Clinical use of ictal SPECT in secondarily generalized tonic-clonic seizures.

Partial seizures produce increased cerebral blood flow in the region of seizure onset. These regional cerebral blood flow increases can be detected by single photon emission computed tomography (ictal SPECT), providing a useful clinical tool for seizure localization. However, when partial seizures secondarily generalize, there are often questions of interpretation since propagation of seizures could produce ambiguous results. Ictal SPECT from secondarily generalized seizures has not been thoroughly investigated. We analysed ictal SPECT from 59 secondarily generalized tonic-clonic seizures obtained during epilepsy surgery evaluation in 53 patients. Ictal versus baseline interictal SPECT difference analysis was performed using ISAS (http://spect.yale.edu). SPECT injection times were classified based on video/EEG review as either pre-generalization, during generalization or in the immediate post-ictal period. We found that in the pre-generalization and generalization phases, ictal SPECT showed significantly more regions of cerebral blood flow increases than in partial seizures without secondary generalization. This made identification of a single unambiguous region of seizure onset impossible 50% of the time with ictal SPECT in secondarily generalized seizures. However, cerebral blood flow increases on ictal SPECT correctly identified the hemisphere (left versus right) of seizure onset in 84% of cases. In addition, when a single unambiguous region of cerebral blood flow increase was seen on ictal SPECT, this was the correct localization 80% of the time. In agreement with findings from partial seizures without secondary generalization, cerebral blood flow increases in the post-ictal period and cerebral blood flow decreases during or following seizures were not useful for localizing seizure onset. Interestingly, however, cerebral blood flow hypoperfusion during the generalization phase (but not pre-generalization) was greater on the side opposite to seizure onset in 90% of patients. These findings suggest that, with appropriate cautious interpretation, ictal SPECT in secondarily generalized seizures can help localize the region of seizure onset.

Ratio-images calculated from interictal positron emission tomography and single-photon emission computed tomography for quantification of the uncoupling of brain metabolism and perfusion in epilepsy.

PURPOSE: Image processing techniques were applied to interictal positron emission tomography (PET) and single-photon emission computed tomography (SPECT) brain images to aid in the localization of epileptogenic foci by calculating a functional image that represents the degree of coupling between perfusion and metabolism. Uncoupling of these two functions has been demonstrated to be a characteristic of epileptogenic tissue in temporal lobe epilepsy and has the potential to serve as a diagnostic measure for localization in other areas as well. METHODS: Interictal PET ((18)F-FDG) and interictal SPECT ((99m)Tc-HMPAO) scans were acquired from 11 epilepsy patients. The metabolism and perfusion images were three-dimensionally spatially registered, and a functional ratio-image was computed. These functional maps are overlaid onto a three-dimensional rendering of the same patient's magnetic resonance imaging anatomy. RESULTS: In all patients, an average uniform perfusion-to-metabolism ratio showed approximately constant values throughout most of the whole brain. However, the epileptogenic area (confirmed on surgery) demonstrated an area of elevated perfusion/metabolism in the grey matter. CONCLUSIONS: Although hypometabolism in the PET image was observed in most of these patients, the calculation of a functional ratio-image demonstrated localized foci that in some cases could not be observed on the PET image alone. The ratio-image also yields a quantitative measure of the uncoupling phenomenon.

Influence of technetium-99m-hexamethylpropylene amine oxime injection time on single-photon emission tomography perfusion changes in epilepsy.

By digitally computing perfusion changes from ictal or postictal (peri-ictal) injections referenced to those acquired interictally, an enhanced method for localizing the epileptogenic area is reported. Computer-based image processing methods for quantifying regional percent change in the brain are applied to a group of 19 epilepsy patients after the injection of technetium-99m hexamethylpropylene amine oxime (HMPAO) and after acquiring single-photon emission tomography (SPET) data. Each patient's region of epileptogenesis was independently localized through pathology and/or successful surgery. The positive and negative quantitative perfusion changes were plotted as a function of the time of the 99mTc-HMPAO ictal injection. This time scale was normalized relative to the seizure duration and is referenced to the time of seizure termination. Eight patients, injected ictally, demonstrated perfusion increases of 25%-100% in the area of known epileptogenesis. Five patients, injected immediately after seizure cessation, demonstrated excessive perfusion decreases of 30%-92% associated with the region of seizure onset. Six patients, injected well after seizure termination, demonstrated hypoperfusion changes less than 30% at the epileptogenic area. Observations on perfusion changes calculated from 99mTc-HMPAO SPET scans, as a function of normalized time, support a progression from ictal hyper- to excessive hypo-, then finally to persistent interictal hypoperfusion. By applying this perfusion pattern model and by noting the time of injection for peri-ictal images, an improved method for localizing the epileptogenic area is demonstrated.