Subtraction ictal SPECT coregistered to MRI for seizure focus localizationin partial epilepsy

Peri-ictal single-photon emission computed tomography (SPECT) of the brain is increasingly used in localizing the seizure focus in presurgical evaluat ion of patients with partial epilepsy. However, traditional side-by-side vi sual interpretation of ictal and interictal SPECT films is hampered by diff erences in slice location and tracer activity, Precise correlation of the s eizure focus with a high-quality image of the underlying brain anatomy can improve the physician's understanding of seizure neurophysiology and assist in surgical planning. Computer-based methods have been developed for align ing, normalizing, and subtracting digital ictal and interictal SPECT images of the patient's brain to produce a map of the blood flow changes occurrin g between the seizure and resting states. These maps are then aligned with a high-resolution magnetic resonance image (MRI) of the patient's brain ana tomy and fused to identify anatomical regions involved in the seizure. The purpose of this article is to review the technical components and clinical implementation of subtraction ictal SPECT, as well as to discuss recent tec hnological advances that could extend and improve the diagnostic and locali zing capacity of this method.