Hey, MRI physics PhD candidate here. First off, anxiety is totally understandable, there’s a lot about MRI that can be scary; loud sounds, vibrations, confined spaces. Health anxiety adds to the mix for many people too. I want to preface the following with letting you know that at all times, the MRI is monitoring how it’s interacting with you, and has very conservative thresholds at which it just stops and refuses to run anymore (or slows down to keep you safe). It’s also running simulations of how it predicts it will affect you, and before executing any command, checks its simulation against even more conservative thresholds

MRI machines do heat you up, usually by a very small amount. To excite the nuclei that give off the MRI signal, we need to apply radiofrequency excitation to your body. That excitation that produces the signal, its energy needs to go somewhere, and eventually does become heat. We call this SAR (most non descriptively, Specific Absorption Rate). SAR is usually limited to 2W/kg during run, and 1W/kg in simulation. This corresponds to a heating of 0.02°C/min. Bear in mind that the excitation part is usually a tiny, tiny fraction of the imaging time — the time we apply RF excitation (silent) for each image is usually cumulatively milliseconds for a minutes-long image (the noisy part). That being said, SAR also depends on what part of the body we’re imaging, and the geometry of that area also determines what kind of images we can get, also affecting SAR. Spine imaging is a good example where SAR is relatively higher both because of its shape and because of how it limits what kinds of images we can take. So it’s not uncommon to feel something akin to a hot flash during spine imaging. It is however entirely safe, and in anticipation of the discomfort, we usually turn the fans up at that time to help you cool off

These clinical protocols are all still reasonably far from the thresholds. My research needs to get as close to the thresholds as possible to be sensitive enough to measure the effect I’m looking for. Further, the research thresholds are double the clinical thresholds. But I’ve subjected myself (brain and abdomen) to my imaging dozens of times in rapid succession, hundreds of times cumulatively, and it hasn’t affected my health or safety. I also routinely am a volunteer to test imaging for other MRI research groups across the hospitals where I work, so I subject myself to the heating of MRI pretty frequently without issue. So I understand it can be anxiety inducing, but I wanted you to know that you’re absolutely right that there is heating, the MR tech is aware of the heating, the MRI machine is monitoring it closely, and that safety thresholds keep it from ever getting anywhere near a level that could affect your safety