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paralleled hypometabolism. It is not clear, however, whether the reduction was due to reduced
perfusion, loss of tissue or reduction of receptor binding171 and further work is needed to
clarify this.

Serotoninergic neurones

Alpha-[11C]methyl-L-tryptophan ([11C]AMT) is a marker for serotonin synthesis. In
children with tuberous sclerosis, uptake was increased in some tubers that appeared to be the
sites of seizure onset. Other tubers showed decreased uptake. In contrast, FDG-PET showed
hypometabolism in all tubers. This study suggests that [11C]AMT PET may be useful to
detect epileptogenic foci, in patients with tuberous sclerosis, and possibly other forms of
cerebral malformation172,173. In 39% of patients with MCD or cryptogenic focal epilepsies
there was focal increased uptake of alpha-MT in the epileptogenic area. This may be a further
useful tool for localising epileptic foci174. Increased AMT uptake has been reported to be
more specific, but less sensitive for identifying the epileptic focus in children with refractory
epilepsy175, and to be increased in the hippocampus ipsilateral to the focus in TLE176.

In summary, studies with PET are useful for investigating the neurochemical abnormalities
associated with the epilepsies, both static inter-ictal derangements and dynamic changes in
ligand-receptor interaction that may occur at the time of seizures. The development of further
ligands in the coming years, particularly tracers for excitatory amino acid receptors, subtypes
of the opioid receptors and the GABAB receptor, are necessary to further understand the
processes that give rise to and respond to the various forms of the epilepsies. All functional
data needs to be interpreted in the light of the structure of the brain. Coregistration with high
quality MRI is essential. It will also be important to carry out parallel studies with in vitro
autoradiography and quantitative neuropathological studies on surgical specimens and post-
mortem material.

Conclusion

There have been significant advances in brain imaging that have revolutionised epilepsy
management and particularly surgery. Structural MRI continues to improve and
contemporary optimal scans may reveal lesions that were previously not evident. In
consequence, rescanning individuals with previously unremarkable MRI is appropriate.

If structural MRI does not indicate a plausible structural cause of the epilepsy, or if a
demonstrated lesion is discordant with clinical and EEG data, functional imaging with 18F-
fluorodeoxyglucose PET, and SPECT of ictalinter-ictal cerebral blood flow can infer the
area that contains the epileptic focus and guide intracranial electrode placements. PET with
specific ligands is scientifically attractive, but has not had a major impact on epilepsy surgery
practice due to limited availability. A recent study assessed the relative predictive value of
FDG PET, ictal SPECT and magnetoencephalography against the gold standards of
intracranial EEG and outcome of epilepsy surgery. Magnetoencephalography had a high
correlation with intracranial EEG, and both PET and ictal SPECT were of additional
localising value177. All three modalities were of benefit in predicting seizure-freedom
following surgery178.

Simultaneous EEG and fMRI can visualise the location of inter-ictal epileptic discharges.
These data can assist in deciding on the placement of intracranial electrodes to define the site
of seizure onset.

Functional MRI to lateralise language and localise primary motor and somatosensory cortex
has entered clinical practice and contributed to the decline of the carotid amytal test. If