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K.-Y. Jung
seizure-free by resection of brain region presumed to be epileptogenic zone. Since
epileptogenic zone cannot be measured directly, its location should be inferred indirectly by defining other zones including irritative zone, epileptogenic lesion, and
symptomatogenic zone, and functional deficit zone [35].
Presurgical evaluation for epilepsy include high-resolution magnetic resonance
imaging (MRI) scan and video-EEG monitoring. Functional neuroimagings such
as single photon emission tomography (SPECT) and positron emission tomography
(PET) are frequently used as ancillary tools especially in case of no discernible lesion
on brain MRI. Seizure onset zone (SOZ), or ictal onset zone, is the area of cortex from
which seizures are generated, which can be measured by noninvasive and invasive
EEG recordings. As epileptogenic zone involves SOZ, accurate localization of SOZ
is imperative for successful seizure control. Scalp EEG is noninvasive electrophysiologic test which helps to identify SOZ. However, the accuracy of scalp EEG for
localization or lateralization is reported less than 50% [18, 24, 26].
Invasive EEG recording using intracranial placement of electrodes such as depth
electrode, subdural strip and grid is necessary when discordant findings among
presurgical evaluations are present or epileptogenic zone cannot be determined by
surface EEG recording. Intracranial EEG provides much higher spatial information,
which is able to pick up potential changes occurring over only a few millimeters
of cortex. However, apart from invasiveness, the spatial sampling is restricted by
the number of electrodes, which may lead to fail to identify SOZ [37]. Despite the
invasiveness, localization of SOZ by intracranial EEG monitoring is still regarded as
a gold standard. Brain MRI technology is developing rapidly and has huge impact on
the diagnosis of various neurological diseases such as stroke, epilepsy, and dementia. It can provide us with high spatial resolution with accurate location and precise information about structural alterations in the brain. However, because of the
poor temporal resolution of MRI, it cannot tell much about information on rapidly
time-varying processes in the brain such as epileptic discharges and neurocognitive
processes.
Thanks to the recent advances in computer technologies, EEG in conjunction
with neuroimaging technologies have allowed us to extend its clinical utility for
the evaluation of patients with epilepsy [33]. Application of EEG source imaging
(ESI) and high frequency oscillation (HFO) for the presurgical evaluation have had
significant impact on the identification of epileptogenic zone and understanding
epileptogenesis. In this chapter, clinical utilities of ESI and HFO in the presurgical
evaluation of epilepsy will be discussed. I will review clinical trials or applications
of these techniques with relatively large samples, and discuss how these methods
contribute to the surgical treatment of epilepsy.
8.2 EEG Source Imaging
ESI is a model-based imaging technique that integrates temporal and spatial components of EEG to identify the sources generating electrical potentials recorded on
K.-Y. Jung
seizure-free by resection of brain region presumed to be epileptogenic zone. Since
epileptogenic zone cannot be measured directly, its location should be inferred indirectly by defining other zones including irritative zone, epileptogenic lesion, and
symptomatogenic zone, and functional deficit zone [35].
Presurgical evaluation for epilepsy include high-resolution magnetic resonance
imaging (MRI) scan and video-EEG monitoring. Functional neuroimagings such
as single photon emission tomography (SPECT) and positron emission tomography
(PET) are frequently used as ancillary tools especially in case of no discernible lesion
on brain MRI. Seizure onset zone (SOZ), or ictal onset zone, is the area of cortex from
which seizures are generated, which can be measured by noninvasive and invasive
EEG recordings. As epileptogenic zone involves SOZ, accurate localization of SOZ
is imperative for successful seizure control. Scalp EEG is noninvasive electrophysiologic test which helps to identify SOZ. However, the accuracy of scalp EEG for
localization or lateralization is reported less than 50% [18, 24, 26].
Invasive EEG recording using intracranial placement of electrodes such as depth
electrode, subdural strip and grid is necessary when discordant findings among
presurgical evaluations are present or epileptogenic zone cannot be determined by
surface EEG recording. Intracranial EEG provides much higher spatial information,
which is able to pick up potential changes occurring over only a few millimeters
of cortex. However, apart from invasiveness, the spatial sampling is restricted by
the number of electrodes, which may lead to fail to identify SOZ [37]. Despite the
invasiveness, localization of SOZ by intracranial EEG monitoring is still regarded as
a gold standard. Brain MRI technology is developing rapidly and has huge impact on
the diagnosis of various neurological diseases such as stroke, epilepsy, and dementia. It can provide us with high spatial resolution with accurate location and precise information about structural alterations in the brain. However, because of the
poor temporal resolution of MRI, it cannot tell much about information on rapidly
time-varying processes in the brain such as epileptic discharges and neurocognitive
processes.
Thanks to the recent advances in computer technologies, EEG in conjunction
with neuroimaging technologies have allowed us to extend its clinical utility for
the evaluation of patients with epilepsy [33]. Application of EEG source imaging
(ESI) and high frequency oscillation (HFO) for the presurgical evaluation have had
significant impact on the identification of epileptogenic zone and understanding
epileptogenesis. In this chapter, clinical utilities of ESI and HFO in the presurgical
evaluation of epilepsy will be discussed. I will review clinical trials or applications
of these techniques with relatively large samples, and discuss how these methods
contribute to the surgical treatment of epilepsy.
8.2 EEG Source Imaging
ESI is a model-based imaging technique that integrates temporal and spatial components of EEG to identify the sources generating electrical potentials recorded on