Sensitivity and spatial selectivity of transverse field RF surface coils: A theoretical and experimental study at 2.35T

A number of clinical magnetic resonance imaging/spectroscopy applications require a careful selection of the radiofrequency (RF) coil design to optimize the coil sensitivity and spatial selectivity in a well-defined region of interest. Small surface receiver RF coils are often used because they are highly sensitive, easy to construct, and provide spatial signal localization. We have analysed axial (square loop, SL) and transverse (figure-of-eight, FO8; butterfly, BC) RF field surface coils to study sensitivity and spatial selectivity along the coil axis. We have performed simulations with a finite element method at 100MHz, and built prototypes of the coils. GE images were acquired in the presence of an oil phantom using a 2.35T Bruker animal scanner. The results show a higher sensitivity and a more pronounced spatial selectivity along the coil axis with the transverse coils, as compared to the standard SL in the proximity of the RF coil plane. Moreover, a transmit flip angle calibration has been performed and a pronounced gain is obtained with the transverse coils. These features should be useful to optimize the RF coil sensitivity and spatial selectivity in a specific region of interest along the coil axis.