Research And Design Of ¹H/³¹P/²³Na MRI Coil

Magnetic Resonance Imaging(MRI)is a widely used non-invasive imaging method that provides a variety of high-resolution soft tissue comparisons and multiple functional information,and MRI has become a very useful tool in clinical care.Modern MRI technology is mainly 1H imaging,and its development focuses on maximizing signal to noise ratio(SNR),achieving the best possible tissue contrast and improving image quality.High field strength lays the foundation for high SNR,improving inter-tissue contrast and inhibiting motion and weakening vortex flow can improve image quality,but these require a good RF coil to obtain the MR signal to achieve a more significant gain effect.With the development of high-field MRI system technology,the nuclide used for imaging are no longer limited to 1H,for MRI using nuclei outside of 1H is also useful.31P plays an important role in energy metabolism and has certain value in the auxiliary diagnosis of ischemic heart disease,atherosclerosis and dermatomyositis.Magnetic resonance imaging at 23Na is considered an important addition to 1H MRI to detect a variety of physiological diseases like tumors,cartilage health,kidney failure,and thus requires research on the 31P/23Na imaging coils.However,detectio of 31P/23Na remains challenging with a signal intensity of 4?5 orders of magnitude weaker than 1H,so 1H imaging coils are still required for localization and uniform field to develop ¹H/³¹P/²³Na RF coils.This only avoids the movement of the scan position caused by replacing the coil,but also reduces the imaging time to reduce the patient discomfort.This thesis studies the mul-nuclei imaging coil technique for the research needs of the ¹H/³¹P/²³Na imaging coil.The main contents of the paper are as follows:(1)The overall design of different types of RF coils is introduced and surface coils were made in theory to obtain imaging data.Theoretical analysis and simulation of bird cage coil are conducted to verify the magnetic field distribution in homogeneous mode.The frequencies of the different resonant modes are optimized by the regulation of the coil physical structure,reducing the coupling action between the different coils.Finally,the saddle coil was simulated and analyzed for the RF field uniformity to obtain the imaging space size.(2)In view of the problem of many complex parameters of bird cage coil structure,an imaging bird cage coil capacitor calculation software was developed based on the Qt platform,which can estimate the coil tuning capacitor range before the electromagnetic simulation and solve the problem of slow simulation speed caused by the complex bird cage coil simulation model.The model improves the coil matching circuit and verifies the results after parameter scanning,which accelerates the simulation speed and optimizes the simulation accuracy.(3)The coil design structure is developed by comparing the existing double resonant coil design scheme,through preliminary electromagnetic simulation evaluation and then actual production.The coil consists of shielding layer,Four-ring bird cage coil(1H/31P transmit and receive)and saddle type coil(23Na transmit and receive).Complete the commissioning of machining coil support assembly and coil circuit,and test the electrical indicators of coil performance to meet the imaging conditions.At last,the experiments were carried out on the 4.7T MRI system with the self-developed multi-nuclear MRI console,and obtained the desired images,verified the feasibility of the ¹H/³¹P/²³Na coil design scheme,provided a new design scheme for three nuclear MRI coil.