A gradient and RF system for open access low field MRI
This thesis describes work carried out to improve the operation of a 0.01 T open access low field MRI system. Two planar surface gradient coil sets and a new three channel gradient amplifier were designed, constructed and tested. Surface transmit coils and surface receive coils and a balanced preamplifier were developed to allow RF pulse generation and signal detection without compromising the single-sided access of the system. The properties of litz wire were investigated by simulation and testing, and it was shown and the established litz wire theory can also be applied to the design of cooled coils. Images were obtained to show the operation of the new gradient amplifier and to demonstrate the combined operation of a surface gradient coil, surface receive coil, surface transmit coil and the low noise preamplifier. A large surface receive coil was used to acquire in vivo images for the first time of surface regions of a volunteer's head. Images obtained with a cryogenic receive coil, showed an SNR improvement relative to a room temperature coil in agreement with theoretical predictions.