Pediatric Movement Disorders - Diagnostic Methods

Functional Imaging

Functional MRI (fMRI) is a research technique that seeks to look at how the brain functions, rather than its structure. In particular, the response of different brain areas may be measured while the brain is working. An area of the brain that is active uses more blood, and this blood flow is measured with fMRI. While in the scanner, the child must be awake and able to cooperate with detailed instructions. This technique is currently used primarily for research; it is likely that it will become an important method for investigating injury to the brain as well as the capacity for the brain to recover function by shifting activity to uninjured areas.

Positron Emission Tomography (PET) scanning uses special chemicals that are injected into the child. These chemicals are attached to tiny amounts of a radioactive tracer. The PET scanner then detects when the radioactivity breaks down and it reconstructs an image. The amount of radioactivity is so low that it causes no injury to the child; however, it is measurable by very sensitive detectors in the scanner. A form of glucose (i.e., fluorodeoxyglucose or FDG) is most commonly used as the chemical tracer. Highly active areas of the brain use more glucose and, therefore, become visible on the scan. Injured areas of the brain may use less glucose. Many other tracers are possible for research purposes, and in movement disorders, it is often helpful to use fluoro-DOPA as a tracer. This tracer is used to investigate basal ganglia function. Other newer tracers look at dopamine synthesis, binding, and reuptake in the striatum of the basal ganglia. This may be extremely helpful in diagnosing Parkinson's disease, dopa-responsive dystonia (DRD), striatal degeneration, and other disorders. The disadvantage of PET scanning is that most hospitals do not have access to the equipment.

Single Photon Emission Computed Tomography (SPECT) is similar to PET scanning but uses a different type of radioactive tracer. A gamma-camera collects gamma rays emitted by the tracer and then a computer reconstructs a two-dimensional or three-dimensional image. The resolution is not as good as PET; however, the tracers are easier to synthesize and most hospitals have SPECT equipment. Unfortunately, tracers useful for studying basal ganglia function are not yet readily available for SPECT. As with PET, there are no known complications, other than a possible allergic reaction to the tracer, which is very rare.