TESTS IN EPILEPSY: OTHER IMAGING TECHNIQUES

Before the development of CT scanning, simple skull X-rays or air-encephalograms (in which the structure of the brain was outlined by injected air) were the only techniques available. These have been superseded entirely. Another technique, angiography, is still used in some patients with epilepsy due to a structural cause. In this technique, an iodine-containing solution which is opaque to X-rays is injected directly into one or other carotid artery (in the neck), or through a catheter introduced into the brachial (elbow) or femoral (groin) arteries and passed into the region of the carotid. Immediately after the injection, a series of X-ray pictures are taken which outlines the arteries and veins containing the iodine solution. This technique identifies precisely any abnormal blood vessels and may be extremely valuable if surgery is being considered on an angioma or tumour. Advances in MRI mean that the circulation can usually be imaged by special pulse techniques and image processing software, so angiography is likely to be superseded in the near future.

Other imaging techniques are available at research centres. These include positron emission tomography (PET), or single photon emission computerized tomography (SPECT). In these procedures, variations in function in different parts of the brain can be imaged.

The technique involves injecting a glucose solution, or breathing oxygen, either of which is labelled with a specially marked atom. The oxygen or glucose is taken up and metabolized by different parts of the brain at different rates. The marker atoms attached to the oxygen or glucose allows images to be obtained which may show an area or areas of the brain which take up a lot of oxygen and glucose during a seizure, and which could be an epileptic focus. Between seizures, the same areas are relatively silent. Such studies may help neurologists and neurosurgeons decide on the suitability of a child or adult for epilepsy surgery.

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