Quadruple-refocused spin-locking: a robust method for high amplitude T1ρ imaging

Motivation: T1ρ relaxation mechanism during spin-locking is widely used for monitoring macromolecular remodeling, such as early-stage osteoarthritis. However, T1ρ measurements are sensitive to B0 and B1 magnetic field inhomogeneities. Goal(s): To reduce artifacts in spin-locking and therefore to promote its potential for more application scenarios. Approach: With paired 180° pulses and based on the principle of rotary-echo to reduce artifacts, we applied numerical simulation and experiments to validate our proposed module and compare it with three existing preparation modules. Results: Among the four modules, quadruple-refocusing shows the highest performance in compensating for artificially induced B0 and B1 field inhomogeneities. Impact: With quadruple-refocusing, high amplitude spin-locking can be improved in the compensation of field inhomogeneities. The presented method has potential application in the T1ρ quantification in low-field MRI.