Research On Magnetic Resonance Thermometry Based On The Phase Difference Model Of Water-fat Separation And Self-reference

With the factor that MR devices can provide the near real-time tomography images of the organization and temperature in hyperthermia process,the noninvasive hyperthermia surgery of MRI-guided high-intensity focused ultrasound is playing an important role of cancer treatments.At present,magnetic resonance technology can provide a good image of human tissue,but it needs to be improved in the realization of accurate temperature measurement and high spatial and temporal resolution.Among all kinds of magnetic resonance thermometry,the proton resonance frequency(PRF)method is the most widely used.Not simple in practice,however,this method is easy to be affected by the magnetic field drift of the MR instrument,the motion of the measured object and the effect of the lipid protons.This paper proposes a new method of PRF based on the self reference phase difference model of water and fat separation to solve the problem of the temperature measurement of the PRF method.Firstly,it is analyzed that the magnetic resonance imaging technique is used to measure the spatial temperature information of the body,and the method of thermomrtry with the proton resonance frequency is introduced.Aiming at the measuring error caused by the drift of the main magnetic field and the motion of the measured object,it is used that the temperature measurement model of the self-reference phase to correct the error.The model,taking into account the influence of the main magnetic field intensity and the inter frame motion,compute the object pixel phase of non-heating zone which is used to the generate plane fitting as the reference phase target PRF phase subtraction thermometry in the real time frame image.The computation reference phase is only related to the real time frame information,therefore,it can eliminate the influence of time varying interference factors such as inter frame motion and magnetic field variation.In view of the temperature measurement error caused by the temperature insensitive of the lipid proton,the water fat separation model is introduced to obtain the water proton phase with a linear relationship of temperature.The water proton phase model obtained include the water proton phase of reference area which be used to fit the last reference phase plane of the target area,and the water proton phase of target area which subtract the final phase reference to calculate temperature.In order to save the time of data collection and parameter calculation of water and fat separation,the threshold value of the phase change of the reference area is proposed as a criterion for the separation and renewal information of water and fat.According that the complex operation of MR temperature data leads to truncation phase,the process of finding the real phase from the detection phase is decomposed into the quested real phase of the spatial domain and the time domain.Correspondingly,the phase unwrapping model based on fuzzy quality map is used to solve the static phase in the space domain,and the phase unwrapping algorithm based on the temperature phase relation is used to calculate the time domain phase.In order to evaluate the effect of the new model,the Bstar 150 superconducting magnetic resonance instrument is used to measure the temperature of different ratio water and fat of phantom,Compared with the results of Fiber optic temperature measurement,the maximum temperature error between the measurement results and Fiber optic temperature measurement is 1.12 ?.Temperature singularity haven't showed the experiment results.The paper has made preliminary technical preparations to further work about MRI applied hyperthermia.