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Updated: Mar 26, 2026
High-resolution Structural Magnetic Resonance Imaging of the Human Subcortex In Vivo and Postmortem
Published on: December 30, 2015
Effects of formalin fixation and temperature on MR relaxation times in the human brain
Christoph Birkl1, Christian Langkammer1,2, Nicole Golob-Schwarzl3
1Department of Neurology, Medical University of Graz, Austria.
Abstract:
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.
Insights
Formalin fixation significantly alters brain tissue relaxation times (T1, T2, T2*), primarily due to protein crosslinking, not water content changes. This impacts post-mortem MRI comparability and requires protocol optimization.
Area of Science:
- Neuroscience
- Biophysics
- Medical Imaging
Background:
- Post-mortem MRI is crucial for understanding disease-induced brain tissue changes.
- Formalin fixation and temperature variations can affect MRI comparability with in vivo studies.
Purpose of the Study:
- To investigate the effects of formalin fixation and temperature on T1, T2, and T2* relaxation times in brain tissue.
- To elucidate the mechanisms behind these changes, focusing on water content and protein crosslinking.
Main Methods:
- Relaxometry measurements on post-mortem brain slices at various temperatures.
- Repetition of measurements after prolonged formaldehyde immersion (190 days).
- Determination of water content (wet-to-dry ratio) and protein analysis (SDS-PAGE).
Main Results:
- Formalin fixation markedly decreased all relaxation times, with T1 reduction up to 76%.
- Protein crosslinking, indicated by increased protein size (>260 kDa), was identified as the primary cause of T1 shortening.
- Temperature coefficients for T1 and T2 showed distinct changes after fixation, suggesting altered molecular dynamics.
Conclusions:
- Formalin fixation-induced protein crosslinking, rather than water content changes, significantly alters brain tissue relaxation times.
- Understanding these fixation-induced effects is essential for optimizing post-mortem MRI protocols and ensuring data comparability.
- The provided relaxation time data can aid in refining neuroimaging techniques for post-mortem analysis.
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