Microstructural imaging in temporal lobe epilepsy: Diffusion imaging changes relate to reduced neurite density.

Area of Science:

• Neuroimaging
• Epilepsy Research
• Biomarker Discovery

Background:

• Refractory temporal lobe epilepsy (TLE) presents challenges in understanding underlying neurobiology.
• Conventional imaging like DTI has limitations in specificity for TLE-related changes.
• Multi-compartment models offer more specific insights into neuronal density and myelination.

Purpose of the Study:

• To investigate the spatial distribution of conventional and novel MRI metrics in TLE.
• To correlate advanced metrics like neurite density (NODDI) and myelin water fraction (MWF) with conventional DTI findings.
• To infer the neurobiological basis of imaging changes in refractory TLE.

Main Methods:

• Acquired multi-shell diffusion MRI and mcDESPOT data from 20 TLE patients and 20 controls.
• Derived diffusion tensor imaging (DTI), Neurite Orientation Dispersion and Density Imaging (NODDI), and myelin water fraction (MWF) metrics.
• Analyzed metrics from intracortical grey matter and subcortical white matter surfaces, alongside cortical thickness.

Main Results:

• Increased diffusivity in TLE grey matter correlated with reduced neurite density and CSF partial volume effects.
• Subcortical white matter showed reduced fractional anisotropy and increased radial diffusivity, linked to decreased neurite density and MWF.
• Cortical thickness reductions were observed but unrelated to neurite density or MWF.

Conclusions:

• Diffusivity alterations in TLE are primarily driven by reduced neurite density.
• Reduced myelin water fraction also contributes to white matter changes in specific temporal regions.
• Neurite density shows promise as a sensitive biomarker for progressive neuronal damage in refractory TLE.