Ictal SPECT in epilepsy: the advantages of automatic dose injection system

Abstract

Epilepsy is the most prevalent chronic neurological disorder in the field of neurology. It is estimated to affect five out of every 1000 people in the population. The range of drug treatments currently available provides adequate control of the disorder for 75% of patients. However, this leaves 25% of sufferers for whom even the use of polytherapy at maximum dosage is not effective [1]. It is in this latter group that surgery is considered an option to limit the frequency of seizures. Resective epilepsy surgery is based on the premise that if the epileptogenic area is completely removed, the patient will be seizure-free. Presurgical evaluation of patients with drugresistant epilepsy can identify the epileptogenic area or region and a successful surgical outcome will depend on accurate preoperative localization of the seizure focus. Video-EEG monitoring, with scalp and sphenoidal electrodes, is the method of choice for localizing seizure focus. However, scalp EEG is often inadequate, especially for deep lesions or in rapidly spreading seizures, where it either fails to register or identifies activity as propagation rather than seizure onset [2]. In order to avoid invasive recordings with intracraneal electrodes, structural and functional imaging procedures have been developed to supplement EEG findings. MRI, PET and ictal and interictal SPECT are the most frequently used procedures for localizing seizure focus. Brain SPECT is a nuclear medicine exploration that can map the distribution of cerebral blood flow at the moment of tracer injection. If a radioactive tracer injection can be given during the epileptic seizure, a brain SPECT will localize the onset zone by showing increased uptake [3]. Ictal SPECT is probably the best imaging procedure to localize the seizure onset zone before surgery in patients with complex partial seizures [4]. A good ictal SPECT is not always easy to obtain, however, because a seizure is a dynamic process in which several brain regions can become involved sequentially [5,6]. As a consequence, ictal SPECT as a technique has been limited to a few specialist epilepsy centers. Its complex methodology means that it is not routinely available in clinical practice in the majority of nuclear medicine departments. The biggest problem with ictal SPECT is that the radiotracer dose has to be calculated and administered manually, a time-consuming process that requires the constant availability of trained medical staff at the bedside for extended periods. As seizure onset is unpredictable, we must maintain a tracer-filled syringe close to the patient’s bed, waiting for a seizure to occur. The urgency of calculating the correct radioactive dose and rapidly administering it to a patient in the middle of an epileptic attack is stressful, complicated and can increase the risk of radioactive contamination. As any delay between seizure onset and tracer injection can seriously compromise results (giving false readings caused by activity spread), it is essential that the injection procedure takes as little time as possible.