TFE26-563
Quantifying anomalies in patients with neuropathologies via diffusion Magnetic Resonance Imaging. (Application to Alzheimer diagnosis)
Max student :
1 or 2
Promoters:
Benoît Macq
Ce projet sera co-supervisé par Laurence Dricot, logisticienne de recherche et responsable de la résonance magnétique à St Luc.
Description:
Context
The human brain is composed of active neuronal areas connected through “long fibers”, called axons. The information flows through the axons by the movement of polarised water molecules. Recent progresses in Magnetic Resonance Imaging allows to visualize this information flow brought by the moouvement of water molecules. More precisely, diffusion-weighted magnetic resonance imaging (DW-MRI) provides image contrast through measurement of the diffusion properties of water in cells.
Several teams, including those of Gaetan Rensonnet, Maxime Taquet and Benoit Macq at UCL, have developped new and high fidelity efficient models and simulation tools linking the DW-MRI signals to the microstructures of the brain, the water motion being guided by these structures. From these new models and simulation tools, it is possible to develop new DW-MRI signals processing methods to diagnose neurological diseases like multiple sclerosis, Parkinson’s disease or Alzheimer disease. These pathologies are characterized by a decrease of the myelin layer around the axons which augments the free space for water molecules to move. It is also possible to use these signals to provide diagnostic information about brain tumours, replacing a dangerous biopsy, and allowing to “track” the effect of a specific treatment.
Motivation
The human brain is a complex entanglement of interconnected cellular structures including axons, which are “long fibers” usually bundled together in fascicles, and glial cells, which nourish, protect and provide structure to the axons, among others through the production of a myelin sheath (Figure 1 a). The brain microstructure collectively refers to the complex organization of these fascicles of parallel axons and glial cells. Patients suffering from neurodegenerative diseases, such as multiple-sclerosis, or schizophrenia, exhibit microstructural abnormalites, characterized for instance by a loss of myelin or an abnormally-high presence of glial cells.
Diffusion Magnetic Resonance Imaging (dMRI) tries to quantify these microstructural changes in a non-invasive way. Thereto, it uses an imaging modality that measures the tendency of water molecules to flow or diffuse across the tissues in given directions, in the presence of axonal membranes and glial cells.
While there exist many mathematical techniques for characterizing the number, axonal density and main orientation of fascicles, the detection and quantification of myelin and glial cells remains difficult. In fact, most mathematical models of the brain microstructure simply ignore the myelin sheath and glial cells, despite their crucial role in many neurological disorders.
Figure 1 (a) Schematic representation of a healthy axon protected by myelin in the presence of various types of glial cells. (b) Loss of myelin. (c) Infiltration of glial cells.