What Should Be The Ideal Time For Stop Feeding?

Hi. I have a 1.6 year old daughter who was born at 27 weeks with hydrocrphalus. She had been shunted a year back. Her doctor has now advised for an MRI for the brain. I would like to know the approximate cost and about the procedure of MRI so that I can go prepared. WIll she require to be sedated? How long? When should I stop her feeds, if she needs to be sedated? Thanks