iDQC MR Imaging with Contrast of Off-resonance Rotating-frame Spin-Lattice Relaxation

Methods In Fig. 1, the low-power rf pulse (ω1)y and frequency offset ∆ω constitute an effective spin-locking field along the z′ axis of a tilted rotating frame, with an effective frequency 2 2 1 ( ) e ω ω ω = + ∆ and a tilt angle θ = arctan(ω1/∆ω) with respect to the normal Larmor rotating frame (θ = π/2 for an on-resonance spin-locking pulse without frequency offset) [1,2]. The magnetization aligned along the effective field ωe relaxes with a relaxation time constant during the locking period TSL. For iDQCs, the final observable transverse magnetization becomes [3]