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The practice of nuclear medicine in children is well established for imaging practically all physiologic systems but particularly in the fields of oncology, neurology, urology, and orthopedics. Pediatric nuclear medicine yields images of physiologic and molecular processes that can provide essential diagnostic information to the clinician. However, nuclear medicine involves the administration of radiopharmaceuticals that expose the patient to ionizing radiation and children are thought to be at a higher risk for adverse effects from radiation exposure than adults. Therefore it may be considered prudent to take extra care to optimize the radiation dose associated with pediatric nuclear medicine. This requires a solid understanding of the dosimetry associated with the administration of radiopharmaceuticals in children. Models for estimating the internal radiation dose from radiopharmaceuticals have been developed by the Medical Internal Radiation Dosimetry Committee of the Society of Nuclear Medicine and Molecular Imaging and other groups. But to use these models accurately in children, better pharmacokinetic data for the radiopharmaceuticals and anatomical models specifically for children need to be developed. The use of CT in the context of hybrid imaging has also increased significantly in the past 15 years, and thus CT dosimetry as it applies to children needs to be better understood. The concept of effective dose has been used to compare different practices involving radiation on a dosimetric level, but this approach may not be appropriate when applied to a population of children of different ages as the radiosensitivity weights utilized in the calculation of effective dose are not specific to children and may vary as a function of age on an organ-by-organ bias. As these gaps in knowledge of dosimetry and radiation risk as they apply to children are filled, more accurate models can be developed that allow for better approaches to dose optimization. In turn, this will lead to an overall improvement in the practice of pediatric nuclear medicine by providing excellent diagnostic image quality at the lowest radiation dose possible. [ABSTRACT FROM AUTHOR]