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Effects of concentration and vendor specific composition of formalin on postmortem MRI of the human brain
Christoph Birkl1, Martin Soellradl1, Anna Maria Toeglhofer2
1Department of Neurology, Medical University of Graz, Austria.
Purpose:
Formalin fixation prevents tissue autolysis by crosslinking proteins and changes tissue microstructure and MRI signal characteristics. Previous studies showed high variations in MR relaxation time constants of formalin fixed brain tissue, which has been attributed to the use of different formalin concentrations. Our investigations confirmed the influence of formalin concentration on relaxation times and unexpectedly revealed an influence of vendor specific formalin composition, which has not been investigated so far.
Methods:
We systematically analyzed relaxation times of human brain tissue fixed with 4% and 10% formalin compared with unfixed condition at 3 Tesla MRI. Furthermore, we assessed relaxation times of nine formalin solutions from different vendors and performed comparisons of their magnetic susceptibility by SQUID (superconducting quantum interference device) magnetometry.
Results:
Tissue relaxation times decreased approximately twice as fast using 10% than in 4% formalin fixation. The vendor specific composition of the formalin solutions and concentration dependent paramagnetic effects showed a substantial contribution to differences in relaxation times of formalin.
Conclusion:
Our study demonstrates that differences of the formalin composition have substantial effects on MRI signal characteristics after fixation, which can explain the divergence of reported relaxation times beyond the effect of differences in formalin concentration. Magn Reson Med 79:1111-1115, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Insights
Formalin fixation affects MRI relaxation times. Variations in formalin composition, not just concentration, significantly impact these MRI signal characteristics in fixed brain tissue.
Area of Science:
- Biomedical Imaging
- Materials Science
Background:
- Formalin fixation is crucial for preserving tissue structure by crosslinking proteins, preventing autolysis.
- Formalin fixation alters tissue microstructure and magnetic resonance imaging (MRI) signal characteristics, including relaxation times.
- Previous research noted significant variability in MR relaxation times of formalin-fixed brain tissue, often attributed to differing formalin concentrations.
Purpose of the Study:
- To investigate the influence of formalin concentration and vendor-specific formalin composition on MRI relaxation times of human brain tissue.
- To systematically analyze relaxation times in unfixed, 4% formalin-fixed, and 10% formalin-fixed human brain tissue at 3 Tesla MRI.
- To compare the magnetic susceptibility of formalin solutions from different vendors.
Main Methods:
- Systematic analysis of human brain tissue relaxation times using 3 Tesla MRI.
- Comparison of tissue fixed with 4% and 10% formalin against unfixed controls.
- Assessment of relaxation times and magnetic susceptibility (using SQUID magnetometry) of nine formalin solutions from various vendors.
Main Results:
- Tissue relaxation times decreased approximately twice as rapidly with 10% formalin fixation compared to 4% formalin.
- Vendor-specific formalin composition significantly contributed to differences in relaxation times, beyond concentration-dependent paramagnetic effects.
- Paramagnetic effects related to formalin concentration were identified as a substantial factor influencing relaxation times.
Conclusions:
- Differences in formalin composition substantially affect MRI signal characteristics post-fixation.
- Variations in formalin composition can explain the divergence in reported MR relaxation times, independent of formalin concentration.
- Understanding formalin composition is critical for accurate interpretation of MRI data from fixed tissues.