CAT, PET, MRI

Tomography, is literally any "image slicing" technique (to make 3Ds from 2D slices),and for this always requires a machine like a big donut, whether CAT, PET, or MRI.  CAT and PET are just donut detectors. MRI's donut also hides a superconducting magnetic coil.

CATs use X-rays and got their name because they were the first to Compute their Axial Tomography, so they got the cool name to differentiate from flat plate X-rays (which was just about the only "radiology" back then). That spinning noise is you hear (when in them) is the x-ray emitter and x-ray detector (180deg apart) chasing each other around the donut.

MRI uses magnetic resonance (magneto-radio stuff) and hums harmonically while imaging, and the cryo-pumps sound like tropical birds.

PET uses positrons (antimatter electrons; an electron-sized particle with a positive charge) from a decaying radioactive tracer, but since antimatter quickly annihilates when it hits matter, the detectors detect one of a pair of gamma rays that result from the annihilation. It is really about picking the tracer for what you want to "see happening". I'm pretty sure this means that the PET machine is just a passive camera, and all the radiation used will be actually coming entirely from tracers injected *inside* me and not beamed in by the machine (CAT uses a mix of x-rays beamed through and tracers radiating out)

Wikipedia on PET & Oncology

Flourine 18 gets drawn into cells with high glucose uptake (the brain, liver & cancers), then gets stuck, then decays, emitting its positron, triggering the gamma rays that say "glucose is being drawn here" (thus calling out the cancers).

By the way, my current diet is near-zero carb, no milk or red meat, and low protein (aka high fish, eggs, nuts & oils) so as to starve the bad guys of the glucose they crave. Brains hare happy switching to ketosis (burning fats), but cancer is dumb and just wants the sugar.