![]() Post-mortem MRI provides the opportunity to acquire high-resolution datasets to investigate neuroanatomy, and validate the origins of image contrast through microscopy comparisons. ![]() In order to provide post-mortem MRI as an experimental technique to neuroscientists in Oxford, we have had to develop a broad range of underpinning technologies, including: (i) pulse sequences that provide high-quality data under the harsh imaging conditions of post-mortem tissue (McNab et al., 2009 Miller et al., 2011) (ii) analyses that account for the signal formation mechanisms of these sequences (Tendler et al., 2020a Tendler et al., 2020b) or properties unique to post-mortem tissue (iii) experimental approaches that enable the use of ultra-high field MRI to increase SNR for high-resolution imaging (Foxley et al., 2014 Tendler et al., 2020b) (iv) development of custom sample holders to maximize SNR and minimize imaging artifacts (Appendix 3- figure 1 and Appendix 3-figure 2) (v) tools for aligning small 2D microscopy images into 3D whole-brain MRI (Huszar et al., 2019) (vi) strategies for co-analyzing MRI and microscopy data (Howard et al., 2019b Mollink et al., 2017) and (vii) techniques for between-species comparisons Mars et al., 2018). Despite this potential, post-mortem MRI remains a relatively niche approach, in part due to technical challenges and the need for multidisciplinary expertise. Results suggest that DW-SSFP at 7T is a preferential method for acquiring diffusion-weighted data of post-mortem human brain, specifically where the primary region of interest involves crossing white matter tracts. Specifically, tractography streamlines of cortical projections originating from the corpus callosum, corticospinal tract, and superior longitudinal fasciculus were more successful at crossing the centrum semiovale and projected closer to the cortex. These results translate to improved estimates of secondary fiber orientations leading to higher fidelity tractography results compared with data acquired at 3T. Results demonstrate both datasets acquired at 7T had higher SNR and diffusion contrast than data acquired at 3T, and data acquired at higher beff had improved diffusion contrast than at lower beff at 7T. In this work, data of four post-mortem human brains were acquired at 3T and 7T, using DW-SSFP with similar effective b-values (beff~5150s/mm(2)) for inter-field strength comparisons in addition, DW-SSFP data were acquired at 7T with higher beff (~8550s/mm(2)) for intra-field strength comparisons. This is due to the ability of DW-SSFP to overcome signal-to-noise and diffusion contrast losses brought about by tissue fixation related decreases in T2 and ADC. Previous work has demonstrated improvements in data acquired with diffusion-weighted steady-state free precession (DW-SSFP) compared with conventional diffusion-weighted spin echo at 3T. Post-mortem diffusion imaging of whole, human brains has potential to provide data for validation or high-resolution anatomical investigations.
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