It's true that the investment does need to be recouped for purchasing future machines, but once you have one, it's a sunk cost.
And even then, if it's a big $5M machine [0] that lasts 10 years [1], and we generously assume it takes 1 hour per patient [2] and runs 12 hours a day, 300 days a year [3], the cost can be recouped if each test costs $140.
But an MRI bill easily costs 20 times the cost to recoup the investment.
[0]: They're usually $1-3M, and extremity scanners (hands, feet etc.) can be under $500k.
[1]: The average age of an MRI machine is ~11 years, i.e. they typically last 22 years
[2]: Most procedures take less than half an hour of scan time, but there's some shuffle and overhead
[3]: Medicine does not run on banker's hours