Background Adipose tissue (AT) can be classified into white and brown/beige subtypes. Chemical shift encoding‐based water–fat MRI‐techniques allowing simultaneous mapping of proton density fat fraction (PDFF) and T2* result in a lower PDFF and a shorter T2* in brown compared with white AT. However, AT T2* values vary widely in the literature and are primarily based on 6‐echo data. Increasing the number of echoes in a multiecho gradient‐echo acquisition is expected to increase the precision of AT T2* mapping. Purpose 1) To mitigate issues of current T2*‐measurement techniques through experimental design, and 2) to investigate gluteal and supraclavicular AT T2* and PDFF and their relationship using a 20‐echo gradient‐echo acquisition. Study Type Prospective. Subjects Twenty‐one healthy subjects. Field Strength/Sequence Assessment First, a ground truth signal evolution was simulated from a single‐T2* water–fat model. Second, a time‐interleaved 20‐echo gradient‐echo sequence with monopolar gradients of neck and abdomen/pelvis at 3 T was performed in vivo to determine supraclavicular and gluteal PDFF and T2*. Complex‐based water–fat separation was performed for the first 6 echoes and the full 20 echoes. AT depots were segmented. Statistical Tests Mann‐Whitney test, Wilcoxon signed‐rank test and simple linear regression analysis. Results Both PDFF and T2* differed significantly between supraclavicular and gluteal AT with 6 and 20 echoes (PDFF: P < 0.0001 each, T2*: P = 0.03 / P < 0.0001 for 6/20 echoes). 6‐echo T2* demonstrated higher standard deviations and broader ranges than 20‐echo T2*. Regression analyses revealed a strong relationship between PDFF and T2* values per AT compartment (R2 = 0.63 supraclavicular, R2 = 0.86 gluteal, P < 0.0001 each). Data Conclusion The present findings suggest that an increase in the number of sampled echoes beyond 6 does not affect AT PDFF quantification, whereas AT T2* is considerably affected. Thus, a 20‐echo gradient‐echo acquisition enables a multiparametric analysis of both AT PDFF and T2* and may therefore improve MR‐based differentiation between white and brown fat. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:424–434.

The incorporation of the proposed adiabatic iMSDE-based motion sensitization was shown to provide robust blood suppression of vessels in close proximity to brachial plexus nerves. The use of STIR iMSDE 3D TSE can be considered for clinical MRN examinations of the brachial plexus.

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