ABSTRACT
PURPOSE: Delta relaxation-enhanced MR (dreMR) is a field-cycling quantitative method for molecular imaging. The dreMR method uses a B0 insert coil to shift the magnitude of the main magnetic field as a magnetization preparation phase of the pulse sequence. Here, an improved coil design method is presented that minimizes field inhomogeneities and allows for explicit control of the ROI. METHODS: A solenoid produces the bulk field shift, and a boundary element method is employed to design in-series shim and shield layers. A design is presented and compared to the current generation dreMR coil design on field inhomogeneity maps, shield performance, and simulated dreMR image. A proof-of-concept design is also presented with an ROI shifted from isocenter. RESULTS: The new design is able to image a sphere of 8.5 cm in diameter with field inhomogeneity of < 1% versus the previous design's 5 cm. The new design presented an increase in shielding capabilities, whereas inductance and resistance increased. For a simulated dreMR image, the new design presented errors < 10% compared to an ideal field simulation, whereas the previous design had errors > 18%. The shifted ROI design produced a region of < 1% inhomogeneity much larger than a design with no shim layer. CONCLUSION: The new design method was found to greatly improve the insert coil field homogeneity and reduce errors in dreMR imaging in simulation without detriment to shielding. This method's capability to increase ROI and control its location will be used to design human dreMR coils going forward.
