Research On Eddy Current In Magnetic Resonance Imaging And Correction Of Image Artifacts

MRI(Magnetic Resonance Imaging,MRI)is a very advanced medical imaging technology.It has gradually been accepted by people and becomes a common diagnostic method because of its advantages of being distinct and convenient,harmless to the human body,etc.The equipment of MRI is becoming universal in hospitals.But there is a serious problem in the permanent magnet magnetic resonance,the eddy current induced in the metal parts around the gradient coil in the process of MRI by working current due to the complex internal structure of the system,the existence of the eddy current can generate distortion in the waveform of the gradient field and restrict the imaging speed of magnetic resonance imaging at the same time.What’s worse is that eddy current will shift the odd and even echoes in the echo planar imaging(EPI)sequence and affect the quality of images and produce N/2 artifacts in the reconstructed images eventually.This paper can be divided into two main parts,the first part is about the eddy current problems in the permanent magnet MRI.A method of measuring the magnet eddy current field is presented.Combined with the law of electromagnetic induction,we make a magnet eddy field measuring device so as to measure the electromotive force in the coils induced by the ideal magnetic field and the actual magnetic field,after that get the ideal magnetic field and practical field after mathematical calculation.After then,the hardware acquisition and the software processing methods are used to subtract the ideal gradient field and the practical gradient field.The waveform is presented in real time so as to realize the measurement of the eddy current field.The second part is about the N/2 artifact problem in the permanent magnet magnetic resonance images caused by eddy current and some other factors,an image post-processing program compiled in the C#language programming environment is presented,using the phase correction method to eliminate the shift and phase difference between the odd and even lines data of echo planar imaging(EPI).After processing some actual magnetic resonance image data the N/2 artifacts in the original image have been corrected.