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Optimising imaging parameters for post mortem MR imaging of the human brain
A M Blamire1, J G Rowe, P Styles
1Department of Biochemistry, University of Oxford, United Kingdom.
Purpose:
MR imaging of post mortem brains has the potential to yield volumetric information and define the extent of structural changes prior to pathological examination. Although standard T2-weighted clinical imaging sequences have been used for the examination of formalin-fixed brains, these protocols may not yield optimum contrast. We examined the effect of varying durations of formalin fixation on the transverse relaxation time (T2) and the tissue spin density.
Material And Methods:
Three post mortem brains were examined weekly during formalin fixation from the unfixed state to 35 days fixation. Standard MR spin-echo imaging was used at 5 echo times (20-100 ms) to calculate transverse relaxation time (T2) and spin density.
Results:
T2 decreased significantly (ANOVA, p<0.001) in both grey and white matter by 7 days fixation and there was a further (but non-significant) trend towards lower values between 7 and 35 days. Grey and white matter T2 times converged with fixation. Conversely, the grey to white matter spin density ratio increased from 1.19+/-0.01 to 1.54+/-0.06 over five weeks of fixation.
Conclusion:
Our results suggest that spin density-weighted imaging sequences would provide improved grey to white matter contrast over T2-weighted sequences.
Insights
Formalin fixation alters magnetic resonance (MR) imaging properties of postmortem brains. Spin density-weighted sequences offer better contrast than T2-weighted sequences for examining fixed brain tissue.
Area of Science:
- Neuroimaging
- Pathology
- Biophysics
Background:
- Postmortem brain MR imaging aids in assessing structural changes before pathological examination.
- Standard T2-weighted sequences may not provide optimal contrast for formalin-fixed brains.
Purpose of the Study:
- To investigate the impact of formalin fixation duration on transverse relaxation time (T2) and spin density in postmortem brains.
- To evaluate MR imaging contrast in formalin-fixed brain tissue.
Main Methods:
- Three postmortem brains were imaged weekly during 35 days of formalin fixation.
- Standard MR spin-echo imaging with 5 echo times (20-100 ms) was employed.
- Transverse relaxation time (T2) and spin density were calculated.
Main Results:
- Transverse relaxation time (T2) significantly decreased in grey and white matter within 7 days of fixation.
- Grey and white matter T2 values converged over time.
- The grey to white matter spin density ratio increased from 1.19 to 1.54 over five weeks.
Conclusions:
- Spin density-weighted MR imaging sequences enhance grey to white matter contrast compared to T2-weighted sequences.
- This improved contrast is beneficial for analyzing structural changes in formalin-fixed postmortem brains.