BY SARAH OWENS

Arterial spin labeling magnetic resonance imaging (MRI) — a noninvasive imaging technique that measures cerebral perfusion —successfully detected the seizure-onset zone in a majority of patients with drug-resistant focal epilepsy, according to a new study published online on September 29 in Brain.

Changes in blood perfusion in the seizure-generating areas of the brain may be a mechanism by which seizures induce neurological dysfunction, the researchers wrote. By measuring perfusion changes, they said, researchers may be able to localize the seizure onset zone.

Arterial spin labelling (ASL) has the potential to measure these changes, but the technique, they said, has not been widely tested.

The present findings suggest the technique is a "safe, feasible and cost-effective imaging modality that can be used in the postictal period to assist with the localization of the [seizure onset zone]," the study authors, led by Ismael Gaxiola-Valdez, Msc, research associate in the department of clinical neurosciences at the University of Calgary, wrote.

For the study, researchers at the University of Calgary prospectively recruited 21 patients with drug-resistant focal epilepsy who had been admitted to the Seizure Monitoring Unit at the Foothills Medical Centre of the University of Calgary for continuous scalp video electroencephalography monitoring between January 2014 and March 2016. The researchers performed an ASL scan on each of the patients within 90 minutes of a habitual seizure. Then they performed a scan during the patients' interictal period, after they had been free of seizures for at least 24 hours.

They subtracted the patients' postictal data from their interictal ASL data to identify areas of significant postictal hypoperfusion, then compared the location of maximal hypoperfusion to the presumed seizure onset zone to see if they were concordant.

They observed postictal perfusion reductions of 415 units (ml/100 g/l) 15 of the 21 patients (71.4 percent). In 12 out of 15 (80 percent) of these patients, the location of the hypoperfusion was partially or fully concordant with the location of the presumed seizure onset zone.

The researchers compared the success of their technique to that of other neuroimaging modalities, finding that it was favorable: ASL offered better localization than structural MRI in 52 percent of cases; similar or better localization compared to ictal single-photon emission computed tomography (SPECT) in 60 percent of cases; and similar or better localization compared to interictal positron emission tomography (PET) in 71 percent of cases.

The results suggest that "this technique may be incorporated into the battery of conventional investigations for presurgical evaluation of patients with drug resistant focal epilepsy," the study authors concluded. If the findings are reproduced in larger studies, they added, the technique "might eventually be considered as a replacement for ictal SPECT in appropriately selected patients."

The researchers noted several limitations to their study. Among them, since only two of the patients studied had undergone surgery, the researchers could not use post-surgical outcomes to validate the findings; and because the EEG electrodes were removed approximately 20 min prior to each arterial spin labeling scan, it is possible that some electrographic seizures were missed during this period.

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