Features
Canadian Medical Association Journal 1997; 156: 69-70
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© 1997 Michael OReilly
At the heart of the effort will be Canada's largest magnet, which was unveiled Sept. 30 when a new $6-million laboratory was opened at the Robarts Research Institute. The huge magnet, 1 of only 6 in the world, is the foundation for Canada's first dedicated functional magnetic resonance imaging (fMRI) machine. Functional MRI is a new technique that allows researchers to map not only the brain's anatomy but also its function. In effect, it allows researchers to see thought in action.
"This takes us into areas of human consciousness," explained Dr. Ravi Menon, a scientist at the institute. "We're able to look at human thought and emotions. We're now able to ask: What is thought, where is it in the brain and how does it function?"
The process known as fMRI was codeveloped in the early 1990s by Menon and fellow physicist Seiji Ogowa of the University of Minnesota. Instead of just imaging the anatomy, fMRI measures changing blood chemistry in real time. In this way it can "see" the body functioning.
For example, when a part of the brain is called into action, perhaps to move a finger or recall a memory, it demands more oxygen. As Ogowa discovered, deoxygenated blood has a different magnetic signature when compared with oxygenated blood. It is this difference that makes fMRI possible.
By measuring the differences between these 2 states, Menon can get a picture of brain activity while it is taking place. It is the same as the difference between a photograph of a highway and a video of the same road: the former shows what the road looks like, while the latter reveals how it is being used.
This technique has already been used to map the vital brain centres of neurosurgery patients. It has also been employed to study more esoteric questions, such as whether there is a "mind's eye." When thinking of an object, does one actually "see" it in the mind or is it imagined in a less-tangible way? The answer, according to Menon, is that the brain does indeed seem to "see."
"We were able to show that the same parts of the brain that are active [while something is being seen] are also working [when something is being imagined]," he explained.
The Robarts laboratory uses a 14 000-kg magnet with a field strength of 4 tesla to measure the minute magnetic changes in blood chemistry. A 4-tesla magnet is approximately 80 000 times stronger than Earth's magnetic field and nearly three times stronger than standard medical MRI machines.
"At 1.5 tesla you can see which side of the brain is dominant for language or what general area controls motor/visual functions," explained Menon. "With a 4-tesla [magnet] I can distinguish between centres that control the thumb and the index finger."
The institute paid almost $5 million for the state-of-the-art magnet, which it considers a bargain. "Siemens Medical Systems gave us an extremely good deal," said Jan Graves, the communications director.
Although only 6 of the powerful magnets exist, Menon says they are really little more than scaled-up versions of the type found in power tools and toy cars. Standard electromagnets are made by twisting copper wire around a metal bar. When an electric current is passed through the wire a north and south pole appear on the bar, and a magnet is created.
The same basic principle of physics is at work with the Robarts' magnet, although in this case the wire -- all 46 km of it -- is made of a superconducting niobium-tin alloy. It is supercooled to about 5 degrees above absolute zero using 2000 litres of liquid helium, which produces a superconducting wire that can maintain a current for years with no appreciable loss. This makes the magnetic field very stable.
This superconducting system keeps the current flowing evenly and produces the powerful magnetic fields that are opening up new areas of research through fMRI.