There seems to be a confusion here. MRI and CT scanners are entirely different machines, which operate in entirely different ways. CT scanners use X-rays from a source which is highly collimated to produce a narrow beam, which is rotated around the patient whilst moving along his body. This needs a fairly powerful x-ray source as most of the beam power is lost in the collimation process (basically a small hole through a large lead block). 50 kW or more to the source is not unreasonable, but this will be a high current at a relatively low voltage to produce fairly "soft" x-rays with a high intensity. Nearly all the energy will be lost in the collomator, otherwise the patient would suffer severe burns. As there are longish gaps between each scan, the cooling requirement on average would be fairly small because the collomator has a high thermal mass.

The MRI scanner uses a superconducting magnet, and this would need considerable cooling all the time, usually liquid helium is used and surrounded by chilled cooling to reduce the potential heat flow into the magnet. The rest of the operation does not use much power, and needs a discussion of quantum mechanics and advanced mathematics to understand.

David Stone said:

Nearly all the energy will be lost in the collomator, otherwise the patient would suffer severe burns.

Thank God for that! I recall being told in the dim and distant past that in the early days, the beam (for plain x-rays obviously) was focussed by feeling where it was warm.

David Stone said:

Nearly all the energy will be lost in the collomator, otherwise the patient would suffer severe burns.

Thank God for that! I recall being told in the dim and distant past that in the early days, the beam (for plain x-rays obviously) was focussed by feeling where it was warm.

Probably Chris, that could be true, but the x-ray tube would need to be running at thousands of Watts input because the conversion of electricity to X-rays is quite inefficient. The upside is of course that modern imaging machines are much more sensitive than the old film type. I will get some more info from my daughter, a radiologist dealing with Cancer patients. Treatment there is with 6-8 MeV X-rays from linear accelerators, very dangerous and exact dose and focus is critical.