 The dose of radioiodine 123I is typically tolerated by individuals who cannot tolerate contrast mediums containing larger concentration of stable iodine such as used in CT scan, intravenous pyelogram (IVP) and similar imaging diagnostic procedures.Iodine is not an allergen.123I is also used as a label in other imaging radiopharmaceuticals e.g.metaiodobenzylguanidine (MIBG) and ioflupane.