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

Purpose To 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. Methods First, 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. Results Numerical 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 240 ± 25 ms for bovine cortical bone and 218 ± 10 ms for the tibial midshaft of human volunteers, respectively, at 3 T. Conclusion The 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.