SPECT postprocessing for epileptogenic focus localization: SISCOM versus ISAS

Ictal SPECT can be used as an estimate for the epileptogenic zone in people with focal epilepsy. Subtraction of ictal and interictal SPECT scans reveals the area with significant ictal hyperperfusion. Some methods use a control database to also correct for physiological variance. This control database is ideally scanner specific, but it is not trivial to obtain such a database because of ethical issues. In this study, we used a publicly available control database to compare ictal-interictal SPECT analyzed by SPM (ISAS) with the most commonly used subtraction ictal SPECT co-registered to MRI (SISCOM).

Ictal and interictal SPECTs of 26 patients (age range: 7-50 years, 15 adults, 11 children) with focal drug resistant epilepsy in workup for epilepsy surgery were retrospectively analyzed using both SISCOM and ISAS. The control database for ISAS was obtained from the ISAS website. Two groups of blinded reviewers determined the location of ictal hyperperfusion in all datasets. Results were compared between subtraction algorithms and with the resected area (if available) or the suspected epileptogenic zone. The number of significant clusters and the locations of maximum hyperperfusion were compared between algorithms.

The location of ISAS and SISCOM hyperperfusion was the same in 14 patients (54%). ISAS localized in 6 patients where SISCOM did not. Compared to the resected area or suspected epileptogenic zone, SISCOM correctly localized in 55%, while ISAS did in 65% (not significantly different). ISAS shows significantly less clusters than SISCOM. The maximum hyperperfusion was in the reviewer's location in 65% for ISAS and 38% for SISCOM.

ISAS using a publicly available control database gives comparable or better results than SISCOM. ISAS results are easier to interpret than SISCOM results. We show that ISAS is a reliable alternative for SISCOM, which could easily be implemented in epilepsy surgery clinics.

We explored the effectiveness of ISAS as an alternative to the widely used SISCOM for assessing SPECT scans in epilepsy surgery candidates. Utilizing a publicly available control database, we compared the two methods in 26 patients. The results indicate that ISAS might offer increased accuracy and interpretability, making it a promising option, especially for centers without access to a specific control dataset.