This is always extra annoying because it might be a false savings to pay cash there. Let's say your MRI says you need a $5500 procedure, and your plan's deductible is $3000, 90% coverage after, and out of pocket max is $6000, and there's nothing else you've spent on the plan this year.
Pay $800 for MRI with insurance, you'll then pay $2200 for the procedure to hit the deductible + 10% of the remaining $3300, so $2530 total for the procedure. $3330 total for the year between the two things.
Pay $600 cash for MRI, you'll then pay $3000 for the procedure to hit the deductible, and 10% of the remaining $2000, so $3200 total for the procedure. Now you've paid $3800 total, so you've spent $470 more despite the MRI being "cheaper"!
If you have other expenses so your out of pocket max comes into play, that difference approaches the full $600.
Pay $800 for MRI with insurance, you'll then pay $2200 for the procedure to hit the deductible + 10% of the remaining $3300, so $2530 total for the procedure. $3330 total for the year between the two things.
Pay $600 cash for MRI, you'll then pay $3000 for the procedure to hit the deductible, and 10% of the remaining $2000, so $3200 total for the procedure. Now you've paid $3800 total, so you've spent $470 more despite the MRI being "cheaper"!
If you have other expenses so your out of pocket max comes into play, that difference approaches the full $600.