. The software platform of image fusion and three dimensional visualization navigation based on electromagnetic tracking system has been successfully employed in advanced preoperative planning and accurately postoperative evaluation in our previous studies with several obvious merits including improvement of completion rate in first treatment session and reduction of therapeutic sessions. In addition, local tumor progression decreased because the technique with three dimensional visualization is a better way than two dimensional imaging for distinguishing a completely curative ablation.Real-time precisely intraoperative navigation based on three dimensional visualization is one of core operations to perform an ablation procedure for patients. In the application of intraoperative navigation using image fusion and three dimensional visualization, some related basic and clinical researches have been performed and accumulated initial experiences in our previous studies, such as ablation treatments for hepatocellular carcinoma navigated by image fusion between ultrasound (US) and computer tomography (CT) or magnetic resonance imaging (MRI). But, several core techniques are essential to further explore:(1) Puncturing was guided by the combination of two dimensional US and three dimensional reconstructed image and real-time three dimensional navigation was not employed; (2) The registration between the magnetic coordinates and imaging coordinates of three dimensional reconstruction is a time-consuming operation during ablation procedure and automatic registration of navigation coordinates with automatic recognition technique in medical imaging is necessary to develop; (3) A electromagnetic tracking microwave ablation needle with a mini magnetic sensor located in the shaft and closed to needle tip was not applied and the location of the ablation needle was not monitored in real-time at procedure; (4) The problems including the distortion of target organs and tumors due to puncture and their movement following breathe would decrease the accuracy of puncturing. Therefore, a software platform of microwave ablation for liver cancers navigated by real-time three dimensional visualization based on electromagnetic tracking system and with automatic fusion and registration among multi-modality image has been developed under the cooperation of the teams in three institutes including Tsinghua University, Beijing Institute of Technology and Chinese PLA General Hospital. Though the three dimensional navigation in the platform was performed using free-hand technique, the accuracy of puncturing could be further improved together with the assistance of medical robot and training period of physicians majored in ablation guided by imaging would decrease in the future.Before the platform is connected with medical robot, it is extremely important to establish a comprehensive method to evaluate and verify its precision. Its feasibility, convenience at operation and accuracy would be evaluated by phantom and animal experiments to establish technical basis for the combination between the platform and medical robot. The brief instruction of the three parts in this study were listed as follows.The first important part is functional design of the platform and development of electromagnetic tracking microwave antenna. The navigation platform based on the electromagnetic tracking system includes multi-modality image fusion, intraoperative navigation of three dimensional visualization, fast automatic registration of navigation coordinates and advancement navigated by three dimensional visualization in real-time. Electromagnetic tracking microwave antenna with a mini magnetic sensor located in the shaft and closed to active tip is one of essential instruments to perform precise ablation for liver cancers navigated by the platform. A kind of microwave antenna with these functions has been designed and developed by Nanjing Kangyou Microwave Institute and our team. It can be used in magnetic field and with advanced materials and manufacturing process.The second important part is evaluation of registration precision in the navigation platform. An Aurora 6DOF References is one of important hardware tools for registration in electromagnetic tracking system and establishes reference basis for target coordinates including the ones of CT, US and needles. The experiments in the study with a rigid model was designed to evaluate the accuracy of registration in space due to its error would lessen the preciseness of the platform, and accurately spatial automatic registration between imaging and magnetic coordinates was verified. The good automatic registration between magnetic coordinates and three dimensional reconstruction imaging coordinates has been observed by the error evaluation experiments of Aurora 6DOF References. The function of fast registration between electromagnetic tracking microwave antenna and an Aurora 6DOF Probe has been accurately verified according to needles registration experiment between the two needles of Aurora 6DOF Probe and the electromagnetic tracking microwave antenna. After registration, a small but not negligible error with the range from 0.31mm to 1.17mm occurred when the antenna was moved to the six directions in magnetic field, so the registration between an antenna and the Probe would be recommended as a standard step before advancement at intraoperative navigation in further animal experiments and clinical applications.The last but not the least is evaluation of puncture precision in the navigation platform. The feasibility, operating convenience and accuracy has been certified through a comparative experiment of phantom puncture procedures performed by two operator groups with three advance depth, two stages and two guidance techniques between three dimensional visualization and two dimensional US. The experience requirement for operators decreased and the confidence to finish the experiment in the group of poor experience enhanced in the puncturing procedure of three dimensional navigation. The accuracy of shooting at the targets in all operators was 88.9%(48 out of 54). The registration time, puncture time and puncture errors between the platform and a commercial software (Volume Navigation, LOGIQ E9, GE Company, USA) of image fusion and volume navigation have been shown no significant differences in a comparative animal study of in vitro porcine liver puncture. The method of precision verification and quantitative evaluation in animal experiments for three dimensional navigation platform has been established and the mean error of puncture navigated by three dimensional visualization technique was 1.64±1.30mm.As a conclusion, through evaluation of the feasibility, operating convenience and accuracy of the platform, comprehensive methods for precision test and evaluation at in vivo animal experiences and clinical applications have been established in the present study, and will provide technique foundation to precision evaluations, verification for the further combined system of the navigation platform and medical robot. |
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