Magnetic Resonance Imaging: An Introduction
Magnetic Resonance Imagine (MRI) is a commonly used tool for imaging the body. It works by generating a strong magnetic field, which causes the protons in the body to align in the same direction. Then, a radio wave knocks the protons out of alignment. The speed at which the protons return to being aligned with the magnetic field is indicative of the type of tissue in that area of the body. By measuring this, we can get a good idea of which areas are white matter, grey matter, and fluid-filled ventricles. The strength of the magnetic field is measured in Teslas (T), and a typical scanner used for medical purposes will have a field between 0.2 and 3 T.
Research uses for MRI
A primary use for MRI in neurological research is to acquire images of the anatomy of a subject's brain. However, another widely used method is to use MRI to acquire functional images (fMRI), in order to visualize the processes occuring in the brain. Rather than examining the protons in the brain, the signal is instead gathered from hemoglobin, allowing the blood flow in the brain to be measured. While the exact relationship between neural activity and blood flow is not known, they are strongly correlated, and as such the fMRI signal is assumed to be related to the activity of the brain.
MRI at the Montreal Neurological Institute
The Speech Motor Control Lab has access to two MRI scanners, housed at the Montreal Neurological Institute (MNI). The two scanners, a 1.5 T Siemens Sonata and a 3 T Siemens Trio, are dedicated for research use. The facilities include audiovisual equipment for stimulus presentation, and the scanners are operated by trained MRI Technologists.