Accuracy of T1 and equilibrium magnetization maps using a spoiled gradient-recalled echo sequence with variable flip angles at 4.7 T, 7 T, and 9.4 T: A gadolinium-doped gel phantom study

INTRODUCTION A T1map is required for some quantitative MR imaging applications. In dynamic contrast-enhanced (DCE) MRI, a T1map obtained before contrast agent administration allows us to convert image intensity into gadolinium concentration. Spoiled gradientrecalled echo (SPGR) sequence with variable flip angle (VFA) method has been widely used to construct T1map. However, in our mouse DCE-MRI experiments at 9.4 T, we observed shorter T1 values in gadolinium-doped agar gel phantoms alongside the animal from the SPGR-VFA approach compared to the corresponding T1s measured separately by inversion recovery (IR) 1D NMR spectroscopy. Thus, we investigated the T1map accuracy of the SPGR-VFA approach. Because the 9.4 T is classified as high field in MR and T1 has magnetic field dependence, the examination was also carried out at 4.7 and 7 T using the same set of the phantoms. In addition to T1map, an equilibrium magnetization (Mo) map, which could be obtained together with T1map calculation, is also used to quantify the gadolinium concentration in DCE-MRI. Therefore, Momap accuracy was also examined.