A General T1ρ Relaxation Model for Spin-Lock MRI using a Rotary Echo Pulse

Jing Yuan¹, Yi-Xiang Wang¹

T1 relaxation was conventionally described to follow a purely monoexponential decay as a function of the spin lock time. However, the validity of this monoexponential decay may be violated in the presence of field inhomogeneities, especially at extremely low spin lock frequencies. T1 relaxation behavior using a rotary echo spin lock pulse was studied using the Bloch Equation and the rotation matrix transformation. A general analytical expression was derived to describe the T1 relaxation at different spin lock frequencies in the presence of B0 inhomogeneity, and verified experimentally by phantom and in vivo imaging from 50Hz to 500Hz.