Wikipedia
Ortho-iodohippurate is an analogue p-aminohippuric acid for the determination of effective renal plasma flow. Labelled OIH has a significantly higher clearance than other radiopharmaceutical yet developed and is eminently suitable for renography. It is eliminated mainly by tubular secretion. In patients with normally functioning kidneys, 85% of the OIH may be found in the urine 30 minutes after intravenous injection.
OIH was first labelled with I by Tubis and colleagues (Tubis, Posnick and Nordyke in 1960) and for many years this was the only radiopharmaceutical for renography. I has a half-life of 8 days and emits high-energy gamma rays (364 KeV) in addition to beta particles. These physical characteristics were acceptable for probe studies when quantities of the order 1-2 MBq (25-50 μCi) were administered, but they are far from ideal for gamma camera studies which demand a higher activity and a gamma ray emission of lower energy. The introduction of OIH labelled with I, with its short physical half-life (13 hours) and its gamma emission of 159 KeV has greatly improved the diagnostic potential of renal studies by combining the production of high-quality functional images with the ability to derive a renogram. The only factor limiting its widespread use is restricted availability and the expense involved in its cyclotron production.