UC San Diego

Purpose

To develop an accurate T₁ measurement method for short T₂ 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 B₁ inhomogeneity. Then, the derived mapping function was substituted into the VTR fitting to generate accurate T₁ maps. Numerical simulation and phantom studies were carried out to compare the AFI-VTR method with a B₁ -uncorrected VTR method, a B₁ -uncorrected variable flip angle (VFA) method, and a B₁ -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 T₁ of cortical bone.

Results

Numerical simulation and phantom studies showed that the 3D UTE-Cones AFI-VTR technique provides more accurate measurement of the T₁ of short T₂ tissues than the B₁ -uncorrected VTR and VFA methods or the B₁ -corrected VFA method. The proposed 3D UTE-Cones AFI-VTR method showed a mean T₁ 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 T₁ measurements of short T₂ tissues such as cortical bone. Magn Reson Med 80:598-608, 2018. © 2018 International Society for Magnetic Resonance in Medicine.