- Magnetic Resonance Spectroscopy (MRS)
- Diffusion Tensor Imaging (DTI)
- Functional Magnetic Resonance Imaging (fMRI)
Magnetic Resonance Spectroscopy or MRS is based on the principles of Nuclear Magnetic Resonance (NMR), and provides a means to non-invasively determine the relative quantification of metabolites in specific brain regions essentially allowing the ‘chemical sampling’ of the brain’s metabolites. Unlike MRI which uses the signal from protons to construct anatomical images, MRS determines metabolite concentrations and accordingly, data is not depicted as a reconstructed image but instead as a spectrum of relative metabolite concentrations.
MRS can be performed using a variety of nuclei including Phosphorus (31P), Carbon (13C), Sodium (23Na) and Hydrogen (1H). By far the most popular is hydrogen otherwise known as proton spectroscopy. This is partly due to the relative simplicity of the proton spectroscopy technique but also due to the natural abundance of protons in the brain that allows for greater spectral resolution. In MRS perhaps more so than other areas of MR, higher field strength offers significant advantages, particularly with respect to sensitivity and signal-to-noise ratio that ultimately results in more reliable spectra. The 3T GE scanner at the BMRI allows the measurement of metabolites that are pertinent to psychiatric and neurological research including gamma-amino butyric acid (GABA) and glutamate.
Diffusion Tensor Imaging or DTI together with tractography hold enormous potential when it comes to investigating in vivo neuroanatomy. The ability to investigate in vivo white matter connectivity completely non-invasively allows for unprecedented studies into brain connectivity.
Traditional MR imaging techniques that have been used to determine the functional implications of cerebral disease, have largely relied on the analysis of relationships to grey matter anatomy because of its readily identifiable contrast. White matter on the other hand is more opaque to routine imaging as a consequence of its less visible margins and more complex functional associations. Using conventional diffusion weighted MRI (which measures the rate at which water molecules diffuse in a specific direction) it is possible to reveal the brain’s underlying neuronal microstructure, normally “invisible” using conventional structural imaging. The DTI technique provides a method to estimate the paths followed by water as it diffuses within the white matter allowing the visualisation of the location, the orientation, and the anisotropy of the brain's white matter tracts.
Anatomical substrates such as cell membranes, myelin sheath as well as intracellular microorganelles all act as barriers to the diffusion of water thus influencing the spatial flow of these molecules. The architecture of the axons in parallel bundles and their myelin shield facilitates the diffusion of the water molecules along their main direction. When diffusion weighted images are acquired (in at least 6 non-collinear directions), it is possible to reconstruct a diffusion tensor and provide a 3D representation of the main diffusion direction. Using DTI techniques together with advanced fiber-tracking algorithms, it is possible to non-invasively construct 3D trajectories of neural tracts in-vivo, allowing the modelling of white matter neural connectivity.
Functional Magnetic Resonance Imaging or fMRI is an imaging technique that allows the in vivo investigation of the functional specialisation of discrete brain regions in networks that support psychological function. Functional MRI makes it possible to non-invasively obtain information relating to brain function at a much finer spatial resolution than any previous methods. The fMRI signal indirectly measures neural activity by localising the metabolic activity that follows, on the basis of changes in blood flow associated with mental activity, within the grey “thinking” matter of the brain where all the computations take place. Using fMRI, it is possible to ask questions regarding the neural basis of human behaviour. Functional MRI has experienced enormous growth in both the clinical as well as research domains and as a technique offers exciting opportunities to look into the workings of the brain.
The imaging facilities at the Brain and Mind Centre incorporate the latest software and hardware tools allowing sophisticated multimodal functional neuroimaging investigations. Support is also available for paradigm design and data analysis.