T 2 mapping with magnetization‐prepared 3D TSE based on a modified BIR‐4 T 2 preparation

The purpose of this work was to investigate the performance of the modified BIR‐4 T 2 preparation for T 2 mapping and propose a method to remove T 2 quantification errors in the presence of large B 1 and B 0 offsets. The theoretical investigation of the magnetization evolution during the T 2 preparation in the presence of B 1 and B 0 offsets showed deviations from a mono‐exponential T 2 decay (two parameter fit). A three parameter fit was used to improve T 2 accuracy. Furthermore, a two parameter fit with an additional saturation preparation scan was proposed to improve T 2 accuracy and precision. These three fitting methods were compared based on simulations, phantom measurements and an in vivo healthy volunteer study of the neck musculature using a 3D TSE readout. The results based upon the pure two parameter fit overestimated T 2 in regions with high B 0 offsets (up to 40% in phantoms). The three parameter fit T 2 values were robust to B 0 offsets but with higher standard deviation (up to 40% in simulations). The two parameter fit with the saturation preparation yielded high robustness towards B 0 offsets with a noise performance comparable to that of the two parameter fit. In the volunteer study the T 2 values obtained by the pure two parameter fit showed a dependence on the field inhomogeneities, whereas the T 2 values from the proposed fitting approach were shown to be insensitive to B 0 offsets. The proposed method enabled accurate and precise T 2 mapping in the presence of large B 1 and B 0 offsets.