Development Of Vertebral Phased Array Coil In Low-field MRI System

Magnetic Resonance imaging (MRI) is one of the key tools in medical treatment and research, which has no invasion, ionization and radiation characteristic. RF (radio-frequency) coil is one of the important components of MRI system. Receiving coil has a very important influence on the image quality because it is placed at the start of the receiving chain. Multi-channel phased array coils have much higher SNR, higher spatial resolution, faster imaging speed compared with other kinds of coils. However the design of multi-channel phased array coil is generally aimed at super-conduct high-field system at present time[1]. In this paper, the design of a multi-channel phased array RF receiving coil based on the figure-eight surface coil structure is discussed and implemented specially for vertebral imaging in low-field MRI system. In addition, experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are presented.The main contents of the paper include:First, the theory of NMR ( nuclear magnetic resonance ) is introduced briefly, including the theory of NMR and MRI. The hardware structure of MRI scanner is described, which consists of magnet, spectrometer and computer subsystems.Second, the basis of RF coil is introduced, including tuning and matching interface, decoupling between receiving coil and transmitting coil, SNR (signal and noise ratio) of coil, types of coil, coil interface circuit and essential points of designing an RF coil.Third, the design of a two-channel RF receiving coil which is implemented specially for vertebral imaging in low-field MRI system is presented. The coupling of the two coils is resolved by adjusting the spatial location of the two coils, overlapping partially so that the coupling problem is minimized. The two-channel RF coil is integrated into the MRI scanner, and the experimental results obtained with both phantom and human vertebral images in a home-built 0.3T MRI system are given. The experiments proved that the two-channel RF coil has good isolation and good image quality. Moreover, a three-channel RF coil is designed and integrated into MRI scanner, and phantom as well as human vertebral experiment is also performed.