Magnetic Resonance Systems Development for Point-of-Care MRI Platforms
Abstract
Magnetic resonance imaging utilizes electromagnets to produce anatomical images in both clinical and research settings. In the race towards increasing performance head-optimized scanners have begun playing a significant role in providing high quality imaging of the head. However, they are implemented using smaller geometries and as such fail to allow entrance of the patient past their shoulders. This is overcome by designing asymmetric gradient coils which have their imaging region located towards one end of the gradient coil, as opposed to the geometric center, allowing brain imaging. There exists interest in compact configurations which allow imaging further into the cervical spine which is unfeasible using current asymmetric gradients. This work seeks to explore the design of asymmetric gradient coils with shoulder cut-outs to enable neck imaging by allowing the patient to enter further into the gradient coil while maintaining the small inner radius of a head-only platform.
First, the relative trade-offs in designing an asymmetric shoulder cut-out gradient coil are explored and extended by rotating the transverse gradient axes to produce gradient coils which compensate for some of the electromagnetic burden due to the loss of conducting surfaces on the sides. Next, a complementary set of spherical harmonic active shims are designed and explored for implementation within this gradient coil configuration. From there the design of a cylindrical radiofrequency coil using gradient design techniques is investigated as preliminary work towards implementing these low-frequency design techniques which have had success designing gradient coils towards the design of radiofrequency coils.
Finally, motivated by the complexity of the induced eddy currents in the surrounding conductive structures due to asymmetric gradient coils the final project explores the design of a multi-coil matrix array aimed at fitting within the compact gradient housing to dynamically compensate eddy currents during imaging.
This work ultimately demonstrates the feasibility of implementing an asymmetric shoulder cut-out gradient coil with rotated transverse gradient axes to enable neck imaging in a compact MRI scanner while providing potential solutions to handle the increased eddy current complexity associated with a setup such as this.