Research Of MR Multi-band Pulse Optimization And Ultra Low Field MRI Control System

As a non-invasive detecting technique,both magnetic resonance spectroscopy(MRS)and magnetic resonance imaging(MRI)play an important role in analytical chemistry,molecular physics,medical imaging,etc.Pulse sequences are utilized to accurately manipulate the spin system,and thus the expected signal can be obtained.Therefore,the design of pulse sequence is a hotspot in the magnetic resonance research field.In this thesis,a multi-band radio frequency(RF)pulse optimization algorithm for simultaneous multislice imaging was firstly proposed.Then,a pulse sequence control platform for the ultra-low field MRI system was detailed expatiated.Firstly,the optimal control theory and several numerical optimization algorithms of RF pulses in the magnetic resonance was reviewed.Then,the bandwidth pulse optimization for one spin system was proposed.By extending the above algorithm,we proposed a multi-band RF pulse optimization approach,and the performance was verified by both theoretical calculation and phantom imaging simulation.The results indicate that the optimized pulse can achieve the specific selective excitation with arbitrary thickness,distance and number of slices cooperating with the slice selection gradient.Secondly,an ultra-low field magnetic resonance pulse sequence control platform based on superconducting quantum interferometer device(SQUID)is designed.The system was divided into the coil module,the timing control,signal acquisition module,the software control module,etc.The general architecture of the system and its corresponding sub module were firstly described.Then,a Lab VIEW based software control system was developed and fully tested.Finally,the ultra-low field NMR experiment demonstrates that the validity of the control system.