Taking a numerical approach to fMRI
15 Mar 2012 by Evoluted New Media
Functional magnetic resonance imaging only gives us a glimpse of what’s going on in the brain. Researchers from the University of Oxford have modified the technique to provide a full numerical measure of how the brain is working.
fMRI produces pictures of the working brain by showing areas which light up when certain tasks are being performed, but the technique only captures relative changes in the MR signal. The signal reflects a complex mix of different physiological processes in the brain – it is very much an indirect indicator of activity.
“MRI is great for localising which areas of the brain are activated during different stimuli and so helping us to understand how the brain works as a whole,” said Dr Daniel Bulte from the Centre for Functional Magnetic Imaging of the Brain (FBRIB). “However the images we produce are just that, pictures. They are not measurements.”
So researchers have modified the technique: patients lie in the MRI scanner and breathe air though a mask or tube. The proportion of carbon dioxide and oxygen are varied slightly, which enabled researchers to use the MRI signal to measure blood flow, blood volume, oxygen use and brain metabolism across the whole brain.
“By making some slight changes to the air breathed by a patient in the scanner we can produce beautiful images of brain physiology that actually correspond to real measurements,” said Bulte, who published his findings in NeuroImage.
The measurements obtained are comparable to those using a more complex medical technique –Oxygen-15 positron emission tomography. However, this technique is costly, and only available in limited areas of the world. It also exposes patients to radioactive labels.
Bulte says the new technique takes less than 20 minutes to perform and could be run on any modern clinical MRI scanner. It is also cheap and uses no drugs or injections.
The technique could be used to provide clinically useful information about patients coming to hospitals with strokes, brain injuries and a variety of other conditions.
