Design Of An MRI Compatible Cryosurgery System And Its Experimental Study

Cryotherapy is a developing method for cancer which is a minimally invasive ablation technique to inactivate tumor cells and reduce tumor burden.Compared with traditional tumor therapy,cryosurgery has some unique advantages in principle,effect and cost.However,cryosurgery is now mostly not a routine treatment for cancer.The main reasons are as follows.First,it is difficult to evaluate the effect of cryosurgery accurately.Second,it is challenging to monitor cryosurgery accurately.Therefore,it is necessary to conduct in-depth theoretical and simulation studies of cryosurgery.The accurate numerical model plays an important role in guiding the design of cryoprobe and cryosurgery planning.At the same time,it is necessary to design and develop an MRI compatible cryoprobe in order to make use of one of the most flexible diagnostic imaging methods at present to monitor the process of cryosurgery and precisely implement cryosurgery.For all the reason above,firstly,an unsteady two-phase flow coupled biological tissue heat transfer model is proposed to simulate and analyze the dynamic changes of tissue temperature field in cryosurgery.Using this model,the synergistic effect of multiple cryoprobes is analyzed qualitatively and quantitatively based on numerical methods.The temperature distribution and change process of hypothermic injury were predicted.The importance of the heat transfer mechanism and flow characteristics of the probe in accurately predicting the cooling capacity of the cryoprobe in multiple probes cryosurgery was revealed.In addition,for the purpose of destroying the target tissues as much as possible and avoiding irreversible damage to the surrounding healthy tissues,an optimized two-phase flow model based method for evaluating the performance of multiple probes is proposed to improve the precise preoperative planning and process control of cryosurgery in cancer treatment.Secondly,this paper introduces an NMR compatible liquid nitrogen cryoprobe.3.0-T MRI confirmed that the Cryoprobe had a good MRI compatibility.The unsteady state two-phase flow heat transfer model is used to analyze the dynamic change of temperature field in the tissue.Several groups of experiments were carried out to evaluate the freezing effect of cryoprobe theoretically and experimentally.In order to optimize the effect of cryosurgery,the tumor cell killing experiment was carried out by adding ferric oxide nanoparticles,and the survival rate of tumor cells was analyzed.It was verified that with the help of nanoparticles,the MRI compatible cryoprobe could kill tumor cells effectively without harming the surrounding healthy tissues.Next,a thermal simulation rmodel of magnetic nanoparticles in the RF electric field of nuclear magnetic resonance(NMR)was established.Using this model,the radiofrequency heating of tissues with Fe3O4 nanoparticles under different electric field intensities in NMR imaging was studied.The time-varying curves of the volume of bread envelope with and without adding Fe3O4 nanoparticles under different electric field intensities were also compared.The results of this study can be used to evaluate the heat production of Fe3O4 nanoparticles in magnetic field,which results in the overall increase of tumor temperature and counteracts the cooling effect of some cold knives.The results of numerical simulation can guide the nano-cryosurgery in the radio frequency magnetic field of MRI,and improve the safety and effectiveness of the operation.Finally,the preoperative planning of cryosurgery is studied,and a new optimization method based on a multi-body motion for computerized planning of multi-probe is proposed.A three-dimensional two-phase flow model is used to evaluate the optimal layout of cryoprobes.Defect function was used to analyze cryoablation schemes for multiple liquid nitrogen cryoprobes with the same insertion depth.The simulation results show that the layout based on multi-body movement method can get the best freezing probe layout,which can produce the maximum freezing damage to the target tissue and bring the minimum damage to the adjacent healthy tissue.In summary,the coupling effect of multiple probes in cryosurgery is analyzed innovatively by using a two-phase flow coupled bio-heat transfer model.An NMR compatible cryoprobe system is designed and evaluated with magnetic nanoparticles assisted cryosurgery.Radiofrequency heating of tissues with Fe3O4 nanoparticles under different electric field intensities in magnetic resonance imaging during cryosurgery was studied.A new optimal computerized planning algorithm of multiple probes based on a multi-body motion is proposed.These findings could further advance the application of cryosurgery as a precise targeted minimally invasive approach to cancer therapy.