Positron emission tomography (PET) uses harmless radioactive tracers to understand the general location of seizure activity. These tracers are less concentrated in seizure-prone areas than in other regions of the brain.
PET scans usually last between 15 to 90 minutes, and are often performed alongside an EEG. Before undergoing the procedure, children are advised to fast for 4 to 6 hours and avoid caffeine or drugs, which could alter the results. The most commonly used tracer, known as 2-deoxt-2flouro-D-glucose (FDG), gauges the brain’s activity based on its rate of sugar consumption. Accordingly, blood sugar levels are checked before the tracer is injected and patients with high blood sugar must reschedule their scan.
PET is considered the best imaging method to reveal how the brain functions between seizures. These scans could help clinicians understand status epilepticus (one seizure longer than 30 minutes or multiple seizures in a 30-minute period).
Because the scans provide such generalized information, their uses are somewhat limited. They can guide subdural electrodes into place, for example, but they cannot map the precise boundaries for brain surgery. However, PET can help predict the outcomes of epilepsy surgery, particularly when MRI and EEG results are not conclusive. Scans that show large affected areas on both sides of the brain may foretell frequent seizures after surgery.
Special uses for PET include:
- Temporal lobe epilepsy: C-flumazenil (FMZ) PET can detect temporal lobe epilepsy with high sensitivity, uncovering evidence of disease in 85 percent of people with normal MRI results. FMZ-PET can detect seizure onset more sensitively and accurately than FDG-PET in patients with temporal and extratemporal lobe epilepsy.
- Extratemporal lobe epilepsy: FDG PET can be useful in the presurgical evaluation of extratemporal lobe epilepsy. PET can identify the source of the seizures in frontal lobe epilepsy ranges about 45 to 73 percent of the time, or up to 92 percent of the time if a high-resolution PET scanner is used.
- Infantile spasms: PET is useful in identifying infantile spasms since most children with this type of epilepsy have changes in the brain’s sugar use. Surgery based on a combination of EEG and PET can improve seizure control and lead to a partial or complete reversal of developmental delays.
- Tuberous sclerosis: FDG PET does not effectively distinguish between tubers that cause seizures and those that do not. However, C-alphamethyl-L-tryptophan (AMT) PET is most avidly taken up by seizure-causing tubers and can identify them in two thirds of children.
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