Dear patient, you have had an anaphylactic reaction, i.e., a severe formof allergic reaction due to the contrast of the MRI. mild rash at injection sit could be managed with antiallergic drugs like cetrizine, but bleeding in urine/ stools is a sign of severe reaction and u need additional medictions and medical care. i would best advice you to visit an ER at the earliest. And also, keep a record of this event for the next time you may be needed an imaging study with use of contrast. Pls get a drug allergy test done, once fit from this condition for future safety.