Improved quantitative myocardial T2 mapping: Impact of the fitting model

PurposeTo develop an improved T-2 prepared (T(2)prep) balanced steady-state free-precession (bSSFP) sequence and signal relaxation curve fitting method for myocardial T-2 mapping. MethodsMyocardial T-2 mapping is commonly performed by acquisition of multiple T(2)prep bSSFP images and estimating the voxel-wise T-2 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(2)prep RF pulses, which may decrease the robustness of T-2 mapping. Therefore, we propose a novel T-2 mapping sequence that incorporates an additional image acquired with saturation preparation, simulating a very long T(2)prep echo time. This enables the robust estimation of T-2 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-2 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. ResultsPhantom and in vivo data show that the T-2 values generated by the proposed 3-parameter model fitting do not change with different choices of the T(2)prep echo times, and are not statistically different than the reference values for the phantom (P=0.10 with three T(2)prep echoes). The two-parameter model exhibits dependence on the choice of T(2)prep echo times and are significantly different than the reference values (P=0.01 with three T(2)prep echoes). ConclusionThe proposed imaging sequence in combination with a three-parameter model allows accurate measurement of myocardial T-2 values, which is independent of number and duration of T(2)prep echo times. Magn Reson Med 74:93-105, 2015. (c) 2014 Wiley Periodicals, Inc.