Quantitation of renal 99mTc-DMSA uptake in maturing children: Implications for dosing guidelines in pediatric imaging

Objectives As part of an ongoing dose-reduction effort in pediatric imaging we are developing pharmacokinetic (PK) models for the most frequently used pediatric imaging agents, based on measurements in children. The PK models can be used as input to other studies to achieve standardized dosing, provided that adequate diagnostic image quality is obtained consistently with the dose-reduction objective of the Image Gently campaign. Currently available pediatric PK data are severely limited, and this makes the study of the kinetics of these agents in children very challenging. In this study we have measured the kidney uptake of 99mTc-DMSA, the renal imaging agent, in a wide age-range of pediatric patients from Boston’s Children Hospital (BCH).

Methods To establish a PK model for 99mTc-DMSA applicable to pediatric patients of different ages, we retrospectively evaluated the renal uptake of this agent in 36 children (ranging in age from 1 to 16 years old) from BCH. The percent injected activity (% IA) present in the kidneys at time of diagnostic image acquisition (3 to 4 h after injection) was estimated from SPECT/CT images using quantitative reconstruction that accounted for attenuation, scatter and collimator response. Kidney concentration at the imaging time was compared with model prediction. Previously published patient data for 99mTc-DMSA uptake in the liver, spleen and whole body, were also used as input to the PK model. SAAM II compartmental modeling and analysis software was used for PK model development.

Results The mean percent injected activity in the kidneys at 3.0 ± 0.6 h post injection was 33 ± 6 % (range: 12 to 43 %). The percent injected activity (% IA) in the kidneys was independent of age and weight. Our preliminary PK model for 99mTc-DMSA successfully fits the renal imaging data from BCH and the pediatric clinical data on liver, spleen and whole-body found in literature reports.

Conclusions Measurements of renal uptake of 99mTc-DMSA in a wide age-range of pediatric patients from BCH provided an indispensable data set for the PK model development. Further validation of the PK model depends on the availability of longitudinal imaging data in pediatric patients for this agent. We are working with BCH on a protocol to collect such data.