Effect of administered activity on precision in the assessment of renal function using gamma camera renography

Split and total renal function are commonly assessed from time-activity curves obtained from gamma camera renography with 99Tcm-diethylenetriamine pentaacetate (99Tcm-DTPA) and 99Tcm-mercaptoacetyl-triglycine (99Tcm-MAG3). The impact of the statistical noise associated with these curves on the total precision in split and total renal function impairment was studied at different levels of administered activity by simulation. The simulation consisted of generated time-activity curves, with statistical noise corresponding to the administration of 10-400 MBq 99Tcm-DTPA or 7.5-150 MBq 99Tcm-MAG3. Our results indicate that the error induced by statistical noise in split renal function calculations is generally very low (< 3% at 100 MBq 99Tcm-DTPA or 75 MBq 99Tcm-MAG3) and only affects precision slightly in calculations at 45-50 MBq 99Tcm or more. Similar results were obtained for precision in GFR calculations, where the total error increased from 12.3% at 100 MBq 99Tcm-DTPA to 12.8% at 50 MBq, but decreased to 12.0% at 400 MBq. Consequently, statistical noise has a minor effect on the precision in split and total renal function calculations at commonly used activity levels when it is reduced to approximately 50 MBq.