Study On Key Problem And Imaging Application Of Muti-channel Radio Frequency Coil In MRI

Magnetic resonance imaging(MRI)is one of the most rapidly developing ad-vanced medical imaging diagnostic techniques.It has the advantages of non-invasive,non-radiation,multi-parameter,high-resolution.As the core component of excita-tion/reception of magnetic resonance(MR)signals,the performance of the radio fre-quency(RF)system directly determines the detection capability of the required MR signals.It is the critical technical bottleneck in high-field MRI.It is crucial to affect the image quality,imaging capability,imaging speed of MRI.Multi-channel RF coils are the foundation and core component of RF transmit and receive systems.How to improve the ability of RF coil to detect signal is one of the research hotspots at present.The signal-to-noise ratio can be improved by using multi-channel coil technology.However,it will lead to the increase of design complexity and electromagnetic(EM)coupling,which restrict the sensitivity,imaging speed and qual-ity.In this dissertation,we focus on the key technology and imaging application of MR multi-channel RF coil,explore the interaction mechanism among EM field,coil struc-ture and circuit in EM numerical simulation.Establish the theoretical system of fast numerical simulation.The decoupling methods between the channels or frequeicies are studied.Develop special multi-channel RF coil and multi-nuclei RF coil and carry out relevant application research to realize high-sensitive detection and high-quality imag-ing of MR signal.The main works and contributions are as follows:1.A field-circuit co-simulation method based on the concept of linear system trans-fer function is proposed.Build the RF coils model only in 3D field and obtain the field transfer functions.The important process like tuning,matching,and optimization are completed in the RF circuit field,and the transfer function of each unit sub-network is calculated.Achieve the co-simulation analysis through network analysis and matrix op-erations.Compared with conventional simulation method,the efficiency is improved by 1-2 orders of magnitude.The simulation and experimental study of RF coil proved the efficiency and accuracy of co-simulation method.2.A ~1H/¹⁹F dual-tuned RF coil structure based on the induced current compensa-tion or elimination decoupled is proposed in this thesis.The coupling between channels is reduced,as well as between the different nucleis.The decoupling effect is verified by simulation and experiment,and the coupling is reduced to nearly 1/5 of the traditional decoupling method.This coil design solves the interference between different frequen-cies and coupling between adjacent channels,and provides a more flexible scheme for multi-frequency RF coil design.3.In view of the highly sensitive detection requirements of low natural abundance nuclei signals,this paper focus on the structural design of multi-tuned transceiver,the RF circuit,control strategies,decoupling approach.A multi-channel RF quadruple-nu-clear transceiver system capable of ~1H/¹⁹F/²³Na/³¹P imaging is proposed and investi-gated for large sample applications at 3T.Bench tests performance evaluations show the coil arrays are sufficiently matched,decoupled and detuned.A range of imaging tests are performed by using the developed specific quadruple-nuclear RF coil system.4.A 24-channel head and spine integrated receiver coil for pediatric MRI at 3T was designed and constructed.Improvement in SNR was clear in the central regions(about 40%)in the transverse plane and in the surface region(nearly 2-fold)using the pediatric coil compared with the commercial coil configuration.SNR improvement was at least 18%compared with the adult spine coil.Improvements were obvious in the brain(32%to 38%)in vivo studies.The designed RF coil has been applied in clinical domestic 3T MRI system,Conjunct with clinical protocols,high-sensitivity detection of MR signals,high SNR and high resolution imaging are successfully acquired.