1 If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test. 2  Have a health condition, such as diabetes, sickle cell anemia, or kidney problems. 3  You may need to change your medicine schedule. Have any metal implanted in your body. 2  This helps your doctor know if the test is safe for you. 3  Tell your doctor if you have: 4  Heart and blood vessel devices such as a coronary artery stent, a pacemaker, an ICD (implantable cardioverter-defibrillator), or a metal heart valve.