Gray-white matter contrast reversal on T₁-weighted spin-echo in postmortem brain

Area of Science:

• Radiology
• Neuroscience
• Forensic Science

Background:

• Postmortem MRI contrast differs from antemortem MRI due to physiological changes and scanning conditions.
• Gray matter (GM) and white matter (WM) contrast is reversed in postmortem T1-weighted spin-echo (T1WSE) images compared to living subjects.
• The underlying cause of this GM-WM contrast reversal in postmortem brains is not well understood.

Purpose of the Study:

• To investigate and clarify the reasons behind the observed contrast reversal between GM and WM in postmortem brain MRI.
• To determine the key factors contributing to the altered signal intensities in postmortem brain tissues.

Main Methods:

• Postmortem T1W-SE MRI of the brain was performed on 23 corpses using a 1.5T MRI system.
• T1 and T2 relaxation times, as well as proton density (PD), of GM and WM were measured in the basal ganglia region.
• Measurements were conducted at low body temperatures (mean 6.9°C) prior to medico-legal autopsy.

Main Results:

• All postmortem brains exhibited inverted GM-WM contrast on T1W-SE images compared to the living brain.
• T1 relaxation times decreased in both GM and WM postmortem, with WM/GM ratio remaining below 1.
• Proton density (PD) significantly decreased in both GM and WM postmortem, with a notable decrease in the WM/GM ratio. T2 values showed no significant difference from the living brain.

Conclusions:

• The significant decrease in proton density (PD) of both gray and white matter is identified as the primary factor driving the contrast reversal observed in postmortem brain MRI.
• Understanding these changes is crucial for accurate interpretation of postmortem neuroimaging findings.