Arterial spin labeling: Adaptive thresholding for epileptogenic zone detection in MRI-negative epilepsy

Drug-resistant epilepsy is a diagnostic and therapeutic challenge, mainly in patients with negative MRI findings. State-of-the-art imaging methods complement standard epilepsy protocols with new information and help to epileptologists to increase reliability of their decisions. In this study, we investigate if arterial spin labeling (ASL) perfusion MRI can help localizing the epileptogenic zone (EZ). To that end, we developed an image processing method to detect the EZ as an area with hypoperfusion relative to the contralateral unaffected side, using subject-specific thresholding of the asymmetry index in ASL images. We demonstrated three thresholding criteria (minimal product criterion, minimal distance criterion, and elbow criterion) on 29 patients with MRI-negative epilepsy (age 32.98 ± 10.4 years). The minimal product criterion showed optimal results in terms of positive predictive value (mean 0.12 and 0.22) and true positive rate (mean 0.71 and 1.82). Additionally, we found high accuracy in determining the EZ side (mean 0.86 and 0.73 out of 1.00). In conclusion, the ASL can be easily incorporated to the standard presurgical MR protocol and it provides an additional benefit in EZ localization.