Histology to MRI registration quality of ex vivo human brain blocks fixed with solutions used in anatomy laboratories
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Introduction
Post-mortem brain tissue is obtained from brain banks that provide small tissue samples, while gross anatomy laboratories could become a source of complete brains for neuroscientists. These are preserved with solutions whose chemical composition differs from the classic neutral-buffered formalin (NBF) used in brain banks, such as a saturated-salt-solution (SSS) or an alcohol-formaldehyde solution (AFS) that preserve antigenicity of the main brain cell populations. Since histology remains the gold standard in neuroscientific research, while MRI is the most common imaging modality, MRI-histology registration quality needs to be assessed to ensure the suitability using brains fixed with innovative solutions for research procedures. Hence, our goal was to compare the registration quality of human brains fixed with NBF, SSS and AFS, as well as the histological characteristics that could affect the registration.
Methods
We used 12 human brain blocks of 3×3×3 cm 3 fixed in our anatomy laboratory using SSS (N=4), AFS (N=4), or NBF (N=4). The blocks were scanned using a 7Tesla Bruker animal MRI scanner with a T2-TurboRARE sequence at 0.13×0.13×0.5mm 3 . Blocks were then cut into 40μm thick sections (parallel to the 0.13×0.13 plane) using a vibratome. Sections were stained with histochemistry (HC) (Cresyl violet, Prussian blue, Luxol fast blue, H&E, and Bielschowsky) and immunohistochemistry (IHC) of the 4 main cell populations: neurons (NeuN), astrocytes (GFAP), microglia (Iba1) and myelin (PLP) either with or without an antigen retrieval (AR) protocol. Stained sections were imaged using a slide scanner microscope and segmented with masks using Display, and the sections were manually registered to the T2-TurboRare images using landmarks in Register (MincToolKit).
Results
More landmarks were needed to achieve proper alignment of the histology to MRI images for the SSS-fixed blocks, due to the lower GM-WM contrast in these brains. However, there was no significant difference in the staining intensity of the histology sections of blocks fixed with the three solutions, while SSS-fixed blocks showed a lower percentage of overlap between the good histology quality masks and the MRI masks. This resulted in a sufficient registration quality of all blocks, although more challenging when fixed with SSS.
Conclusion
We have developed histology, MRI and registration protocols that are of good quality in brain blocks fixed with solutions used in gross anatomy laboratories. These results are promising for neuroscientists interested in using full brains from anatomy laboratories, either using MRI, histology or registration of both modalities to study normal aging and neurodegenerative conditions.
