Design and study of high sensitivity RF coil in NMR imaging system

Abstract

High sensitivity and good homogeneity are two major importance in RF coil design. Emphasis, however, should be placed on the improvement of sensitivity since it determines the signal-to-noise ratio which ultimately affects the resolution of image and imaging time. Homogeneity is mainly related to the image distortion and it is determined by the shapes and sizes of coil employed. In order to improve the sensitivity of the NMR RF coil, the parameters determing the signal-to-noise ratio of RF coil are analyzed. Sensitivity improvement can be achieved by either increasing B1 field or decreasing resistance of the RF coil. Characteristics of copper foil and tube as conducting wire on a coil are studied in terms of skin effect at high frequency. It is also shown that balanced mode matching can be used for the sensitivity improvement by increase of number of turns in RF coil and achieved sensitivity gain experimentally observed reached as much as a factor two. This major sensitivity improvement is theoretically analyzed and experimented results are presented.