Abstract
BackgroundIn epilepsy patients, SISCOM or subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging has become a routinely used, non-invasive technique to localize the ictal onset zone (IOZ). Thresholding of clusters with a predefined number of standard deviations from normality (z-score) is generally accepted to localize the IOZ. In this study, we aimed to assess the robustness of this parameter in a group of patients with well-characterized drug-resistant epilepsy in whom the exact location of the IOZ was known after successful epilepsy surgery. Eighty patients underwent preoperative SISCOM and were seizure free in a postoperative period of minimum 1 year. SISCOMs with z-threshold 2 and 1.5 were analyzed by two experienced readers separately, blinded from the clinical ground truth data. Their reported location of the IOZ was compared with the operative resection zone. Furthermore, confidence scores of the SISCOM IOZ were compared for the two thresholds.ResultsVisual reporting with a z-score threshold of 1.5 and 2 showed no statistically significant difference in localizing correspondence with the ground truth (70 vs. 72% respectively, p = 0.17). Interrater agreement was moderate (κ = 0.65) at the threshold of 1.5, but high (κ = 0.84) at a threshold of 2, where also reviewers were significantly more confident (p < 0.01).ConclusionsSISCOM is a clinically useful, routinely used modality in the preoperative work-up in many epilepsy surgery centers. We found no significant differences in localizing value of the IOZ using a threshold of 1.5 or 2, but interrater agreement and reader confidence were higher using a z-score threshold of 2.
Highlights
In epilepsy patients, SISCOM or subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging has become a routinely used, non-invasive technique to localize the ictal onset zone (IOZ)
It has been reported that the correct detection of the IOZ improves by the use of SISCOM versus the conventional sideby-side comparison of ictal and interictal single photon emission computed tomography (SPECT) images (83 vs. 31%) [4]
Patients were included in this study if they (1) had undergone both ictal and interictal SPECT-imaging before surgery, (2) had a volumetric preoperative magnetic resonance imaging (MRI), and (3) were completely seizure free in the postoperative period for at least 1 year after surgery or had less than three seizures in the postoperative period after which they were seizure free for at least 1 year [17]
Summary
SISCOM or subtraction ictal single photon emission computed tomography co-registered to magnetic resonance imaging has become a routinely used, non-invasive technique to localize the ictal onset zone (IOZ). SISCOMs with z-threshold 2 and 1.5 were analyzed by two experienced readers separately, blinded from the clinical ground truth data Their reported location of the IOZ was compared with the operative resection zone. A selected group of patients with medically refractory epilepsy, making up to one third of all epilepsy patients, can benefit from epilepsy surgery with a chance of seizure remission in about 60% after temporal lobe resection and about 50% after extratemporal lobe resection [1]. In this subgroup, it is of highest importance to exactly locate the ictal onset zone (IOZ). SISCOM is a highly valuable non-invasive method in the preoperative workup of these patients if it can be acquired and analyzed properly
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