Effects of formalin fixation and temperature on MR relaxation times in the human brain

• Published in: NMR in biomedicine Vol. 29; no. 4; pp. 458 - 465
• Main Authors: Birkl, Christoph, Langkammer, Christian, Golob-Schwarzl, Nicole, Leoni, Marlene, Haybaeck, Johannes, Goessler, Walter, Fazekas, Franz, Ropele, Stefan
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.04.2016; Wiley Subscription Services, Inc
• Subjects: Aged; Aged, 80 and over; Brain - diagnostic imaging; Electrophoresis, Polyacrylamide Gel; Female; Formaldehyde - chemistry; formalin fixation; human brain; Humans; Magnetic Resonance Imaging - methods; Male; Middle Aged; MRI; post-mortem MRI; relaxation times; Temperature; Time Factors; Tissue Fixation - methods; Water; temperature; human brain; relaxation times; MRI; formalin fixation; post-mortem MRI
• ISSN: 0952-3480; 1099-1492; 1099-1492
• DOI: 10.1002/nbm.3477

Post‐mortem MRI of the brain is increasingly applied in neuroscience for a better understanding of the contrast mechanisms of disease induced tissue changes. However, the influence of chemical processes caused by formalin fixation and differences in temperature may hamper the comparability with results from in vivo MRI. In this study we investigated how formalin fixation and temperature affect T1, T2 and T2* relaxation times of brain tissue. Fixation effects were examined with respect to changes in water content and crosslinking. Relaxometry was performed in brain slices from five deceased subjects at different temperatures. All measurements were repeated after 190 days of formaldehyde immersion. The water content of unfixed and fixed tissue was determined using the wet‐to‐dry ratio following drying. Protein weight was determined with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE). Fixation caused a strong decrease of all relaxation times, the strongest effect being seen on T1, with a reduction of up to 76%. The temperature coefficient of T1 was lower in the fixed than unfixed tissue, which was in contrast to T2, where an increase of the temperature coefficient was observed following fixation. The reduction of the water content after fixation was in the range of 1–6% and thus not sufficient to explain the changes in relaxation time. Results from SDS‐PAGE indicated a strong increase of the protein size above 260 kDa in all brain structures examined. Our results suggest that crosslinking induced changes of the macromolecular matrix are responsible for T1 shortening and a decreased temperature dependency. The relaxation times provided in this work should allow optimization of post‐mortem MRI protocols for the brain. Copyright © 2016 John Wiley & Sons, Ltd. The effect of formalin fixation on T1, T2 and T2* relaxation times and temperature dependency in human brain tissue. By measuring the water content and the macromolecular size it could be shown that fixation induced shortening of the relaxation times was mainly driven by the changed molecular structure after crosslinking, while dehydration has no effect.