The Study Of The Application Of Magnetic Resonance Non-invasive Temperature Measurement To Microwave Ablation

Objective: Through magnetic resonance gradient echo sequence,this paper obtained phase change information caused by temperature variation during microwave ablation,calculated corresponding temperature variation,and compared with actual temperature variation measured by the optical fiber,so as to study the accuracy and feasibility of magnetic resonance noninvasive temperature measurement based on proton resonance frequency phase subtraction applied to MRI-guided microwave ablation,and the preliminarily correlation between pathological change and temperature after tissue ablation.Methods: Part I: Magnetic Shielding Modification of Microwave Ablation Instrument with Magnetic Compatibility By adding aluminum alloy outer cover and conjugate coil,this paper modified non-magnetic compatibility microwave ablation equipment into magnetic compatibility,magnetic resonance imaging scanning of microwave ablation process,carried out by using isolated bovine liver tissue,and observed interference of equipment on magnetic resonance signals.Part II: Agar Phantom Magnetic Resonance Temperature Measurement Experiment Firstly,use the agar phantom with the same temperature as the magnetic resonance room to carry out the temperature measurement experiment during the constant temperature process to evaluate the stability of the whole temperature measurement system.Secondly,heat the agar phantom by microwave ablation equipment,set up magnetic resonance scanning parameters and ablation parameters(power 30 w and 40 w,time5.0min),and acquire phase changes in the ablation process through gradient echo sequence in a 1.5T superconducting magnetic resonance system,and take actual temperature variations measured by an optical fiber probe as the standard value.Thus,magnetic resonance temperature measurement results and optical fiber temperature measurement results were compared and analyzed,and the precision of magnetic resonance non-invasive temperature measurement were evaluated.Part III: Isolated Pork Tissue’s Magnetic Resonance Temperature Measurement and Pathological Connection in Microwave Ablation Process Select the isolated pork tissue to be inserted the magnetic compatible microwave antenna and optical fiber at a certain distance,confirm the distribution of microwave antenna needle tip and optical fiber probe be satisfactory,and set up ablation parameters(power 40 w,50w and 60 w,time5.0min).The isolated pork microwave ablation heating temperature measurement experiment was carried out in a 1.5T superconducting magnetic resonance chamber system using gradient echo sequence.T1 FSE and T2 FSE scans were performed before starting microwave ablation and immediately after ablation to observe tissue signal variations,and pathological examination and its relation with temperature were performed after operation.The actual temperature variation measured by optical fiber probe as the standard value,the magnetic resonance temperature measurement results and optical fiber temperature measurement data are compared and analyzed to further verify the precision of magnetic resonance non-invasive temperature measurement.Results: Part I: The interference to magnetic resonance signals during microwave ablation was obviously improved by modifying the magnetic shielding.Part II: In the agar phantom,the maximum error between the magnetic resonance temperature measurement result and the standard value was 3.61℃,the minimum error was 0.01℃,and the average error was 1.19±0.78℃.Part III: In isolated pork tissue,the maximum error was 4.26℃,the minimum error was 0.05℃,and the average error was1.75±1.00℃.The coagulation necrosis area showed a low signal on T2 FSE after microwave ablation.There was no significant difference between T2 FSE low signal area and the measured 60℃ isotherm areaConclusions:1.The electromagnetic compatibility between microwave ablation and magnetic resonance can be improved by magnetic shielding modification of microwave ablation instrument with magnetic compatibility.2.Temperature measurement technology based on PRF phase method is precise in MRI-guided microwave ablation.3.T2 FSE low signal area after microwave ablation and the measured 60℃ isotherm area are consistent with the coagulation necrosis area,which can accurately determine the ablation boundary.