Excretory tracers that are rapidly filtered and excreted into urine (eg, iodine-125 iothalmate, 99 m Tc diethylenetriamine pentaacetic acid [DTPA], 99 m Tc mercaptoacetyltriglycine-3 [MAG3]) are used to assess glomerular filtration rate (GFR) and overall renal perfusion.