MRI: A Guided Tour
Table of Contents
By Kristen Coyne
"Darn this aching back!”
That about sums up your thoughts as, flat on your back, clad in a thin hospital gown, you are guided into a dark, tunnel-like tube, a kind of medical solitary confinement where you’ll be spending the next 30 to 60 minutes. Your ears are stuffed with plugs, sound-cancelling headphones cradle your cranium, your extremities are stripped of watch, jewelry and other sentimental comforts, and you may feel a touch of claustrophobia. And it’s all because your orthopedist, worried about that chronic ache in your back, ordered an MRI scan.
Look on the bright side: MRI scans sure beat surgery, which was your only option 20-some years ago, before MRI became a routine, highly-valued diagnostic tool for doctors. In fact, when you take time to think about it, these machines are pretty amazing. And because you’ll be a captive audience while the technologist in the next room takes a bunch of fancy photos of your spine, we suggest you relax and let us tell you the story of the remarkable contraption in which you are, for the time being at least, stuck. We suggest you think of the cylinder as a kind of spacesuit, the machine as a spaceship, and you as an astronaut about to embark on a journey to the center of ... your body!
You probably already have a vague idea of what’s going on. MRI – doesn’t that stand for Magnetic Resonance Imaging? Bull’s-eye. But what does that mean, exactly? Some type of X-ray, isn’t it?
Close, but not quite. MRI scanners, like X-rays and CT scanners, are basically machines doctors use to take pictures of your insides so that they can figure out what’s ailing you. But MRI doesn’t involve ionizing radiation, as do X-rays and CT scans. Rather, MRI takes advantage of something you have plenty of in your body: water. It is far more flexible than X-rays and CT scans, and can generate three dimensional images in any orientation and at any depth in the body.
PHYSICS FACTOID: In research and industry, MRI is known as NMR – nuclear magnetic resonance. It's more or less the same process, but the medical establishment prefers the term MRI because some patients are scared off by the word nuclear.
The upshot is that MRI, for most applications, is far superior to other imaging tools in providing non-invasive images (and even chemical information) at high resolution. That’s why hospitals pay millions of dollars for the multi-ton behemoths, and spend hundreds of thousands more a year operating them. Since 1977, when the first MRI exam was conducted on a person, the procedure has become quite common. In 2003, some 60 million scans were performed using about 10,000 MRI scanners worldwide.
While X-rays remain useful for looking at bones, MRI scans are the diagnostic tool of choice for soft tissue – organs, ligaments, the circulatory system and (as you know) the spinal column and cord. They help physicians identify multiple sclerosis, tumors, tendonitis, strokes and many other conditions. What’s more, MRI technology is still in its infancy. Manufacturers are constantly improving scanner designs, and scientists are discovering new applications, from monitoring wine quality to detecting lies; one MRI study revealed that people used twice as many regions of the brain to tell lies as they did to tell the truth.
We know a lot about MRIs at the MagLab because we have the world's strongest MRI scanner: Our 900 MHz nuclear magnetic resonance magnet produces a magnetic field of 21.1 tesla. As you'll soon read, that's far stronger than a hospital MRI scanner. We can't fit humans in it, just laboratory animals such as mice and rats. But the MRI research done on those animals is helping scientists understand a wide variety of human disorders, from Alzheimer's to cancer to muscle degeneration.
We have a lot of ground to cover in describing how MRI works. In the pages ahead, we’ll learn about the secret lives of hydrogen atoms, how radio waves can make you flip, and facts about superconductivity that will send shivers down your sore spine. It’s all fascinating, but try not to get too excited – you’ll blur your MRI scans!
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