Neurodegenerative diseases are still diagnosed with respect to clinical scales, based on behavioral problems and the inner anguish they cause. Human brain imaging research reveals that these conditions are multifaceted, with different symptoms that can be traced to different networks of brain regions.
Brain imaging techniques allow doctors and researchers to view inside the human brain without invasive neurosurgery or administration of contrast agents. There are several accepted, safe-imaging techniques in use today in hospitals and research facilities throughout the world.
Diffusion MRI (dMRI)
dMRI is an MRI imaging method that produces in vivo images of the brain tissue weighted by the local microstructure characteristics of water diffusion. This diffusion process relates to the restricted diffusion of water molecules within the brain’s white matter.
The movement of water molecules is measured in different directions and the average diffusion ensemble is described by a spherical function, the so-called Orientation Distribution Function. Different quantitative measures can be extracted from these functions to characterize local tissue’s microscopic detail. Fractional anisotropy, for instance, describes how directionally dependent (i.e. how anisotropic) the diffusion ensemble is, enabling researchers to evaluate anatomical differences in brain regions.
fMRI provides rich information for assessing not only the volume and morphology of specific brain regions across developmental periods, but also the organization of these regions, allowing the description of fiber tracts within the brain. The reconstruction of the brain white matter fiber bundles, enables the evaluation of the complex anatomical connectivity patterns within the brain, and helps in characterizing (dis)connectivity basis of human cognition and its disorders (cerebral neoplasms, Parkinson’s disease, Alzheimer, Multiple Sclerosis, etc.).
Despite being painless and non-invasive, MRI scans can be unpleasant for those who are claustrophobic or otherwise uncomfortable with the device surrounding them.
Functional MRI (fMRI)
fMRI is a technique for measuring brain activity. It works by detecting the changes in blood oxygenation and flow that occurs in response to neural activity (named BOLD signal) – when an area of the brain is in use, blood flow to that region also increases. fMRI can be used to produce activation maps showing which parts of the brain are involved in a particular mental process.
However, fMRI doesn’t directly measure neuronal activity and the signal can be difficult to extract from the ‘noise’ of routine changes in blood flow, and the statistical techniques involved can be easily misunderstand or misused.