Phantom- and simulation-based validation of combined diffusion relaxometry in ex vivo ADRD white matter

Abstract

PurposeIn principle, combined T2-Diffusion (D) MRI has the microstructural and chemical sensitivity to detect axonal and myelin water changes in Alzheimers disease and related dementias (ADRD), but its practical implementation may be hindered by demanding hardware requirements. This work assesses the feasibility and accuracy of T2-D for ex vivo analysis of WM lesions in ADRD tissue. MethodsA thawed ex vivo brain sample from the Michigan Brain Bank and a T2-D phantom were scanned at 7T using a combined diffusion relaxometry (CDR) sequence. A non-negative least squares (NNLS) conventional data processing pipeline was used to disentangle water pools with unique T2-D signatures. Simulations examined the effects of minimum TE and SNR on recovery of myelin water (short T2, slow diffusion). ResultsAcross tissue types, T2-D data consistently resolved three spectral components. Phantom experiments showed detection of short T2 and slow diffusion features similar to those observed in ADRD ex vivo tissue, and confirmed CDRs ability to accurately resolve multiple components. Simulations indicated reliable T2-D recovery for myelin with SNR > 30 dB and minimum TE < 25 ms. ConclusionStrong T2 and D weighting could be combined to capture the expected axonal, myelin, and extracellular (EC) regions in T2-D space. The observed short-T2, restricted-D components are therefore unlikely to be artifacts and instead support interpretations as physically meaningful myelin and axonal water signatures.