Radiation dose is of special concern in pediatric patients for higher sensitivity in radiation and longer timeframe to manifest stochastic effects. Since body habitus can affect image quality in pediatric patients, it is important to understand the tradeoff between image quality, radiation dose, and body habitus. In this study, B-spline based mathematical phantoms were used to simulate the anatomy of two 10-year old girls having the same weight but different body habitus. Literature data was used to obtain organ uptakes of 99mTc-dimercaptosuccinic acid. Projection data for administered activities (AA) ranging from 0.25 to 1.5 times a standard AA were simulated using an analytic projector modeling attenuation, scatter, and the collimator-detector response followed by simulation of Poisson noise. Kidney function defects were created at several locations in each kidney with varying activity concentration ratios. The projections were reconstructed using filtered-backprojection (FB) followed by 3D Butterworth filter with various cutoff frequencies to find an optimal cut-off frequency. Channelized Hotelling observer and receiver operating characteristics (ROC) methodologies were applied to the reconstructed images for the task of defect detection. Areas under the ROC curve (AUC) were computed to assess the changes in the lesion detection. At higher, non-optimal cutoffs results showed different trade-offs for the lesion detectability between the 2 phantoms indicating that body habitus, and not just weight, is a significant factor in determining image quality for a given AA. However, use of the optimal cutoff resulted in little difference in the image quality versus AA tradeoff for the two phantoms. A population of phantoms spanning the range of pediatric height has been generated and the results of this study will ultimately be extended to the full population in order to provide data needed to establish optimal pediatric dosing guidelines.