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

Abstract

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.

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

“…We and others have previously looked at the perfusion changes of short versus long seizures and noted that a return to baseline levels can occur more quickly for very short seizures (25). Likewise, for times later than 100 seconds after seizure onset, perfusion decreases of approximately 50% are noted and can persist for many minutes (26).…”

Quantitative multi-compartmental SPECT image analysis for lateralization of temporal lobe epilepsy

“…Injection latency relative to electrographic or clinical ictal onset must be minimized to restrict the volume of hyperperfusion to the immediate ictogenic zone and, at the same time, limit the network effect elicited by propagation of electrochemical activity (Cross et al, 1995; Lee et al, 2006; Zubal et al, 1999). An injection delay of under 20 seconds after ictal onset provides SPECT imaging that correlates significantly with correct localization in neocortical epilepsy (Lee et al, 2006).…”

Ictal brain SPET during seizures pharmacologically provoked with pentylenetetrazol: a new diagnostic procedure in drug-resistant epileptic patients

“…These include semi-quantitative analysis based on calculation of the ratios between regions of interest and reference regions [26], quantitative analysis involving calculation of the greatest increase or decrease after co-registration, normalisation and subtraction of interictal-ictal images [31,33], co-registration with anatomical neuro-images [31,35] and use of statistical parametric mapping software programs [36]. Although both traditional and more sophisticated techniques of quantification have (despite their various limitations) undoubtedly enhanced the diagnostic accuracy of SPET by objectively supporting visual analysis, none of these methods can overcome a basic limitation, namely the timing of ictal injection, which is a common denominator [31,32,37,38]. Truly ictal SPET studies are logistically difficult to obtain.…”