Human intracranial high frequency oscillations (HFOs) detected by automatic time-frequency analysis.
OBJECTIVE
High frequency oscillations (HFOs) have been proposed as a new biomarker for epileptogenic tissue. The exact characteristics of clinically relevant HFOs and their detection are still to be defined.


METHODS
We propose a new method for HFO detection, which we have applied to six patient iEEGs. In a first stage, events of interest (EoIs) in the iEEG were defined by thresholds of energy and duration. To recognize HFOs among the EoIs, in a second stage the iEEG was Stockwell-transformed into the time-frequency domain, and the instantaneous power spectrum was parameterized. The parameters were optimized for HFO detection in patient 1 and tested in patients 2-5. Channels were ranked by HFO rate and those with rate above half maximum constituted the HFO area. The seizure onset zone (SOZ) served as gold standard.


RESULTS
The detector distinguished HFOs from artifacts and other EEG activity such as interictal epileptiform spikes. Computation took few minutes. We found HFOs with relevant power at frequencies also below the 80-500 Hz band, which is conventionally associated with HFOs. The HFO area overlapped with the SOZ with good specificity > 90% for five patients and one patient was re-operated. The performance of the detector was compared to two well-known detectors.


CONCLUSIONS
Compared to methods detecting energy changes in filtered signals, our second stage - analysis in the time-frequency domain - discards spurious detections caused by artifacts or sharp epileptic activity and improves the detection of HFOs. The fast computation and reasonable accuracy hold promise for the diagnostic value of the detector.
Neurosurgery Department, University Hospital Zurich, Zurich, Switzerland; Institute of Neuroinformatics, ETH Zurich, Zurich, Switzerland.
Sergey
S
Burnos
Swiss Epilepsy Centre, Zurich, Switzerland.
Peter
P
Hilfiker
Neurosurgery Department, University Hospital Zurich, Zurich, Switzerland.
Oguzkan
O
Sürücü
Biomedical Optics Research Laboratory, Neonatology Department, University Hospital Zurich, Zurich, Switzerland.
Felix
F
Scholkmann
Neurosurgery Department, University Hospital Zurich, Zurich, Switzerland.
Niklaus
N
Krayenbühl
Swiss Epilepsy Centre, Zurich, Switzerland; Neurology Department, University Hospital Zurich, Zurich, Switzerland.
Thomas
T
Grunwald
Neurosurgery Department, University Hospital Zurich, Zurich, Switzerland; Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
Johannes
J
Sarnthein
D000328:Adult; D016477:Artifacts; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D058256:Brain Waves; D004567:Electrodes, Implanted; D006801:Humans; D008297:Male; D008875:Middle Aged; D012640:Seizures / Q000175:diagnosis* / Q000503:physiopathology; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D013997:Time Factors