The choice of embedding media affects image quality, tissue R2 * , and susceptibility behaviors in post-mortem brain MR microscopy at 7.0T.
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.
['Dusek|Petr|P|0000-0003-4877-9642', 'Madai|Vince Istvan|VI|', 'Huelnhagen|Till|T|', 'Bahn|Erik|E|', 'Matej|Radoslav|R|', 'Sobesky|Jan|J|', 'Niendorf|Thoralf|T|', 'Acosta-Cabronero|Julio|J|', 'Wuerfel|Jens|J|']
D000368:Aged D001344:Autopsy D001921:Brain D001931:Brain Mapping D003287:Contrast Media D017666:Deuterium Oxide D004987:Ethers D005260:Female D005466:Fluorocarbons D005557:Formaldehyde D006801:Humans D007091:Image Processing, Computer-Assisted D008279:Magnetic Resonance Imaging D008297:Male D008875:Middle Aged D010710:Phosphates D012685:Sepharose D059629:Signal-To-Noise Ratio D013048:Specimen Handling D016610:Tissue Embedding
ex vivo imaging formaldehyde fixation post-mortem imaging quantitative susceptibility mapping ultra-high field MRI