Research On Gradient Eddy Current Compensation Based On Pick-up Coil Method

MRI(Magnetic Resonance Imaging)is one of the most advanced tools in modern medical imaging diagnosis.The main magenetic field,the gradient field and the radio frequence field combined together make MRI a reality.The gradient field can locate the MR(Magnetic Resonance)signal in space.And the gradient field is generated by applying current to the gradient coil.Eddy current would be generated by the metal compoents around the outside of the gradient coils to resist the rapidly changing of the current applied to the gradient coil.As a result,the accuracy of the spatial positioning of the MR signal and the quality of the MR imagine will be reduced.The research on eddy current compensation means a lot to MRI.In this paper,the PCB(Printed Circuit Board)technology is used to produce the planar pick-up coil circuit and tooling.An experimental system for eddy current compensation based on the pick-up coil method is established.The hardware and the software of the system are established.And the feasibility of the system is verified by the eddy current compensation experiment.The main works are as follows:1.The design of the eddy current compensation system is Completed.The key module is established based on the PXIe-7992 FPGA module,NI-4751 and NI-5783 boards.Using differential lines to transmit signals,completing the Wiring plan of the system.VI(Visual Instrument)generating the gradient waveform is programmed.And VI used to process the received signals is also programmed.2.Design of planar pick-up coil circuit and structural tooling.According to the assembly of the gradient coil,we take the advantage of th PCB technology to design our planar pick-up coil circuit.And we use it on the eddy curmt compensation expirement.The planar pick-up coil has accurate and controllable coil parameters,which is exactly what the traditional pick-up coils doesn't have.Combine with the tool,the stability of the planar pick-up coil circuit will be improved.As a result,the accuracy of the signal receiving will be improved too.3.Eddy current compensation experiment.Eddy current compensation is an important process to eliminate the influence of eddy current on the gradient magnetic field.The key to the experiment is the accuracy of the acquisition of the induction signal generated by the planar pick-up coil which is set in the changing gradient field.The result of the expirement shows that the eddy current compensation system based on planar pick-up coil circuit can work well.