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Neurology Now:
Brain Imaging: Special Section

Searching for a Powerful Sharper Image: Powerful MRI can spot tumors, aneurysms and mini‐strokes, but can't yet reveal if the author's brain will bleed again

Valeo, Tom

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Tom Valeo is a science and medical writer whose articles have appeared in Scientific American and WebMD.

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Abstract

A fuzzy white dot on the MRI demonstrated that the tingling in my right arm was caused by bleeding in my brain stem. A tiny tangle of capillaries known as an angioma had started to leak, and the blood was pressing against surrounding neurons, producing the classic symptoms of a stroke.

Without the MRI, my doctors might have concluded that a clot was blocking an artery somewhere in my brain. They might have given me a blood thinner, which would have made the bleeding worse. By revealing an angioma no larger than a grain of rice, the MRI may have saved me from paralysis, or worse.

Now, however, such an amazing image is not good enough for me. The angioma that bled may have withered and disappeared.

Or it may be about to bleed again, this time with catastrophic results. The machine that revealed my angioma is not powerful enough to tell me if it's still there. That means I may be fine, or I may be on the brink of disaster.

Only time will tell — or a more powerful MRI.

The brain stem is a tight cord, no larger than a man's thumb, containing the neurons that link the brain to the rest of the body. The bleeding in my brain stem disrupted the neurons running to my right arm and the right side of my face. The tingling in my arm disappeared in less than 24 hours, but sensation on the right side of my face remains deranged. Sunlight feels cold, for example, while wind feels hot.

Another bleed could paralyze my arm, the right side of my face, or some other part of my body. A severe bleed in the brain stem could produce what's known as “locked-in syndrome” — total paralysis of all muscles in the body, except for the eyelids.

If that angioma is still in my brain stem, I would take drastic action to prevent another bleed. I would keep my blood pressure as low as possible, for example, and avoid any activity — even bending over — that would encourage blood to rush to my head.

If I knew the angioma was gone, I could relax.

And it might be gone. Coincidentally, my neurologist had an angioma rupture in his own brain when he was 14. The bleeding left him unable to speak and numb on one side of his body. Over many months he recovered, and subsequent MRI scans found no trace of the angioma, leading him to believe that the capsule containing the tiny arteries withered and disappeared after the bleed.

That may have happened to me too, he thinks, and I desperately want to believe him, but we can't know for sure unless I find an MRI scanner that can produce extremely sharp and detailed images. For that, I must wait.

MRI scanners are in the midst of an awkward adolescence. They've grown strong, sleek and sophisticated since 1977, when Raymond Damadian made the first crude picture of the inside of a human using what came to be known as magnetic resonance imaging.

Today the MRI produces images that would have astonished physicians 30 years ago. Tiny strokes, so small that even an autopsy might fail to detect them, are readily visible on an MRI. A dangerously ballooning aneurysm will stand out clearly. Small tumors, the lesions of multiple sclerosis, damage caused by Alzheimer's disease — all these problems would be detected easily by any of the approximately 8,000 MRI scanners currently available in the United States. A functional MRI, or fMRI, can even show the brain at work by monitoring how much oxygen various tissues consume while performing some mental task.

But MRIs will grow much stronger in the years ahead. They will produce images sharp enough to reveal capillaries, neurons and other microscopic details. Experimental machines already built can actually reveal the vein that passes through an MS lesion — an object no wider than a human hair.

The MRI scanner works by surrounding the patient with an extremely powerful magnetic field measured in a unit known as a tesla, which is 20,000 times greater than the Earth's magnetic field. This magnet causes all the protons in the body to line up in the same direction. Then a coil fires radiofrequency waves at the part of the body being examined. These waves cause the protons to wobble and give off a signal that is captured and sent to a computer, which builds an image out of the information.Many MRIs already have a magnetic field of 3 teslas, which is the strongest allowed by the Food and Drug Administration for clinical use. That's twice as powerful as the one used to examine my brain, but probably not strong enough to reveal what I need to see. An 8-tesla machine, which my neurologist calls “Buck Rogers technology,” was built in 1998 at Ohio State University, and 9.4-tesla units have been constructed at the University of Minnesota and the University of Illinois—Chicago.

These machines, known as “ultra high-field MRIs,” have brought radical improvements in resolution and image quality, and will get better yet, according Pierre-Marie L. Robitaille, Ph.D., the radiology professor who designed Ohio State's 8-tesla unit. But they will hit a technological limit at about 11.75 teslas, he predicts, because magnets that strong will have to be wound with wire containing niobium and tin, which produce a brittle alloy. As a result, MRIs beyond 12 teslas would be extraordinarily expensive to build.

Figure. Though barel...
Figure. Though barel...
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“At some point it becomes so expensive that building it becomes an ethical question,” Dr. Robitaille says. “Should you concentrate all this wealth in an instrument to serve a few people, or should you build many less powerful machines that would help many more human beings?”

So why don't I have an MRI done by one of these powerful machines already in existence? Surely they could produce an image clear enough to determine if the angioma in my brain stem is still there.

Alas, while such machines produce spectacular images of the upper part of the brain, they apparently can't see the brain stem very well, according to Kottil Rammohan, M.D., director of clinical and experimental neuroimmunology at Ohio State University Medical Center.

Figure. DIGITAL DETA...
Figure. DIGITAL DETA...
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‘When you get to the lower part of the brain, there's so much more bone in close proximity to the brain,” says Dr. Rammohan. “You cannot use the 8-tesla machine to image the spinal cord either. It's a limitation of the technology.”

It could be done, according to Dr. Robitaille, “but we'd probably have to build specialized coils to get that image.”

So I must wait. In the meantime I can't be sure if the occasional tingling on the right side of my face is caused by nerve damage from the original bleed, or new blood oozing from the same angioma.

Only a high-resolution image of my brain stem produced by an MRI not yet available will tell me what I long to know.

©2006 American Academy of Neurology

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