Abstracts

Rationale: Optical topography (=OT) is a noninvasive method for measuring regional cerebral blood volume (rCBV) change using near-infrared light. In conventional OT, the 30mm distance between light source and detector make it possible for the emitted light to reach the cerebral cortex, at a depth of approximately 20mm from the scalp. The maximum disadvantage of conventional OT is the low spatial resolution. To improve this shortage, we developed the double spatial density OT. In this study we will show two advantages of DD-OT. One is twice spatial resolution and the other is more stable measurement than the conventional OT. Methods: We developed the double spatial density OT by putting another pair of transmitting-sensor probe between original pair of probes, which make us possible to measure the rCBV by 1.5cm interval. Using the double density OT (DD-OT), we compared the spatial distribution of HbOxy change during motor, sensory and language stimulation with single density OT in 5 normal volunteers. With 3D-magnetic sensor, we superimposed the changes of rCBV onto the MRI surface images and evaluated the spatial resolution of both type of OT on it. To reveal the usefulness of DDOT for detecting epileptic focus, we performed rCBV by DD-OT on neocortical epileptic patients. Increasing area of rCBV measured by ictal DD-OT during phase1 monitoring were compared with epileptic focus detected by grid electrodes inserted on cortical surface in phase 2 monitoring. Results: The peak of rCBV changes by finger tapping and sensory task were showed on the motor cortex and sensory cortex, respectively, on the MRI surface image. The valley line of these two peaks of rCBV is identical to the central sulcus detected by MRI image. The results of ictal DD-OT of intractable neocortical epilepsy patient are also identical to the results of ictal EEG recording with the subdural grid electrodes. Conclusions: DD-OT showed more precise, fine and stable distribution of rCBV changes on MRI images during the task. DD-OT showed higher spatial resolution comparing with conventional OT and is useful for precise functional brain mapping or epileptic foci diagnosis.