| At present,microwave ablation(MWA)has been recognized as the mainstay in the minimally invasive interventional treatment of tumors,which is characterized by fast heating and a large ablation zone.However,it is difficult to accurately confirm the tumor location and distinguish the boundary of the ablation zone in MWA guided by conventional ultrasound and computed tomography imaging.And the match between the ablation zone generated by the microwave ablation antenna and tumor morphology is always low in MWA.In this thesis,we take advantages of magnetic resonance imaging(MRI),including high-resolution imaging,exquisite soft tissue contrast,and arbitrary orientation imaging,and then we mainly overcome the technical difficulties of MWA and apply it to the MRI system.MR-guided MWA can give full play to the advantages of the two techniques to improve the quality of surgery.Focusing on the study of the MR-guided MWA,we designed and built an MRcompatible microwave ablation system,including a microwave ablation apparatus and a microwave ablation antenna.Then,the compatibility of the microwave ablation system was verified at 1.5 T and the study of MR-guided MWA was carried out.The main work included:(1)A design scheme of MR-compatible microwave ablation antenna combining the zirconia tip and titanium alloy tube was proposed.A novel MR-compatible choke antenna was designed based on the conventional dipole and coaxial choke antenna and a novel MR-compatible dual-slot antenna was designed based on the conventional dualslot antenna.According to the finite element numerical simulation method,a physical model was established whose electrical and thermal parameters were wary with temperature.The structure parameters of the two MR-compatible microwave ablation antennas were optimized.Then,the performance of the two antennas in liver tissue was studied,including microwave radiation efficiency,electromagnetic distribution,specific absorption rate distribution,temperature distribution,thermal damage distribution,and the ablation zones generated by the two antennas under different microwave dose control.The mechanical properties of the two MR-compatible microwave ablation antennas,including puncture force,rigidity,and toughness,were tested according to relevant medical industry standards.(2)An MR-compatible 2450 MHz microwave ablation apparatus was developed.The apparatus is designed in accordance with the requirements of the relevant national and pharmaceutical standards.After realizing the functions of the conventional microwave ablation apparatus,such as 0-100 W adjustable power output,0-30 min timing,touch display,circulating water cooling,rod temperature overtemperature protection,temperature control mode and foot control,an MR compatible 2450 MHz microwave ablation apparatus is proposed.The microwave ablation apparatus can be placed in the magnetic resonance chamber without image artifact to perform the microwave ablation therapy while MRI scanning.(3)Firstly,the compatibility of the novel MR-compatible choke antenna was studied at 1.5 T,magnetically induced displacement force,MR image artifacts,and radiofrequency(RF)induced heating.Secondly,the magnetic resonance compatibility of the microwave ablation apparatus was also verified at 1.5 T.Then,to verify the compatibility of the 2450 MHz microwave ablation system and the ablation zones generated by the antenna under different microwave dose control,the MR-guided MWA was performed on fresh porcine livers at 1.5 T.Finally,the MR-compatible 2450 MHz microwave ablation system was successfully used for MR-guided rabbit liver ablation.The results show that the designed MR-compatible 2450 MHz microwave ablation system can achieve the compatibility with MRI system.The ablation can be accompanied by real-time imaging with interference.The design scheme combining the zirconia tip and titanium alloy tube not only makes the antenna eliminate the "tail"along the antenna shaft and generate nearly spherical ablation zones but also makes the antenna have excellent mechanical properties for clinical percutaneous intervention.Moreover,the compatibility between the antenna and the MRI system is realized.The antenna almost doesn’t produce magnetic displacement and RF heating at 1.5 T.The image artifacts produced by the antenna are uniform and visible.In conclusion,the designed MR-compatible 2450 MHz microwave ablation system is expected to be used in MR-guided interventional MWA for tumors,which is conducive to realizing accurate conformal ablation. |
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