Universal versus subject-specific parallel transmit pulses for inhomogeneous magnetization transfer at 7T

Motivation: B1+ inhomogeneity at 7T renders uniform magnetization transfer (MT) and inhomogeneous MT (ihMT) difficult. B1+ and saturation inhomogeneity can be significantly reduced using parallel transmission (pTx) technology and RF pulse design, as shown in previous applications in chemical exchange saturation transfer (CEST) and MT. Goal(s): To evaluate the performance of subject-specific and universal pre-saturation pTx pulse design in MT and ihMT at 7T. Approach: Used PASTEUR framework to explore pre-saturation pTx pulse design for single and dual off-resonance pre-saturation. Results: 7T subject-specific and universal pTx pulses improved saturation homogeneity and reduced image non-uniformity in simulated ihMTR and MTR. Impact: To enable high-resolution whole-brain ihMT imaging at 7T, we require dual and single off-resonance pulses that produce a spatially uniform saturation. Our simulations showed improved ihMT uniformity using subject-specific and universal pre-saturation pTx pulses to a range comparable to 3T.