An MRCP simply put is an MRI that consentrates on the bile ducts of your liver. It's done exactly the same way a regular MRI is. I had one done about 2 years ago when I also had elevated liver enzynes appear in my bloodwork. Having UC makes us "canidates" for liver, gallbladder problems. Your Dr. may be checking to see if you have developed PSC (Primary Sclerosing Cholangitis). Which is narrowing or blockage of your bile ducts. If you google it there is plenty of info on this. Hope all goes well.
FYI an MRCP is a very easy test an completely painless. Just think of it as an MRI.