Design of Rotated Surface Coil Array for Multiple-Subject Imaging at 400 MHz

Multiple-subject magnetic resonance imaging has been used in phenotyping studies to reduce the total experimental time by simultaneously capturing images of multiple animals using single or multiple radio frequency (RF) coils. However, conventional methods must consider decoupling circuits to minimize the mutual inductance coupling between RF coils. These decoupling circuits unnecessarily increase the field of view and image acquisition times. In this study, we propose a rotated surface (RS) coil that can generate a uniformly transmitted magnetic field (
$\vert \text{B}_{1}^{+}\vert $
) and minimize the distance between coils when used for multiple-animal imaging without decoupling circuits. The RS coil was designed using an electromagnetic (EM) simulation software, and the rotation angle, which creates a uniform
$\vert \text{B}_{1}^{+}\vert $
-component, was derived by mathematical calculations. We compared the
$\vert \text{B}_{1}^{+}\vert $
-component uniformity produced by RS coils with different rotation angles and a 4-leg high-pass filter birdcage coil in multiple-coil arrays at the same location using EM simulations. The RS coil displayed a uniformity greater than 94% and 84% uniformity when used as a single-channel and multiple-coil array in the central axial plane, respectively. Following the EM simulations, a multiple-mice RS coil array was manufactured, and a bench test was performed to ensure its operation at 400 MHz and for coupling analysis. T
₁
-FLASH images of the four phantoms and mice were acquired using a multiple RS coil array in a 9.4-T preclinical MR system. The signal-to-noise ratio and uniformity were measured using the phantom images.