MRA Circle of willis non contrast scan!

Hi everyone, I was wondering if anyone else has been for a MRA Circle of Willis non contrast scan! I went for an indepth MRI on Thurs as my neurosurgeon has told me that I need an MVD on both sides. Initially I had been given my next apointment to see him on 2nd Oct but this morning I have received another letter asking me to go for an MRA circle of willis non contrast scan for the 6th Sept. This has got me a little worried now as I don't know why this has been requested the day after my MRI. Has anyone else has a similar experience and is this normal? My husband has rung the hospital and they have said that they just want to look in more detail but said they were unable to give the reasons as to why. I know that this can't have been further requested by my neurosurgeon at the moment as I am aaware that he is away on holiday!

Any thoughts or comments on this would be welcome!

Many thanks

Mandy