Off-resonance proton T1ρ dispersion imaging of 17O-enriched tissue phantoms

Proton T-1 rho dispersion imaging is a recently described method for indirect detection of O-17. However, clinical implementation of this technique is hindered by the requirement for a high-amplitude spin-locking field (gamma B-1 > 1 kHz) that exceeds current limitations in specific absorption rate (SAR). Here, a strategy is offered for circumventing high SAR in T-1 rho dispersion imaging of O-17 through the use of-low-amplitude off-resonance spin-locking pulses (gamma B-1 < 300 Hz). Proton spin-lattice relaxation times in the off-resonance rotating frame were measured in H-2 O-17-enriched tissue phantoms. On-and off-resonance T-1 rho dispersion imaging was implemented at 2 T using a spin-locking preparatory pulse cluster appended to a standard spin-echo sequence. On-and off-resonance dispersion images exhibited similar O-17-based image contrast. Magnetization transfer effects did not depend on O-17 concentration and had no effect on image contrast. In conclusion, off-resonance proton T-1 rho dispersion imaging shows promise as a safe, sensitive technique for generating O-17-based T-1 rho contrast without exceeding SAR limitations.