Brain single-photon emission computed tomography for behavior disorders in children

Abstract

Single-photon emission computed tomography (SPECT) of the brain has been used to define functional abnormalities in two groups of childhood behavior disorders: (1) a "primary" category in which there is exclusive or predominant presentation with cognitive and/or behavioral dysfunction and (2) encephalopathies, often defined etiologically at the biochemical or molecular level, in which clinical expression includes, but is not confined to, neural dysfunction. Radiopharmaceuticals available for such studies are manifold, but those used to date have been predominantly perfusion agents, eg, Xenon-133 (133Xe) and technetium-99m (99mTc) hexamethylpropylene amine oxime, and studies with [99mTc]bicisate are eagerly awaited. Xenon-133 studies require that the patient be in the field of view of the detector while the tracer is administered. This renders it difficult for a subject to perform cognitive and other exercises while being imaged, because the environment is quite foreign. On the other hand, the 99mTc-labeled perfusion agents permit a scintigraphic "snapshot" of regional cerebral blood flow during a behavioral event without having to have the patient under the imaging instrument. Thus, one can separate the administration of the radiotracer, which can be done under more controlled and physiological conditions, from the actual imaging. In addition, greater spatial resolution is achieved with the technetium-based agents. Currently, multidetector or dedicated annular crystal-type cameras are the preferred brain SPECT devices, and they are essential to applications such as cortical "activation mapping" or tomographic detection of receptor systems. Close attention to technical detail and standardization of the child's behavioral environment during the investigation are critical to a successful study. The relative advantages and disadvantages of qualitative versus semiquantitative analysis of imaging date are reviewed. Among primary behavioral disorders, 133Xe SPECT studies in attention deficit disorder-hyperactivity (ADHD) have suggested a pattern of hypoperfusion of striatal and periventricular structures with sensorimotor cortical hyperperfusion. This pattern is consistent with some neurophysiological models of the disorder. In cerebral palsy, perfusional abnormalities have paralleled clinical deficits and may offer information to help predict outcome. The important field of childhood affective disorders (schizophrenia, juvenile autism, depression, etc) remains largely unstudied with SPECT. Finally, representative examples of the use of SPECT to study perfusion in encephalopathies with behavioral expression (phenylketonuria, MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes) syndrome, Wilson's disease, etc) are given.