Development of a defect model for renal pediatric SPECT imaging research

Children generally are at greater risk from radiation exposure due to their greater sensitivity to radiation and the longer time frame after exposure during which effects can manifest themselves. Thus, reducing radiation exposure is a major concern in pediatric nuclear medicine imaging. Lower administered activities (AA) can reduce patient radiation exposure, but also result in reduced diagnostic accuracy. Typically, the administered activity for diagnostic nuclear medicine imaging of children is based on patient weight, but our previous studies have shown that weight alone may not be sufficient to accurately determine an optimal patient-specific AA. The ultimate goal of this work is to investigate the tradeoff between image quality and radiation risk as a function of AA, patient age, gender and body habitus that can be used to guide dosing of dimercaptosuccinic acid (DMSA) SPECT, a common pediatric nuclear medicine procedure for assessing renal function. In this work we created a model of kidney function defects and used it to generate defects for a population of anthropomorphic reference phantoms with realistic age-dependent variations in anatomy and pharmacokinetic model based organ uptakes. The population includes 90 phantoms modeling both genders, variations in height and weight, and ages from newborn to 15 years. The defects generated were projected using an analytic projection code that models physical image degrading effects and were scaled with variations in organ uptake based on a new kinetic model fit to published data and parameters extracted from pediatric SPECT images. Combined with a previously-generated database of projections, the defect database will be used in image quality studies to determine the relationship between image quality, administered activity, and patient height and weight. In conjunction with already-calculated risk estimates, these will provide data to inform guidelines for pediatric dosing of DMSA.