life

MRIs and headlights

Sun, 2010-10-31 14:08

This week I had my annual abdominal MRI. It went well, despite some anxiety that I was feeling leading up to it. You see, the way it works is I lie down on a narrow table. Technicians strap me to it, and start an IV in my arm (sometimes in my hand). They put large headphones on my ears, which muffles a lot of sound, and then the table slides into a tube with me on it. The tube is narrow, so there is only a few inches of space in front of my face. I close my eyes and keep them closed the whole time I am in the tube. Through the headphones, the technicians speak to me. The only thing I ever have to do is hold my breath. Periodically, I hear them say things like, "For the next one, you will hold your breath for 15 seconds. Hold your breath!" and I inhale and hold my breath. Then there is a repeating series of loud sounds, often like an alarm. The sound is the most surprising thing about MRIs: they are quite varied, and quite loud. From wikipedia:

Switching of field gradients causes a change in the Lorentz force experienced by the gradient coils, producing minute expansions and contractions of the coil itself. As the switching is typically in the audible frequency range, the resulting vibration produces loud noises (clicking or beeping). This is most marked with high-field machines[42] and rapid-imaging techniques in which sound intensity can reach 120 dB(A) (equivalent to a jet engine at take-off),[43] and therefore appropriate ear protection is essential for anyone inside the MRI scanner room during the examination.

I don't think the MRIs I get are quite that loud, but still they always make me laugh: it all seems like a test to see if they can make me stop holding my breath via noises.

In between the breath holding bits, there are long pauses when I don't have to do anything. In these bits, I sometimes get a little claustrophobic, but never badly. I can feel that my feet are outside of the tube, and that always helps. Last year, I did a visualization in which I imagined I was on a luge run on a sunny day (there is always a fair amount of light in the tube). It was hard to imagine the turns, but still it gave me something to do. This time, I found I didn't need to do any visualizations: I felt quite comfortable the whole time.

At the end of the time in the tube, they use the IV to inject a dye. I can feel it moving into my arm, and sometimes feel it in my arm, or my hand. Last year, when I held my breath after the dye went in, I got a very strange sensation in my chest. This freaked me out a bit, but it only lasted a few seconds. I mentioned it to the technician (there is a microphone in the tube) and they said that was normal. This time I didn't feel anything like that at all.

Overall, a pleasant and interesting experience.

In other news, I bought myself a headlight for my bike. I already had two full-blown headlights, plus a little backup one, but they are old or bulky or don't work well with the larger diameter of my modern handlebars. So, I got a Light and Motion Stella 300. I wanted a single headlight, with a battery I could mount under my stem, all slick-like. So far, on one 90 minute ride last week, it has proven itself to be awesome!