Incomplete Spoiling Correction for 3D T 1 Mapping

Assess the impact of incomplete spoiling and spatial saturation on $T_1$ mapping using the variable flip angle (VFA) spoiled gradient recalled echo sequence (SPGR). Develop a correction for incomplete spoiling that results in an accurate estimate of $T_1$ , essential for quantitative MRI applications.

A correction factor, derived from extended phase graph simulations, was applied to the measured SPGR signal to account for deviations from the theoretical steady-state signal. An iterative fitting process was used, refining the incomplete spoiling correction factor at each step based on the updated $T_1$ estimate. The incomplete spoiling correction method was validated against inversion recovery spin echo in phantom experiments and applied to in vivo data at 3T. Additionally, the hypothesis that spatial saturation disrupts the steady-state was also tested and validated in a phantom.

Without a correction, the median $T_1$ error was +7.4% (IQR [4.4, 9.6]%) in both simulations and phantom experiments. After applying the correction, the median $T_1$ error decreased to -0.3% (IQR [-2.5, 2.1]%). In vivo, incomplete spoiling caused $T_1$ overestimation of 10-50 ms depending on $B_1^{+}$ inhomogeneity. Spatial saturation induced on average a -10% $T_1$ bias.

A correction for incomplete spoiling is essential to achieve an accurate measure of $T_1$ using the VFA SPGR method, addressing systematic $T_1$ overestimation when using this $T_1$ mapping technique. Furthermore, other mechanisms that may disrupt the steady-state signal, such as spatial saturation, should be considered.