Abstracts

Rationale: Functional near-infrared spectroscopy (fNIRS) is one of the non-invasive functional brain mapping methods. The advantages of this method are its portability and higher tolerance for body movements. On the other hand, the largest disadvantage of fNIRS resides in its low spatial resolution. The spatial resolution of fNIRS is estimated to be 20mm to 25mm, making it difficult to detect the activated area as small as one gyrus-width, which is about 10-15mm. To overcome this problem we developed double density fNIRS (DD-fNIRS) probe design. For the patient with intractable epilepsy, an accurate diagnosis of the epilepsy focus is inevitable in order to get good outcome in a surgical intervention. For this purpose, we developed and investigated the utility of ictal DD-fNIRS recording as a new functional mapping technique in the presurgical diagnosis of epilepsy focus, especially in neocortical epilepsy.Methods: DD-fNIRS has special emitting and detecting optrode set. Two pairs of optrode sets (emitting optrode and detecting optrode separated in 30mm in conventional fNIRS) are placed overlapping each other where the optrode of the second pair is placed between the first one. This makes measuring points placed 15mm apart each other in place of 30mm apart in conventional design. In this study we used ETG 4000 (Hitachi Medical Corporation, Tokyo, Japan) for DD-fNIRS. Ictal video-EEG monitoring (VEEG) is the most reliable and important examination to diagnose epilepsy focus for the patient with intractable epilepsy. We have applied ictal DD-fNIRS simultaneously recorded with VEEG for two patients with neocortical intractable epilepsy. DD-fNIRS data has analyzed and superimposed with individual MRI image by 3D-magnetic digitizer.Results: Both patients had had operation of subdural electrodes placement for chronic subdural EEG recording after non-invasive pre-surgical examination such as ictal DD-fNIRS,VEEG, Iomazenil-SPECT (IMZ-SPECT) and magnetoencephalography (MEG). The epileptic focus diagnosed by ictal DD-fNIRS was quite similar to the lesion diagnosed by ictal subdural EEG recording. One patient has been already past more than three years after resection of epilepsy focus and no seizure has been described, another patient has been about 6 months after focus resection and seizure free.Conclusions: DD-fNIRS is useful to diagnose epilepsy focus for the patient with neocortical intractable epilepsy.