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

PURPOSE

To develop an improved T prepared (T prep) balanced steady-state free-precession (bSSFP) sequence and signal relaxation curve fitting method for myocardial T mapping.

METHODS

Myocardial T mapping is commonly performed by acquisition of multiple T prep bSSFP images and estimating the voxel-wise T 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 T prep RF pulses, which may decrease the robustness of T mapping. Therefore, we propose a novel T mapping sequence that incorporates an additional image acquired with saturation preparation, simulating a very long T prep echo time. This enables the robust estimation of T maps using a 3-parameter fit model, which captures the effect of imaging pulses and other imperfections. Phantom imaging is performed to compare the T 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 T values generated by the proposed 3-parameter model fitting do not change with different choices of the T prep echo times, and are not statistically different than the reference values for the phantom (P = 0.10 with three T prep echoes). The two-parameter model exhibits dependence on the choice of T prep echo times and are significantly different than the reference values (P = 0.01 with three T prep echoes).

CONCLUSION

The proposed imaging sequence in combination with a three-parameter model allows accurate measurement of myocardial T values, which is independent of number and duration of T prep echo times. Magn Reson Med 74:93-105, 2015. © 2014 Wiley Periodicals, Inc.