I expect MRI to be a high capex investment but low cost to run it each time. Maybe someone more knowledgeable might step in.
Of course, to play devil's advocate, using an MRI because you have it might lead to acquiring more MRI machines because of the high usage of the existing ones, I guess.
I used to do MRI experiments in grad school for neuroscience.
One time, I got curious, and did some back-of-the-envelope math on how much they cost. In NYC, an MRI machine drew as much energy in 20 minutes, as my apartment did in a month.
Between electricity, keeping a superconductor cool, and personnel costs, it cost ~$100/hr in a medical facility, 20 years ago.
I don't think there are all that many MRI machines that just sit there, unused, most of the day. There might be some hospitals that want to reserve their MRI machine for emergencies, so that it's less likely that you'll have to wait when you really need it.
Even though they name cost of operation, energy use, cost of spare parts, maintenance and repair as expenses for running an MRI. It looks to me like the biggest cost by far is going to be the acquisition and installation. So if you've invested in an MRI machine you probably want it to be in use as much as possible in order to recoup the cost of the machine.
Of course, to play devil's advocate, using an MRI because you have it might lead to acquiring more MRI machines because of the high usage of the existing ones, I guess.