Impact of injection time on migration of SPECT seizure onset in temporal lobe epilepsy

Abstract

In this work, we investigated an impact of injection time on migration of seizure-onset in ictal/interictal single photon emission computed tomography (SPECT) study for patients with temporal lobe epilepsy. We selected 33 patients with refractory temporal lobe epilepsy who underwent ictal/interictal SPECT studies and had preoperative intracranial EEG result or surgical resection which was used as reference for seizure location. We divided all patients into two groups, which are the fast and the delayed groups; the delayed group comprised patients with injection time more than a cutoff time and vice versa. Using the subtraction ictal-interictal SPECT co-registered with SPECT (SISCOS) with varied Z-threshold (1.0, 1.5, 2.0 and 2.5), a method similar to subtraction ictal SPECT co-registered to magnetic resonance imaging (MRI) (SISCOM), a seizure-onset region in the SISCOS image was localized at the region with maximum sum of Z-scores. For each pair of cutoff time and Z-threshold, we determined the migratory proportion which was defined as the proportion of patients whose seizure-onset location based on SISCOS image was discordant with the reference. At cutoff time of 32-35 seconds and the Z-threshold of 2.0, the migratory proportion values were 7/26 (26.9%) and 5/7 (71.4%) in the fast and the delayed groups, respectively. At the same range of cutoff time with the Z-threshold of 2.5, the migratory proportion was 8/26 (30.8%) in the fast group while the proportion was 5/7 (71.4%) in the delayed group. Using Fisher's exact test, the migratory proportion values at the Z-threshold of 2.0 and 2.5 were significantly different between the fast and the delayed groups (p = 0.0709 and 0.0838, respectively), suggesting that patients with temporal lobe epilepsy who undergo an ictal/interictal SPECT study with injection time longer than 35 seconds tend to have seizure-onset zone migration in the SISCOS analysis with the traditionally-used Z-threshold of 2.0.

PET and ictal SPECT can be helpful for localizing epileptic foci

“…Concordance of SISCOM, SOZ and resected area was correlated with 6-month postoperative seizure freedom. The authors conclude that injection delay should be shorter then 25 s. A more systematical approach to injection time and SISCOM threshold to avoid detection related to seizure propagation showed a recommendation of injection latency below 35 s [ 50 ].…”

Application value of molecular imaging technology in epilepsy

“…A study suggested that the correct location of epileptic foci is related to the injection time of the tracer. If the injection time surpasses 35 seconds, epileptic foci will migrate, and the detection accuracy will decrease (Ramchuankiat S, et al, 2017). If the time can be controlled to within 15 seconds after seizures, the accuracy will be improved (Theodore WH, 2017).…”

Evidence based noninvasive presurgical evaluation for patients with drug resistant epilepsies

“…A previous review on this topic in this journal [69] emphasized that by the time the tracer reaches the brain, around 10-60 s after the injection added to the "time-lost" before starting and during the injection, the seizure activity may have dissipated or propagated resulting in iSPECT study showing the propagation pattern instead of onset, especially in seizures with a rapid spread like in ETLE. A more systematic approach to injection time and SISCOM threshold to avoid detection related to seizure propagation showed a recommendation of injection latency below 35 s [71]. STATISCOM showed overall higher agreement rates than SISCOM with localization of the epileptogenic zone.…”