Bright spots & black holes: what doctors are learning from advanced MRI

Inside MS, Oct-Dec, 2002 by Martha King

What doctors are learning is not comfortable news. We present the technical details for those of you who want to know how these techniques apply to understanding MS.

The bottom line is brief: uncontrolled MS damages the central nervous system--the brain and spinal cord--and for many people the damage will, in time, be permanent. The fatty material that protects nerve fibers (myelin)is destroyed and replaced by scarring; and so, it turns out, is some gray matter (nerve cells as well as the nerve-cell fibers, or axons). Black holes and overall shrinkage of the brain, called atrophy, may occur. The sooner disease-modifying therapy is begun, the more effectively this damage can be delayed or prevented.

In other words, new findings confirm the wisdom of the National MS Society Consensus on Disease Management, issued in 1998. We urge you to discuss this with your persona physician and to reach out for counseling and support by contacting your Society chapter.

Fifty years ago, MRI was called NMR. The letters stood for "nuclear magnetic resonance" and it was used in laboratory research. Then, late in the 1970s, as computer technology improved, NMR was enlarged, modified--and renamed. The developers were skittish about trying to persuade people to use a medical imaging device with the word "nuclear" in it. The name "magnetic resonance imaging" was adopted.

The basic technology didn't change. Then and now, there is no radiation or nuclear energy involved in MRI. It uses radio waves and magnetism.

A strong magnetic field makes the hydrogen protons in water molecules line up; then radio waves knock the protons out of line. When the radio waves are stopped, the protons relax back into line, releasing "resonance" signals, which are transmitted to a computer. Fancy computer programs convert these data into a picture--of water. The water in living human tissues.

Where fat isn't, water is

Because the myelin layer that protects nerve-cell fibers is fatty, it repels water. Thus, MS damage reveals itself on MRI because areas that are stripped of fatty myelin hold more water. MS lesions, or damaged areas, show up as bright spots.

Early in the 1980s, the first serial MRI scans of people with MS changed physicians' fundamental understanding of this disease forever. Those pioneering MRI studies revealed that MS is a constantly active on-going disease from the very beginning.

Even when a person with MS is in remission and feels well, events are taking place in the brain or spinal cord. Some MS doctors call these events "explosions in the brain." MRI studies demonstrate that they happen five to ten times more frequently than visible MS relapses or attacks.

A reliable measurement

Today, MRI is an essential measure of MS activity. Researchers can count the number and measure the size of lesions, and that gives them an objective measure of multiple sclerosis activity. In a slow-moving, notoriously variable illness like MS, researchers had been hard-pressed to find a benchmark for evaluating the effect of treatments. MRI data are simple: smaller and fewer lesions = good; more and larger lesions = bad.

The big glitch is the lack of clear correlation between the MRI picture of MS and the clinical picture of MS--which is how a person feels or acts in daily life. But as MRI technology has marched forward, it has become more and more clear why fewer and smaller lesions = good. Over a longer term, the total extent of damage seen on MRI is definitely related to a person's disability. Indeed, some of the cognitive problems people have--with memory, word-finding, or problem-solving--have now been linked to the location of lesions as well as to their number and size.

"Gadolinium enhancement" sees active inflammation

Gadolinium is a contrast agent. Infused into the bloodstream a few minutes before an MRI, it lights up areas where immune-system cells are leaking out of tiny blood vessels and into the central nervous system. This is a hallmark of active inflammation, a key event in the MS attack on myelin. (Normally, immune cells are kept away from brain tissues by the blood-brain barrier, a layer of specialized cells inside capillary walls.)

Studies show that a gadolinium-enhancing lesion lights up for three to six weeks and then fades. Thus these scans are indicators of active disease during the preceding 45 days or so.

Unfortunately, fading doesn't always mean a lesion has fixed itself and disappeared. It may remain on a "T2 weighted" MRI scan.

T2 weighted scans give a good one-year look back

The MRI computer program can produce pictures based on two different proton relaxation times, called T1 and T2 weighted scans. The T2 scans reflect the level of disease activity in the preceding year. The lesions these scans reveal continue to show up as high-water bright spots after the gadolinium enhancements have gone away. They are referred to as plaques. Occasionally lesions repair themselves and disappear forever. Others reinflame later on, sometimes again and again. Over time, scientists have learned, repeated inflammation changes their nature altogether.