*4.3.3 Magnetoencephalography (MEG)*

MEG is a noninvasive functional neuroimaging method for investigating electrical neuronal activity of the living human brain by using sensors positioned around the head [38] that measure fluxes in the magnetic field caused by the same brain electrical activity, which is excellent for spatial and temporal resolution and is complementary to scalp EEG [38]. However, certain limitation for the wide use of MEG is due to signal disturbance caused by subject motion and the high maintenance cost [38].

### *4.3.4 Optic-magnetoencephalography (OP-MEG)*

This method functions through optic-pumped magnetometers and high Tc SQUIDs and does not require a thermal isolation [39]. It allows to move the subject naturally while recording long-term OP-MEG recording akin to EEG telemetry, which is especially useful in pediatric epilepsy [39].

### *4.3.5 Single photon emission computerized tomography (SPECT)*

This functional neuroimaging modality is based on a radioactive tracer, imaging hardware, and data analysis software. 99mTc-ethyl cysteinate dimmer [ECD or NeurolyteR ] or 99mTc-99 m HMPAO SPECT is used for measurement of regional cerebral blood flow in vivo [40]. Compared with 18F-FDG PET, brain SPECT has inferior spatial but superior temporal resolution, allowing identification of onset-zone and increased neuronal activity during the ictal phase, which is associated with increased metabolism and regional cerebral blood flow (RCBF) [40]. SPECT can also detect additional abnormalities in regions without structural abnormalities.

#### *4.3.6 Fluorodeoxyglucose positron emission tomography (FDG-PET)*

FDG-PET is an indirect marker of neuronal energy metabolism by measurement of glucose consumption. PET is obtained during the inter-ictal phase because cerebral uptake of FDG occurs over 30–40 minutes after injection and represents the imaging consumption of cellular metabolic process during the uptake period. The prolonged cerebral metabolic uptake makes FDG inappropriate for measuring rapid neural events considering the average seizure duration of 1–2 minutes; thus, ictal FDG PET is not usually feasible [40, 41]. Epileptogenic foci of inter-ictal TLE and extra TLE are associated with the area of reduced glucose metabolism that usually extends beyond the seizure-onset zone [30].

#### *4.3.7 Hybrid PET/MRI*

PET/MRI has shown improved diagnostic yields in detecting potential epileptogenic lesions in patients with refractory seizures presenting for possible epilepsy surgery [42]. The choice of tracer depends on the physiological process of interest such as oxygen consumption, glucose metabolism, or cerebral blood flow. The sensitivity

*Recent Advances in Epilepsy Surgery DOI: http://dx.doi.org/10.5772/intechopen.107856*

of detecting unilateral temporal lobe hypometabolism by inter-ictal FDG-PET/MRI is 70–80% [42].

#### *4.3.8 Non-FDG PET procedures (neurotransmitters)*

#### *4.3.8.1 Central benzodiazepine receptors*

Carbon-11-labeled Flumazenil (FMZ) is a specific reversible bound antagonist to the central benzodiazepine site on the GABAA receptor complex. GABA receptor binding and FMZ uptake are reduced in the epileptogenic foci, and the seizure onset zone has narrower distribution than the corresponding area of FDG hypometabolism. However, an area of focal decrease of FMZ uptake in the cortical regions remote from the primary focus may occur complicating localization of epileptogenic focus [43].

#### *4.3.8.2 Dopamine receptors*

Awareness of dopamine role in the pathophysiology of focal epilepsy is growing after the discovery of dopamine receptors (D1, D2, D3); D1 more pro-convulsant, and D2s have anticonvulsant effect [4, 44]. PET studies with the high affinity of D2/ D3 receptors radioligand 18F-fallypride have shown that D2/D3 receptor levels are significantly decreased in the epileptogenic temporal lobe in all patients, including the temporal pole and lateral temporal region in patients with TLE and hippocampal sclerosis, which inhibit decreased FDG uptake. These findings suggest that dopaminergic system is part of the endogenous anticonvulsant mechanism that prevents generalization of the seizure [44].

#### *4.3.8.3 Serotonin receptors*

PET radio-tracer 11C-α- methyl- tryptophan (AMT) is used for quantification of serotonin synthesis in the brain, which is increased in cortex epileptic area and reveals the epileptogenic focus in the inter-ictal state [44].

#### *4.3.8.4 Opioid receptors*

Functional imaging with PET radiotracers yields quantitative measurement of opioid binding mediated by μ, γ κ, opioid receptors. This has not demonstrated specific changes in TLE idiopathic epilepsy [4].
