Michael D. Noseworthy
Department Electrical and Computer Engineering
McMaster University

Correlating brain structure with function using magnetic resonance.

Magnetic resonance imaging (MRI) is a well known and popular technique for non-invasive imaging of the human body. Through use of a large magnetic field in conjunction with pulses of radiowaves, MRI provides high resolution images with spectacular clarity and detail. A plethora of scan types are available on an MRI system that can now allow visualization of brain microstructure at sub-millimeter resolution with high signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). A host of these specialized brain scans can allow one to probe microvascular structure and tracts of myelinated fibers. In addition sub-millimeter deposits of iron and calcium can be observed, both of which are linked to numerous brain pathologies. Diffusion sensitized MRI, in combination with a post-processing algorithm called tractography, can be used to visualize brain microfiber connectivity. In parallel to development of these advanced capabilities in structural imaging, advances in the MRI system have also focused on the probing of brain tissue function and metabolism. The most popular and simplest example of this wide breadth of applied MRI is functional MRI (fMRI), which probes the increased oxy:deoxy haemoglobin ratio that results when the brain is 'activated'. The fMRI technique allows quantification and spatial localization of brain activation during a host of simple to complex tasks.  Furthermore, in vivo nuclear magnetic resonance (NMR), better known in the radiological world as magnetic resonance spectroscopy (MRS) can also be performed using many types of MRI systems. This technique allows one to directly probe the biochemical and metabolic makeup of the brain. Proton, or hydrogen (1H) MRS has become popular in clinical brain scanning to aid in evaluating numerous brain problems including hypoxia, tumour characterization, and demyelination (to name only a few). In addition this technique can be use to quantify some neurotransmitters (e.g. GABA, glutamate, glutatmine), and even some pharmaceuticals in brain tissue. Few realize, however, that this spectroscopic method is not limited to probing only molecules with 1H nuclei. Any atomic nucleus having the quantum mechanical property 'spin', which exists biologically at a large enough and freely mobile concentration, can in theory be imaged with multinuclear MRS. Some biologically relevant nuclei include carbon (13C), fluorine (19F), sodium (23Na), and phosphorous (31P). It should be noted that these are all naturally occurring isotopes and thus there is no need to inject any radioactivity. With a host of available nuclei for MRS evaluation of the brain the assessment of neurodegenerative diseases, mood disorders, cancer therapies, and metabolic disorders, to name a few, has become easier and safer.  In this talk I will present an overview of new structural and MRS imaging technologies that allow the combined assessment of both structure and function for the study of healthy and diseased brain.