Improved quantitative myocardial T2 mapping: Impact of the fitting model.

PURPOSE To develop an improved T2 prepared (T2 prep) balanced steady-state free-precession (bSSFP) sequence and signal relaxation curve fitting method for myocardial T2 mapping. METHODS Myocardial T2 mapping is commonly performed by acquisition of multiple T2 prep bSSFP images and estimating the voxel-wise T2 values using a two-parameter fit for relaxation. However, a two-parameter fit model does not take into account the effect of imaging pulses in a bSSFP sequence or other imperfections in T2 prep RF pulses, which may decrease the robustness of T2 mapping. Therefore, we propose a novel T2 mapping sequence that incorporates an additional image acquired with saturation preparation, simulating a very long T2 prep echo time. This enables the robust estimation of T2 maps using a 3-parameter fit model, which captures the effect of imaging pulses and other imperfections. Phantom imaging is performed to compare the T2 maps generated using the proposed 3-parameter model with the conventional two-parameter model, as well as a spin echo reference. In vivo imaging is performed on eight healthy subjects to compare the different fitting models. RESULTS Phantom and in vivo data show that the T2 values generated by the proposed 3-parameter model fitting do not change with different choices of the T2 prep echo times, and are not statistically different than the reference values for the phantom (P = 0.10 with three T2 prep echoes). The two-parameter model exhibits dependence on the choice of T2 prep echo times and are significantly different than the reference values (P = 0.01 with three T2 prep echoes). CONCLUSION The proposed imaging sequence in combination with a three-parameter model allows accurate measurement of myocardial T2 values, which is independent of number and duration of T2 prep echo times. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.