Renal clearance and extraction parameters of ortho-iodohippurate (I-123) compared with OIH(I-131) and PAH

o-[¹³¹I]iodohippurate [OIH-(I-131)] has been used for many years in the estimation of effective renal plasma flow. This compound suffers from low photon yield and poor images when the quantity used is limited to stay within a reasonable radiation dose. To test the validity of substituting I-123 for I-131, a series of experiments was performed in a surgically prepared dog model. The extraction ratios and clearance values OIH(I-123) prepared from radionuclidically pure I-123 were compared with those of commercial OIH(I-131) and PAH. The extraction ratios for OIH(I-123) and OIH(I-131) were 0.65 and 0.67, representing 0.86 and 0.88 that of PAH, respectively. The clearance values (cc/min/kg) for the I-123 and I-131 compounds were almost identical (P = 0.77). Therefore OIH(I-123) can be used to estimate effective renal plasma flow; moreover, because of the high yield within an acceptable radiation dose range, images of good quality can be produced.