Design and Realization of a Multi-Coil Array for B0 Field Control in a Compact 1.5T Head-Only MRI Scanner

Purpose: To design and implement a multi-coil (MC) array for B-0 field generation for image encoding and simultaneous advanced shimming in a novel 1.5T head-only MRI scanner. Methods: A 31-channel MC array was designed following the unique constraints of this scanner design: The vertically oriented magnet is very short, stopping shortly above the shoulders of a sitting subject, and includes a window for the subject to see through. Key characteristics of the MC hardware, the B-0 field generation capabilities, and thermal behavior, were optimized in simulations prior to its construction. The unit was characterized via bench testing. B-0 field generation capabilitieswere validated on a human 4TMRscanner by analysis of experimental B-0 fields and by comparing images for severalMRI sequences acquired with theMC array to those acquired with the system's linear gradients. Results: The MC system was designed to produce a multitude of linear and nonlinear magnetic fields including linear gradients of up to 10 kHz/cm (23.5 mT/m) with MC currents of 5 A per channel. With water cooling it can be driven with a duty cycle of up to 74% and ramp times of 500 mu s. MR imaging experiments encoded with the developed multi-coil hardware were largely artifact-free; residual imperfections were predictable, and correctable. Conclusion: The presented compact multi-coil array is capable of generating image encoding fields with amplitudes and quality comparable to clinical systems at very high duty cycles, while additionally enabling high-order B-0 shimming capabilities and the potential for nonlinear encoding fields.