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Published on: January 17, 2019
The choice of embedding media affects image quality, tissue R2* , and susceptibility behaviors in post-mortem brain
Petr Dusek1,2, Vince Istvan Madai3, Till Huelnhagen4
1Department of Neurology, Charles University, 1st Faculty of Medicine and General University Hospital in Prague, Praha, Czech Republic.
Purpose:
The quality and precision of post-mortem MRI microscopy may vary depending on the embedding medium used. To investigate this, our study evaluated the impact of 5 widely used media on: (1) image quality, (2) contrast of high spatial resolution gradient-echo (T1 and T2* -weighted) MR images, (3) effective transverse relaxation rate (R2* ), and (4) quantitative susceptibility measurements (QSM) of post-mortem brain specimens.
Methods:
Five formaldehyde-fixed brain slices were scanned using 7.0T MRI in: (1) formaldehyde solution (formalin), (2) phosphate-buffered saline (PBS), (3) deuterium oxide (D2 O), (4) perfluoropolyether (Galden), and (5) agarose gel. SNR and contrast-to-noise ratii (SNR/CNR) were calculated for cortex/white matter (WM) and basal ganglia/WM regions. In addition, median R2* and QSM values were extracted from caudate nucleus, putamen, globus pallidus, WM, and cortical regions.
Results:
PBS, Galden, and agarose returned higher SNR/CNR compared to formalin and D2 O. Formalin fixation, and its use as embedding medium for scanning, increased tissue R2* . Imaging with agarose, D2 O, and Galden returned lower R2* values than PBS (and formalin). No major QSM offsets were observed, although spatial variance was increased (with respect to R2* behaviors) for formalin and agarose.
Conclusions:
Embedding media affect gradient-echo image quality, R2* , and QSM in differing ways. In this study, PBS embedding was identified as the most stable experimental setup, although by a small margin. Agarose and Galden were preferred to formalin or D2 O embedding. Formalin significantly increased R2* causing noisier data and increased QSM variance.
Insights
The choice of embedding medium significantly impacts post-mortem MRI microscopy quality. Phosphate-buffered saline (PBS) offered the most stable results for gradient-echo imaging and quantitative susceptibility mapping.
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Materials Science
Background:
- Post-mortem MRI microscopy requires precise sample preparation.
- The embedding medium can influence image quality and quantitative measurements.
Purpose of the Study:
- To evaluate the impact of five embedding media on post-mortem brain MRI microscopy.
- Assessed effects on image quality, contrast, relaxation rates (R2*), and quantitative susceptibility mapping (QSM).
Main Methods:
- Five formaldehyde-fixed brain slices were scanned using 7.0T MRI.
- Tested media included formalin, phosphate-buffered saline (PBS), deuterium oxide (D2O), perfluoropolyether (Galden), and agarose gel.
- Analyzed signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), R2*, and QSM.
Main Results:
- PBS, Galden, and agarose yielded higher SNR/CNR than formalin and D2O.
- Formalin increased tissue R2* and QSM variance, leading to noisier data.
- Agarose, D2O, and Galden resulted in lower R2* values compared to PBS and formalin.
Conclusions:
- Embedding media significantly influence gradient-echo image quality, R2*, and QSM.
- PBS provided the most stable experimental setup for post-mortem MRI.
- Agarose and Galden are preferable to formalin or D2O for improved imaging outcomes.
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