Application of PET/CT in children

Abstract

Positron Emission Tomography (PET) can dynamically image trace amounts of radiopharmaceuticals in vivo. By applying appropriate tracer kinetic models, tracer concentrations can be determined quantitatively. In addition to superior spatial resolution and quantitative potential, PET also offers much greater sensitivity (i.e., number of y-rays detected per unit injected dose) than single photon emission computed tomography (SPECT). Furthermore, the biologic ubiquity of the elements that are positron emitters gives PET unprecedented power to image the distribution and kinetics of natural and analog biologic tracers. Because of the exquisite sensitivity of detection systems to y-ray emission, these biologic probes can be introduced in trace amounts (nanoor even picomolar concentrations) that do not disturb the biologic process under investigation. By combining a tracer that is selective for a specific biochemical pathway, an accurate tracer kinetic model, and a dynamic sequence of quantitative images from the PET scanner, it is possible to estimate the absolute rates of biologic processes in that pathway. Examples of such processes that have been successfully measured with PET include regional cerebral and myocardial blood flow, rates of glucose utilization, rates of protein synthesis, cerebral and myocardial oxygen consumption, synthesis of neurotransmitters, enzyme assays, and receptor assays. In summary, some of the distinctive advantages of PET are its exquisite sensitivity, the flexible chemistry, and the better imaging characteristics of PET isotopes. Thus PET provides access to biological processes that is well beyond the scope of current MR technology. The radioactive decay of many radioisotopes generates penetrating photons capable of escaping outside the matter in which the isotopes are located. From this radiation it is possible to image the spatial distribution of such isotopes inside an object. When imaging humans, it is necessary to use photons capable of escaping undeflected from a few