Administered activity of Tc-99(m)-MAG3 for gamma camera renography in children

A method of calculating the activity of Tc-99(m)-MAG3 to be administered to children of different ages has been developed and evaluated. The suggested administered activity schedule is only valid for estimation of split renal function. The activity required to obtain the same count rate over the kid neys for all ages was calculated as a fraction of the activity administered to an adult by using a biokinetic model and taking attenuation effects int o account. The activity schedule is based on the age of the child and was t ested using renograms from patients of different ages. Statistical noise wa s added to the smoothed renograms simulating an injected activity correspon ding to 45 MBq for an adult. The precision in the determination of split re nal function calculated with four different methods was determined for 500 simulated renograms. The precision was approximately the same for all ages, but varied with the method used. The activity to be administered to a very small child is 90% of the adult activity, decreases to less than 50% betwe en 2 and 5 years of age, and then slowly increases to 100% as the child gro ws to adulthood. ((C) 1999 Lippincott Williams & Wilkins).