In-vivo histology with MRI

MRI is a non invasive technology that can be used safely in live individuals for the study of the brain. Our research aims to enable the use of MRI to measure microscopic properties of the brain (e.g. cell size, fibre myelination,...). Our objective is to allow the study of microscopic brain changes due to neurodegenerative diseases and improve diagnostics. 

Characterizing the distribution of iron within brain tissue

Reference

Oliveira R, Raynaud Q, Kiselev V, Jelescu I, Lutti A. Non-exponential transverse relaxation in the brain’s basal ganglia. 32nd Annual Meeting of the International Society for Magnetic Resonance in Medicine, Toronto, Canada 2598 (2023).

Oliveira R, Raynaud Q, Kiselev V, Jelescu IO, Lutti A. Non-exponential transverse relaxation decay in subcortical grey matter. Preprint at https://doi.org/10.1101/2023.09.15.557912 (2023).

Recent work from our group has shown that, contrary to a widely shared assumption, decay of the MRI signal due to transverse relaxation is not exponential in sub-cortical grey matter. This non-exponential signal decay allows the assessment of the microscopic distribution of iron within the tissue:

This fingerprint of iron distribution allows new insights into the physiological changes involving iron that take place within brain tissue. Because MRI is non-invasive, these changes can be monitored in vivo in live individuals.

Applications for this work are numerous. It will provide new insights into the physiological mechanisms underlying the increase in iron concentration with healthy ageing. It will also enable new investigations of the role of iron homeostasis in neurodegenerative diseases such as Parkinson’s Disease or Alzheimer's Disease and facilitate disease staging.


Measuring the morphology of axonal fibers from in-vivo MRI and EEG data

The biophysical model introduced by our group use MRI and EEG data acquired in-vivo in patients to estimate the radius distribution (P(r)) and thickness of the myelin sheath (g(r)) of axonal fibers, opening new avenues for the study of neurodegenerative diseases. 

The radius of axons and the thickness of their myelin sheath determine the speed of conduction of neuronal signals, and are essential to brain development and brain function. Demyelinating diseases such as multiple sclerosis have widespread consequences on cognitive and motor function. MRI biomarkers myelination exist that allow the monitoring of myelin concentration change in-vivo in patient populations. However, these markers only provide bulk measures of myelin concentration, with no insight into the cellular mechanisms underlying myelination changes (e.g. neural loss, thinning of the myelin sheath,...).  

Novel markers of axonal morphology, with improved specificity, require biophysical models of the MRI signal. Our group is currently developing such models, based on MRI and EEG data acquired in-vivo in patients. These models provide estimates of the distribution of axonal radius (P(r)) and of the thickness of the myelin sheath (g(r)), opening new avenues for the study of neurodegenerative diseases and for the combined study of brain structure and brain function.

Reference

Oliveira AR, Pelentritou A, Di Domenicantonio G, De Lucia M., Lutti A. In vivo Estimation of Axonal Morphology From Magnetic Resonance Imaging and Electroencephalography Data. Front Neurosci (2022).  DOI: 10.3389/fnins.2022.874023

Oliveira AR, De Lucia M., Lutti A. Single-subject electroencephalography measurement of interhemispheric transfer time for the in-vivo estimation of axonal morphology Human Brain Mapping (2023). DOI: 10.1002/hbm.26420