Multicenter reproducibility of quantitative susceptibility mapping of the entorhinal cortex and hippocampal subfields at 7T MRI

Abstract

AbstractBackgroundT2*‐weighted MRI images can be processed to produce quantitative susceptibility maps (QSM). These reflect iron and myelin concentrations, which are disturbed in neurodegenerative cascade and Amyloidb/tau pathological states. Changes in susceptibility have been measured in various regions of the brain in association with ADRD disease severity [Kim, et al.NeuroImage: Clinical. 2017], particularly in the hippocampus, amygdala, precuneus and thalamus, but no study has focused on subfields of the hippocampus in ADRD. As part of the UK7T Network’s “Travelling Heads” study [Clarke, et al. NeuroImage 2020], our aim here was to assess the inter‐subject and inter‐site reproducibility of QSM mapping at 7T in the entorhinal cortex, hippocampal subfields, and dentate gyrus preparing for future multi‐site clinical studies of Alzheimer’s disease and Related Dementias (ADRD).MethodTen healthy volunteers (3 female, 7 males; age 32.0±5.9 years) were scanned using harmonized single‐echo T2*‐weighted gradient echo, T1‐weighted and T2‐weighted sequences, as described in [Clarke, et al. NeuroImage 2020]. Participants were scanned five times at their “home” site on one of the following 7T MRI scanners: 1xPhilips, 2xSiemens Magnetom, 2xSiemens Terra scanners.ASHS [Yushkevich, et al. Human Brain Mapping. 2015] was used to segment the hippocampus from the combination of the high resolution T1 and T2 weighted data and a detailed atlas. The volume of each subfield was obtained from the segmentation using FSL (in CA2 and CA3 sub‐volumes were too small for these regions to be included in the susceptibility analysis.).QSM maps of the whole brain were produced using Multi‐Scale Dipole inversion (MSDI) [Acosta‐Cabronero, et al. NeuroImage. 2018] and the average and standard deviation of the susceptibility in each sub‐field in each scan was extracted.ResultThe median intraclass correlation coefficient (ICC) value for the susceptibility for each subfield was found to be 0.84, 0.48, 0.71, 0.83 and 0.78 for entorhinal cortex (ERC), subiculum (SUB), CA1, dentate gyrus (DG) and Tail, respectively.ConclusionSusceptibility can be measured with good reproducibility for the hippocampal subfields and entorhinal cortex in healthy subjects and this protocol can now be translated to clinical studies of ADRD.