I had an MRI about 11 years ago for a rotator cuff tear in my left shoulder, the result of listening to a “body sculpting” instructor who believed that more push-ups were always a good thing and that all good athletes work through the pain. That MRI procedure was a nightmare for me. I mean, the techs were nice and understanding and all that. No one tortured me. No one stuck needles in me. No one repeated that common medical understatement, “This will cause some discomfort.” Still, I felt like I was in a plastic coffin. It made me feel like I wanted to claw my way out. I wanted to scream. Of course, with MRIs, the whole point is to stay still. That took all the willpower I could muster. I hadn’t realized that I would react with claustrophobia, so I had no pharmaceuticals to help, just the reassuring voice of the nurse in my headphones and the trope of counting down the remaining seconds in that contraption. Never again, I vowed.
Never say never. I have an MRI today at 1:30 p.m. Be there or be square.
So I put out this question to Google and the greater medical community: Why does today’s MRI have to be “closed”? Don’t they have newfangled “open” MRIs now? I swear I’ve seen ads for them in magazines and on the subway. I’m hoping the Valium helps, but still.
Getting to the answer to my selfish question requires a little background:
MRIs, like many of the technological marvels in our lives, resulted from a chance insight. In the 1880s, Nicola Tesla imagined the phenomenon of rotating magnetic fields. He first drew a diagram of it with a stick in the dirt. Even after he’d proved his idea and built a revolutionary induction motor with it, he couldn’t sell the concept in his native Europe, so he came to America to work for Thomas Edison.
Magnetic fields and electricity are inextricably bound. If I was a better physics student I could explain that more clearly, but trust me. So Tesla builds on the idea of rotating magnetic fields to create the idea of alternating electric current (what we know as AC). AC has many advantages over the direct current (DC) that Edison first developed: it can deliver charge in two directions, it can be transmitted more than two miles, it doesn’t have the unfortunate side effect of commonly causing overloads and fires. Edison doesn’t want to lose his DC empire, and he fights AC. Tesla eventually leaves Edison’s lab, and sells his 40-odd patents on the idea to Westinghouse. Our current “grid” of transmission lines, transformers and generating stations all operate on AC. Every time we switch on the lights, we should thank Tesla. I’m sure the Con Edison company does.
So, thirty years pass. In 1937, in a lab at Columbia University, a physicist discovers that, when exposed to a sufficiently strong magnetic field , the nuclei of cells will announce their presence. Usually, the billions of atoms in our bodies spin around randomly like woozy tops, the essence of controlled chaos. But when hit with a strong magnetic field and short, precisely-tuned radio waves, the nuclei of the atoms snap to a salute, all lining up like compass needles on a north-south axis. Then, when the machine gives the “at ease,” cells will briefly emit radio waves of their own as they return to their relaxed, chaotic state.
About forty more years go by. Then, a professor at SUNY Downstate Medical Center in Brooklyn, about 20 blocks south of where I’m writing this post, discovers that if you put cancerous tissue and normal tissue into a strong magnetic field, the two types of tissue will emit different kinds of radio waves. Essentially, each type of cell has its own radio handle. The intensity of the radio waves indicates how much tissue there is. The frequency of the waves makes it possible to identify the tissue. But this first use of magnetic resonance in medicine relies on a point-by-point body scan and the radio wave differences it measures don’t turn out to be useful in a making actual, consistent diagnoses.
But it got people in the field thinking. A professor at University of Illinois Champaign-Urbana generates the first MRI image by using “gradients,” three smaller magnets within the main magnet. When these gradient magnets are turned off and on very quickly, they can alter the larger magnetic field on a local level. That makes it possible to take a picture of exactly what the doctors want to see, in both two dimensions and three dimensions. Still, these scans took hours and hours.
Then, a professor at the University of Nottingham in the UK, developed a mathematical technique of translating the tissue radiowaves into images. Suddenly, it was possible to use the rotating magnetic fields, the gradient magents, the radio waves and supercomputers to generate pictures of almost unbelievable clarity, and to do it in minutes, rather than hours. The first full body MRI scan was done in 1977, when I was 14.
So what does this mean for today? The MRI machine that will take pictures of my breasts will be able to take pictures in three dimensions. It will be able to make images that are “slices” of my breast in any orientation: horizontal, vertical, and any angle in between. It allows my doctors to ask very specific questions and get very specific answers.
They’ll be looking for hydrogen atoms. As we all learned in elementary school, our bodies are mostly water, H2O. That’s a lot of hydrogen. The protons in my hydrogen atoms will be saluting and relaxing furiously. Cancerous tissue, it turns out, has more water than regular tissue. In an MRI, it emits a slightly longer radio signal. Cancer is sneaky, but in an MRI, it shouts its name.
So why can’t I do an open MRI? Apparently, open MRIs are best for folks who are having scans of extremities—knees, elbows and such—or who are too large to fit in a regular MRI, which is too small for anyone who weighs more than 300 pounds. (Woo-hoo! I’m thin!) Instead of a tube through a big block, open MRIs look like a gantry, two thick, cylindrical disks, one above, and one below, the patient. Apparently, the kind of scan I’m having requires a magnetic field that’s almost unimaginably strong. Open MRIs don’t seem to have the oomph for what I need.
Magnetic fields are measured in either “Tesla” (a nod to the brilliant Serbian) or in “Gauss” (for Carl Friedrich Gauss, a German polymath who first described the inner and outer sources of the Earth’s magnetic field). Our planet’s magnetic field measures .5 Tesla or 5,000 Gauss. Regular MRI machines create magnetic fields of .5 to 2 Tesla, the limit approved for medical scans. In lab research, though, magnets of up to 60 Tesla are used. Take that, refrigerator magnets.
OK, so I need a big magnetic field. Why the tube? There are several types of magnets:
• One kind is called a resistive magnet, coils of wire wrapped around a tube, or “bore.” Shoot an electric current through the coils, and voilá, you’ve got a magnet. But creating a large enough field for my MRI would take 50 kilowatts of electricity, quite a lot. That sort of electric bill would suck the life out of any medical center’s endowment, not to mention creating a huge carbon footprint.
• Another kind of magnet is called a permanent magnet, kind of like your science kit magnet, but much, much larger. A permanent magnet large enough for an MRI would weigh many, many tons. The floor would have to be super-reinforced so that the thing wouldn’t drop through the building into the subway. Plus, permanent magnets usually can’t create fields as strong as 2 Tesla. The smaller the magnetic field, the less clear the images. While the American Cancer Society three years ago recommended MRIs for women who have breast cancer, or who are at risk of developing it, MRIs yield a lot of “false positives,” that is, images that look like cancer but then turn out not to be. I’m all for clear images.
• The third kind of magnet, a superconducting magnet, is the technical workaround that make modern MRI scans practically feasible. Turns out that if the coils of a resistive magnet are made really, really cold, the resistance in the metal coils drops to near zero, and the brings down the power required to create the magnetic field. So, in an MRI, the coils are bathed in liquid helium, at 452.4 degrees below zero. The coils and the helium are then insulated by a vacuum, akin to a giant Thermos.
All of this marvel must reside in a giant plastic housing, probably 7 feet by 7 feet by 10 feet. If a the machine is a bit newer, then it may only be 6 feet long, which may help my claustrophobia a bit. I and my breasts have to lie in the center of the magnetic field, or the magent’s “bore.” That way, my hydrogen atoms will do their north-south salute in the direction of the tube. Surrounded by metal coils, liquid helium and connected to a computer that does unimaginable voodoo math, that is where I’ll get to enjoy my Valium.
Around the bore, is a magnet, or perhaps it would be more accurate to say, a MAGNET.
The machine probably has a price tag of at least $1 million. Thank you military-industrial complex. Thank you cancer center donors.