IODOHIPPURIC ACID I-131 (ortho-Iodohippuric Acid I-131, [I-123]-OIH) is an iodine-containing compound used in pyelography as a radiopaque medium. Iodine-123 labelled ortho-Iodohippuric acid was used in the early 1970's as a kidney imaging agent or tracer that "lights-up" inside your body when scanned, but over the years its use has declined. [I-123]-OIH is primarily extracted by the renal tubules and has excellent pharmacokinetic properties, with a clearance only slightly less than that of p-aminohippuran, but its use has been compromised by the suboptimal imaging characteristics of the 364-keV photon of 131I and the delivery of relatively high radiation doses to kidneys and thyroid in patients with impaired renal function