| Last time I had an MRI scan, I had strong sensations throughout my body where exposed to the MRI's radio emissions. I rather enjoyed the sensation, it felt like a massage and I would have enjoyed it for longer. I was surprised, as they didn't mention this before the scan. After, I asked about it, and they told me most people don't feel anything, but some do like me, and for a few it's so painful they have to stop the scan. They told me it was my peripheral nervous system interacting with the radio emissions, not a physical (non-signal) effect as it felt like. From that conversation I learned there was about 10kW transmitted through my body during the scan. MRIs have been studied for dangerous effects, of course, and all the evidence shows them to be extremely safe... provided there is no metal in the body which can heat up or be displaced by the field, and not counting risks from the contrast agents which are sometimes injected, which some people are more susceptible to than others. I was never convinced by dismissive arguments that non-ionising radiation "can't" have any biological effect other than localised heating, or that the thermal background spectrum means infrared and below can't have an effect. (I know the physics pretty well; it's not lack of understanding.) But after those sensations caused directly by the emissions, I'd experienced a biological, non-thermal effect from radio in the microwave-or-below frequency range directly and clearly. That was really interesting. The body clearly does a lot of things based on countless subtle signalling pathways. Pretty much anything any pathway can sense could have an effect, even if it's not a conventional chemical reaction. One of the more interesting technological ideas around this is the use of high coherence terahertz signals that resonate with DNA molecular dynamics. |
THz radiation is a different story too as it has about enough energy such that it could influence irreversible processes.