If you ever get cancer... Maybe it's just that I lucked into getting the most aggressive oncologists, but on more than one occasion I was sent to get an MRI or CT on the spur of the moment. There were times when it was scheduled out as well - but along the lines of "come back in six months; we'll schedule the CT for the week before".

(But I know I was lucky - my oncologist could order a river to reverse itself and it probably would.)