Pushing contrast at low field with very high B1

Motivation: Inherently reduced SAR at low B0 fields opens the possibility for sequences employing high B1 to generate contrasts inaccessible on common systems. Goal(s): Explore generation of magnetization transfer (MT) and inhomogeneous MT (ihMT) contrast using high B1 sequences on low-field MRI system. Approach: A tuned resonator was used to enhance B1 fields locally within a 0.55T scanner. Rapid gradient-echo based MT/ihMT sequences were tested on ex-vivo lamb brain sample. Results: Achieved ~9-fold increase in B1, boosting observed MTR/ihMTR. Unexpectedly, RF pulses failed to function at high B1 due to Bloch-Siegert and spin-locking; new pulse designs for this regime will form future work. Impact: Using high B1 fields at low B0 enables contrasts that were previously off-limits due to safety constraints at high B0. To exploit these with clinical hardware we demonstrate a passive resonator that increases the B1 by a factor of 9.