Elsevier

NeuroImage

Volume 56, Issue 3, 1 June 2011, Pages 974-983
NeuroImage

Structural correlates of active-staining following magnetic resonance microscopy in the mouse brain

https://doi.org/10.1016/j.neuroimage.2011.01.082Get rights and content
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open access

Abstract

Extensive worldwide efforts are underway to produce knockout mice for each of the ~ 25,000 mouse genes, which may give new insights into the underlying pathophysiology of neurological disease. Microscopic magnetic resonance imaging (μMRI) is a key method for non-invasive morphological phenotyping, capable of producing high-resolution 3D images of ex-vivo brains, after fixation with an MR contrast agent. These agents have been suggested to act as active-stains, enhancing structures not normally visible on MRI. In this study, we investigated the structural correlates of the MRI agent Gd-DTPA, together with the optimal preparation and scan parameters for contrast-enhanced gradient-echo imaging of the mouse brain. We observed that in-situ preparation was preferential to ex-situ due to the degree of extraction damage. In-situ brains scanned with optimised parameters, enabled images with a high signal-to-noise-ratio (SNR ~ 30) and comprehensive anatomical delineation. Direct correlation of the MR brain structures to histology, detailed fine histoarchitecture in the cortex, cerebellum, olfactory bulb and hippocampus. Neurofilament staining demonstrated that regions of negative MR contrast strongly correlated to myelinated white-matter structures, whilst structures of more positive MR contrast corresponded to areas with high grey matter content. We were able to identify many sub-regions, particularly within the hippocampus, such as the unmyelinated mossy fibres (stratum lucidum) and their region of synapse in the stratum pyramidale, together with the granular layer of the dentate gyrus, an area of densely packed cell bodies, which was clearly visible as a region of hyperintensity. This suggests that cellular structure influences the site-specific distribution of the MR contrast agent, resulting in local variations in T2*, which leads to enhanced tissue discrimination. Our findings provide insights not only into the cellular distribution and mechanism of MR active-staining, but also allow for three dimensional analysis, which enables interpretation of magnetic resonance microscopy brain data and highlights cellular structure for investigation of disease processes in development and disease.

Research highlights

► Investigated preparation and MR parameters for contrast-enhanced mouse brain imaging. ► Also investigated correlates of active-staining for optimised imaging of mouse brain. ► In-situ brains scanned with optimised parameters enabled detailed, high SNR images. ► Correlated MR brain structures to histology, detailing fine histoarchitecture visible. ► Our findings may provide insights into the cellular distribution of MR active-stains.

Abbreviations

MRI
magnetic resonance imaging
CNS
central nervous system
Gd-DTPA
gadolinium-diethylene-triamine-pentaacetic acid
SNR
signal-to-noise ratio
CNR
contrast-to-noise ratio
FOV
field of view
NSA
number of signal averages
TE
echo time
TR
repetition time
FA
flip angle

Keywords

Magnetic resonance microscopy
Mouse brain phenotyping
Active staining
Mouse brain histology
Immunohistochemistry
Myelin
Grey matter

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