SPECT shows the blood flow in the brain. A safe, very low-level radioactive compound is injected into the patient’s arm, and the particles it emits are measured. The more blood that flows through a certain area, the more particles are emitted. The result is displayed as a picture with different colors representing different levels of blood flow.
This test is readily available in most hospitals, but it is seldom needed routinely in epilepsy. SPECT scans obtained during or immediately after a seizure may show increased blood flow in the area where seizures arise. Scans performed between seizures can be misleading, however.
New computer techniques allow doctors to measure the differences between SPECT scans taken during ("ictal") and those taken between ("interictal") seizures to obtain "subtraction" SPECT images. These can be superimposed onto the patient’s MRI in an effort to pinpoint the seizure focus. This technique may be most helpful when seizures begin outside the temporal lobe and MRI scans do not show a structural abnormality.
Your doctor may want you to undergo "ictal" SPECT – or a SPECT scan obtained during a seizure. The test isn’t actually performed during the seizure, but the goal is to have the tracer injected during a patient’s seizure. Therefore, this study usually occurs during the video EEG monitoring stay. Usually, the tracer can be used during a certain period of the day (most often between 9 am and 3 pm). The nurse is often instructed to hold all seizure medications to increase the likelihood that a patient will have a seizure. The patient will be very closely monitored during that period for any early signs of a seizure; as soon as the seizure occurs, the nurse will inject the tracer into the IV in the patient’s arm. The patient will then typically be given the morning dose of medications and will be sent to the radiology department for the scan. The SPECT machine is neither loud nor confining like the MRI machine and imaging is painless to the patient.