Accurate T1 mapping of short T2 tissues using a three-dimensional ultrashort echo time cones actual flip angle imaging-variable repetition time (3D UTE-Cones AFI-VTR) method

PurposeTo develop an accurate T-1 measurement method for short T-2 tissues using a combination of a 3-dimensional ultrashort echo time cones actual flip angle imaging technique and a variable repetition time technique (3D UTE-Cones AFI-VTR) on a clinical 3T scanner. MethodsFirst, the longitudinal magnetization mapping function of the excitation pulse was obtained with the 3D UTE-Cones AFI method, which provided information about excitation efficiency and B-1 inhomogeneity. Then, the derived mapping function was substituted into the VTR fitting to generate accurate T-1 maps. Numerical simulation and phantom studies were carried out to compare the AFI-VTR method with a B-1-uncorrected VTR method, a B-1-uncorrected variable flip angle (VFA) method, and a B-1-corrected VFA method. Finally, the 3D UTE-Cones AFI-VTR method was applied to bovine bone samples (N=6) and healthy volunteers (N=3) to quantify the T-1 of cortical bone. ResultsNumerical simulation and phantom studies showed that the 3D UTE-Cones AFI-VTR technique provides more accurate measurement of the T-1 of short T-2 tissues than the B-1-uncorrected VTR and VFA methods or the B-1-corrected VFA method. The proposed 3D UTE-Cones AFI-VTR method showed a mean T-1 of 24025 ms for bovine cortical bone and 218 +/- 10 ms for the tibial midshaft of human volunteers, respectively, at 3T. ConclusionThe 3D UTE-Cones AFI-VTR method can provide accurate T-1 measurements of short T-2 tissues such as cortical bone. Magn Reson Med 80:598-608, 2018. (c) 2018 International Society for Magnetic Resonance in Medicine.