Absolute 99Tcm-DMSA renal uptake in children: optimum time to scan

Absolute renal uptake was measured at 2, 4 and 6 h in 27 patients in order to determine a more convenient time for uptake compared with the 6-h measurement proposed by other authors. Measurements made at 2 and 4 h would need to be increased by 20 and 6%, respectively, to convert to the value at 6 h. Measurements at 4 h are a reasonable compromise to achieve a high-count/low-background image in a reasonable time and to obtain a good estimate of the predicted 6 h uptake at a single scanning session. The percent renal uptake at 6 h, U(6), can be derived from the percent uptake measured at t hours after injection, U(t), using the following formula: U(6) = U(t) x CF(t), where CF(t) = 1.0 + 0.03 (6 - t) for 4 < or = t < or = 6.