Your MRI may be a double MRI. They do a standard MRI then do an MRI where they remove the images of blood. When they subtract the second image from the first, they get a image of the vascular structures.

In an MRI of the head, you lay on the bed with a cage over your head. The cage is the image gathering device. I've had three of these. No big deal. I'm claustrophobic so I close my eyes before going into the tunnel. I also hold my elbows close in so they do not touch the side of the tunnel.