A DERIVED RELAXATION CONTRAST FROM SYNTHETIC MRI FOR DETECTING NETWORK MICROSTRUCTURAL VULNERABILITY.

Area of Science:

• Neuroimaging
• Alzheimer's Disease Research
• Neurodegeneration

Background:

• Odor identification impairment is an early marker of Alzheimer's disease (AD), predicting memory decline.
• The microstructural basis of this impairment, particularly in mild cognitive impairment (MCI), is not well understood.
• Early myelin and lipid disruption in olfactory and limbic circuits may underlie these changes.

Purpose of the Study:

• To investigate early myelin and lipid disruption in MCI using a novel synthetic MRI contrast.
• To assess the utility of this contrast, FD (FLAIR-derived metric), in detecting microstructural changes.
• To determine if FD complements myelin volume fraction (MVF) in identifying early AD-related changes.

Main Methods:

• Thirty-three older adults (16 healthy controls, 17 MCI) underwent olfactory/cognitive testing and 3T brain MRI.
• A synthetic MRI contrast (FD) was computed from FLAIR and DIR images.
• Region-of-interest and voxel-wise analyses examined FD and MVF differences and their association with odor identification.

Main Results:

• MCI patients showed significantly lower FD in olfactory and limbic regions (hippocampus, amygdala, orbitofrontal cortex, thalamus, corpus callosum) compared to controls.
• FD demonstrated moderate discrimination between MCI and controls, comparable to MVF.
• Higher FD in specific brain regions correlated with better odor identification, independent of MVF.

Conclusions:

• FD is a practical, myelin- and lipid-sensitive MRI contrast complementary to MVF.
• FD captures variance beyond local myelin content, potentially improving early detection of microstructural changes in MCI.
• FD shows promise as a scalable marker linking network disruption to olfactory symptoms in the AD continuum.