Development and Characterization of An Unshielded PatLoc Gradient Coil for Human Head Imaging

A cylindrical head gradient insert for human imaging with non-linear spatial encoding magnetic fields (SEMs) has been designed, optimized and successfully integrated with a modified 3T clinical MR system. This PatLoc (parallel acquisition technique using localized gradients) SEM coil uses SEMs that resemble second-order magnetic shim fields, but with much higher amplitude as well as the possibility for rapid switching. This work describes the optimization of a coil design and measurement methods to characterize its SEMs, induced self-eddy currents and concomitant fields. Magnetic field maps of the SEMs are measured and it is demonstrated that the induced self-eddy current magnetic fields are small and can be compensated. A method to measure concomitant fields is presented and those fields are compared to simulated data. Finally, in vivo human images acquired using the PatLoc system are presented and discussed.