Myelin water imaging by magnetic resonance imaging provides a non-invasive surrogate measure of myelin content in brain tissue. The myelin water fraction (MWF) is derived from multicomponent T2 relaxometry and represents the proportion of the MR signal arising from water trapped between myelin lamellae. Postmortem imaging permits more direct validation of MRI-derived myelin metrics against neuropathological standards, making it an important step for establishing sequence validity in contexts where tissue fixation and ex vivo conditions differ from in vivo scanning.
The study aimed to validate and compare two MRI approaches—turbo spin echo (TSE) and gradient-and-spin-echo (GRASE)—for myelin water imaging in formaldehyde-fixed postmortem human brains. The explicit goal was to determine the applicability of these sequences for estimating MWF in ex vivo tissue and to assess agreement between measures derived from each sequence type.
Forty postmortem human brain hemispheres were included in the imaging study. The brains were formaldehyde fixed prior to MRI. Further sample-level details such as donor demographics, postmortem interval, fixation duration, and neuropathological diagnoses were not reported in the provided source excerpt.
Each hemisphere was scanned using both a TSE sequence and a GRASE sequence. The rationale for comparing these two families of sequences is that TSE and GRASE use different mechanisms for refocusing and echo generation, which can influence T2 decay sampling, signal-to-noise characteristics, and sensitivity to tissue microstructure in multicomponent T2 analyses.
Specific acquisition parameters (for example, repetition time, echo times, number of echoes for TSE, spatial resolution, field strength, and other protocol details) were not reported in the provided text.
Acquired data were reconstructed using a non-parametric multicomponent T2 relaxometry approach. The same reconstruction framework was applied to both GRASE- and TSE-derived data to support direct comparison between measures. Applying a consistent reconstruction pipeline reduces methodological variability that could confound sequence comparisons and focuses the analysis on the influence of the acquisition strategy itself.
Agreement between derived MWF measures was quantified at both the voxel level and the regional level. This indicates the authors assessed concordance of MWF values across sequences in localized voxels and also aggregated values within anatomically or functionally defined regions of interest.
The excerpt does not include details on which regional parcellations were used, how regions were defined, whether any registration to a common space was performed, nor the specific metrics used to quantify agreement (for example, correlation coefficients, Bland–Altman limits, or intraclass correlation). Those specifics were not reported in the provided source text.
For GRASE, the authors compared maps produced from a full 32-echo reconstruction with maps from a truncated 14-echo reconstruction. This comparison addresses how echo-sampling density and T2 sampling range affect the estimated MWF in ex vivo tissue, which can be particularly important where scan time, SNR, or hardware limitations constrain echo trains.
Details such as how echoes were selected for truncation, whether the 14-echo subset was evenly spaced or truncated from the tail, and the quantitative impact on MWF metrics were not provided in the excerpt.
The provided source excerpt does not include numeric results, statistical outcomes, sample-level findings, or example images. Therefore, specific findings regarding the degree of agreement between TSE- and GRASE-derived MWF, the effect of echo truncation on GRASE results, or any associations with neuropathological measures are not available from the excerpt and cannot be reported here.
Based on the provided text, several important methodological and result-oriented details are missing and were not reported in the excerpt:
Where these items are essential to interpret the study, readers should consult the full preprint or contact the authors for complete methodological and result details.
From the excerpted abstract, the study establishes a framework for comparing TSE and GRASE sequences for ex vivo myelin water imaging using a consistent non-parametric multicomponent T2 relaxometry reconstruction. The work leverages a substantial sample of 40 fixed hemispheres and explicitly examines the influence of echo sampling in GRASE (32 versus 14 echoes). The full outcomes and their implications for postmortem validation of MWF or translation to in vivo protocols were not included in the provided text. For readers seeking to understand sequence performance, methodological trade-offs, or the degree of concordance between TSE- and GRASE-derived MWF, the full manuscript should be consulted to access the quantitative results and any neuropathological validation.