Deadtime correction in measurement of fractional renal accumulation of Tc-99(m)-MAG3

Fractional renal accumulation of a radiotracer is often used to measure ren al function with camera-based methods. We evaluated the effect of deadtime count loss on the calculation of fractional renal accumulation of Tc-99(m)- mercaptoacetyltriglycine (Tc-99(m)-MAG3). In 15 patients, dynamic renal sci ntigraphy was performed after the injection of 250 MBq of Tc-99(m)-MAG3. A reference source was placed on the periphery of the field of view of the ga mma camera to monitor the loss of counts in dynamic imaging. The activity i n the syringe was also counted with the camera to measure the injected dose , and the deadtime count loss in the syringe was computed from the observed count rate and deadtime in imaging a point source. Fractional renal accumu lation, the ratio of renal accumulation on dynamic imaging to the injected dose, was assessed with and without correction for deadtime loss. Fractiona l renal accumulation was overestimated by 4.1% with no deadtime correction, when the value after correction for loss in both syringe counts and dynami c imaging was used as a standard. It was underestimated by 4.0% with correc tion for syringe counts only The results suggest that correction for count loss only in measuring the injected dose does not lead to a significant imp rovement in the accuracy of estimating renal function with camera-based met hods. ((C) 1999 Lippincott Williams & Wilkins).