Quantitative T1 and Effective Proton Density (PD*) mapping in children and adults at 7T from an MP2RAGE sequence optimised for uniform T1-weighted (UNI) and FLuid And White matter Suppression (FLAWS) contrasts

Quantitative T₁ and PD mapping is important for non-invasive tissue characterisation. Here, we aimed to calculate effective proton density (PD*) and quantitative T₁ relaxation maps at 7T using the MP2RAGE sequence and an analytical formula. This was applied to a short repetition time (TR_MP2RAGE) protocol developed to produce both Fluid And White Matter Suppression (FLAWS) and T₁-weighted uniform image (UNI) images. T₁ and PD* were estimated from analytical MP2RAGE signal equations for partial Fourier acquisitions. The sensitivity with respect to the TR_MP2RAGE and B₁ ⁺ effects on both excitation flip angles and inversion efficiency was evaluated. T₁ and PD* alteration with age (10-54 years) were evaluated at the shortest TR_MP2RAGE (4000 ms) in white matter (WM), cortical and deep grey matter regions. The T₁ values were insensitive to the choice of different TR_MP2RAGE. T₁ values varied over development into adulthood, especially for the deep grey matter regions whereas only a very small difference was observed for WM T₁. Effective PD maps were produced which did not show a significant difference between children and adults for the age range included. PD* maps and high precision T₁ maps were produced at 7T with 0.65 mm resolution in 7:18 min:s from an MP2RAGE protocol, previously optimised for UNI and FLAWS-related contrasts by incorporating the excitation flip angle and inversion efficiency B₁ ⁺ effects into the fit. Average WM T₁ values of adults and children were very similar (1092 vs. 1117 ms) while expected reductions in T₁ with age were found in deep GM.