The doctor is not "losing" $450. MRIs are vastly overpriced on a routine basis. If you had to pay the whole $1650 instead of $350 you would shop around. Then you would discover that you could get the same MRI for a fraction of the cost.
Let's assess how the original charge is arrived at, shall we?
Cost of scanner: 1.5 - 2 million $
Place to put scanner (facility build out, rental, compliance with reams of regulations): 500K
Tech to run scanner + benefits: 150K.
Nurse to start IVs and sedate claustrophobic pt + benefits: 200K
Service contract to maintain scanner: 50-100k/yr
Clerical staff+ benefits: 100K
IT infrastructure for interpretation and reporting: 200K
Malpractice/liability insurance: 100K/yr
Radiologist salary: $300K/yr
Housekeeping services: 50K/yr
Utility charges: 10k/yr (?)
You might want to rethink your original statement.