Experimental Method Of High Intensity Focused Ultrasound Cavitation Detection Based On Magnetic Resonance Imaging

High intensity focused ultrasound,as a non-invasive technique for the treatment of deep tumors,has attracted more and more attention.As one of the important biological effect of ultrasound,Ultrasonic cavitation can effectively gather energy.With more and more attention to cavitation,the safety and reliability of the monitoring tool has become particularly important.At present the common methods include Ultrasound-guided HIFU and Magnetic Resonance Imaging guided HIFU.With the advantages of multi dimensional imaging,temperature imaging and tissue sensitivity,So MRgHIFU is a hot spot of research.The main purpose of this study is to distinguish thermal damage and cavitation damage by magnetic resonance imaging and image postprocessing.So we can achieve cavitation damage monitoring.The main experimental material in this study is porcine tissue.The main experimental equipment is Siemens TIM Trio 3T Human body magnetic resonance scanning system and Magnetic resonance compatible HIFU transducer produced by IMASONIC.The main work includes the following three parts:Firstly,discussing the effect of micro bubble concentration on T2*value and T2 value.Secondly,determine the conditions of porcine thermal damage and cavitation damage.According to different experimental parameters(Probe parameters used in the experiment,signal frequency,Signal amplitude;).To ensure the stability conditions required to produce different damage are determined.Then,use the Simulator HIFU to simulate the sound field.Provide experimental conditions for the follow-up of the magnetic resonance monitoring experiment.Thirdly,by different magnetic resonance sequences(GRE,SE,IR,rs-EPI.etc.)distinguish two types of damage from the collected images and the post processing results.For the purpuse to check the detection of cavitation damage.The results of this experiment mainly include:(1)The effect of the micro bubble concentration on the transverse relaxation time was verified.Due to the high magnetic field,the magnetic susceptibility is obvious.With the increase of microbubble concentration the decay of transverse ralaxation time is faster;(2)The parameters of different damage corresponding to two different types of probes are determined in this experiment.]MHz probe which generates heat damage to the power required for the 58w;The power required for cavitation damage is 162w;The electrical power required to generate heat damage by 0.8MHz probe is 68W;The electrical power required for cavitation damage is 204w;(3)According to the results of magnetic resonance,it is concluded that different sequences can produce different results for the two kinds of damage.Temperature variation results and T2*value obtained from GRE sequences and the change of the displacement before and after the damage of the rs-EPI sequence can be very good to distinguish between two kinds of damage.The results showed that the experimental method of high intensity focused ultrasound cavitation detection based on magnetic resonance imaging is feasible.This also provides a variety of ideas and potential for magnetic resonance monitoring HIFU cavitation effect.