Off‐resonance proton T1p dispersion imaging of 17O‐enriched tissue phantoms

Abstract

Proton T_1p dispersion imaging is a recently described method for indirect detection of ¹⁷O. However, clinical implementation of this technique is hindered by the requirement for a high-amplitude spin-locking field (γB₁ > 1 kHz) that exceeds current limitations in specific absorption rate (SAR). Here, a strategy is offered for circumventing high SAR in T_1p dispersion imaging of ¹⁷O through the use of low-amplitude off-resonance spin-locking pulses (γB₁ < 300 Hz). Proton spin-lattice relaxation times in the off-resonance rotating frame were measured in H₂¹⁷O-enriched tissue phantoms. On- and off-resonance T_1p 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 ¹⁷O-based image contrast. Magnetization transfer effects did not depend on ¹⁷O concentration and had no effect on image contrast. In conclusion, off-resonance proton T_1p dispersion imaging shows promise as a safe, sensitive technique for generating ¹⁷O-based T_1p contrast without exceeding SAR limitations.