Fig. 6
Schematic overview of the spin-locking mechanism. (1 + 2) A 90º RF pulse tips Mz into the transverse plane, creating Mxy. (3) Directly afterwards, a continuous RF pulse is applied (nearly) parallel to Mxy, creating the effective spin-lock field (Beff) (4). Mxy will now start rotating around Beff in a narrow cone and is therefore ‘locked’. Instead of normal T1 and T2 relaxation, Mxy will undergo T1-rho relaxation. (5 + 6) A -90º ‘tip-up’ RF pulse tips the remaining Mxy back towards the longitudinal axis, where the magnetization is stored again as Mz. The light gray arrows indicate a rotating frame of reference rotating with the Larmor frequency (ω0). Note that images 3 + 4 have been slightly enlarged for improved visualization