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Abstract
Small-animal MRI with high field strength allows imaging of the living animal. However, spatial resolution in in vivo brain imaging is limited by the scanning time. Measurements of fixated mouse brains allow longer measurement time, but fixation procedures are time consuming, since the process of fixation may take several weeks. We here present a quick and simple post-mortem approach without fixation that allows high-resolution MRI even at 7 Tesla (T2-weighted MRI). This method was compared to in vivo scans with optimized spatial resolution for the investigation of anesthetized mice (T1-weighted MRI) as well as to ex situ scans of fixed brains (T1- and T2-weighted scans) by using standard MRI-sequences, along with anatomic descriptions of areas observable in the MRI, analysis of tissue shrinkage and post-processing procedures (intensity inhomogeneity correction, PCNN3D brain extract, SPMMouse segmentation, and volumetric measurement). Post-mortem imaging quality was sufficient to determine small brain substructures on the morphological level, provided fast possibilities for volumetric acquisition and for automatized processing without manual correction. Moreover, since no fixation was used, tissue shrinkage due to fixation does not occur as it is, e.g., the case by using ex vivo brains that have been kept in fixatives for several days. Thus, the introduced method is well suited for comparative investigations, since it allows determining small structural alterations in the murine brain at a reasonable high resolution even by MRI performed at 7 Tesla.
Highlights
The murine brain is about 3500 times lighter than the human brain and the small brain size challenges high field imaging with high-quality and high spatial resolution
In order to compare the introduced fixationfree post-mortem method with in vivo and ex situ MRI scans, animals were first analyzed using in vivo MRI-scanning [see MRIScanning (In Vivo) section]
We demonstrate that the use of non-fixed post-mortem tissue is well-suited as a quick and sensitive method for high-resolution MRI
Summary
The murine brain is about 3500 times lighter than the human brain and the small brain size challenges high field imaging with high-quality and high spatial resolution. It is possible to anesthetize mice with isoflurane for 6.5 h without any mortality (Szczesny et al, 2004), practically 120 min is the limit for MRI-measurement duration These investigations are accompanied by artifacts due to due to circulation and breathing movements (Johnson et al, 1993; Benveniste and Blackband, 2002). Staining techniques have been developed such as the most commonly used contrast-enhancing agents (Huang et al, 2009; Kim et al, 2009; Cleary et al, 2011) These techniques are well suited to obtain high-quality scans useful, e.g., for creating atlases of the rodent brain (Ma et al, 2005). This may compromise their use for quantitative morphometric analyses, where accurate anatomical volumes and morphology are essential (Cleary et al, 2011)
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