Diffusion imaging is based on analyzing the movements of water molecules in a tissue. The parameter measuring the intensity of this diffusion is the apparent coefficient of diffusion (ADC) which varies in particular as a function of the cell density. Diffusion imaging is therefore a modality that reflects tissue density, and in this case is capable of revealing pathological processes in white matter.
Diffusion tensor imaging (DTI), a newer and complementary modality, allows estimation of the preferred directions of diffusion of water molecules in a tissue.
Compared to "single" scattering imaging that uses scattering gradients applied in 3 directions, DTI uses these same gradients applied in at least 6 directions (20 for our study).
In white matter, diffusion is constrained by the axon cell membrane and the myelin sheath, and preferably follows the fiber bundles tangentially. Diffusion tensor modeling allows the determination within a voxel of the principal direction (maximum diffusivity) of proton motion, which corresponds to the orientation of the white matter fibers.
Thus, DTI allows the study of tissue microstructural organization. This degree of organization of SB is measurable through diffusion tensor parameters, such as the fraction of anisotropy or fractional anisotropy (FA). When the diffusion is constrained in a main direction, it is said to be anisotropic and the FA tends towards 1. On the other hand, when it is carried out indifferently in all directions of space, it is said to be isotropic and the FA then tends towards a zero value.
It would appear, therefore, that DTI may be a more sensitive means than diffusion for revealing apparently normal SB abnormalities related to head trauma
For patients who have a concussion, doctors in the sports medicine department will offer them MRI after the visit. At this visit, the investigator will inform (orally and in writing) the subject about the study and, after obtaining the subject's consent, note demographic and clinical information, date of concussion, complications, medical history and SCAT 5 (standardized tool for concussions) score. After the inclusion and exclusion criteria have been verified, the participant will be invited within 7 days to perform an MRI.
For control subjects, following presentation of the study by one of the investigators, they will be summoned for the baseline visit followed by the first MRI. The 15-minute baseline visit will be conducted by one of the study investigators. The investigator will inform (orally and in writing) the subject about the study and after obtaining their consent will record demographic information, medical history and check inclusion and exclusion criteria. MRI will be done next.
After a delay of 1 month ± 5 days, the second MRI will be scheduled for all subjects.
The first MRI consists of several sequences (the total acquisition time is less than one hour) (no contrast injection for these tests). The second is shorter and involves the acquisition of the sequence in diffusion voltage (7 minutes) and that of anatomical locating images (4 minutes).
