The functional Near-infrared spectroscopy (fNIRS) is the non-invasive imaging technique of the changes of cerebral blood volume. The instrument of fNIRS is compact and easy to handle, therefore it is widely used in neuroscience research and clinical diagnosis. Because it is the non-invasive measurement system, there is the limitation of improving the spatial resolution and of the reducing artifacts of skin or skull. In clinical, measurement technique of hemodynamics directly from the brain surface during the craniotomy surgery is required.
We developed functional Near-infrared Cortical Imaging (fNCI), which enables the measurement of cortical hemodynamics directly from the brain surface. The optodes were arranged at 5 mm apart.
We measured fNCI from the cortical surface of three Mexican hairless pigs. Under general anesthesia, the craniectomy was performed to expose the primary sensory cortex (the rostral region). The electrical stimulations were applied to the nostril, and somatosensory-evoked potential (SEP) and fNCI were recorded simultaneously. The spatial coordinates of measurement points of SEP and fNCI were positioned by use of the frameless navigation system which is customized for the pig's skull morphology. We stimulated the three different points of pig's nostril skin. The active points of SEP, fNCI(oxy-Hb, deoxy-Hb, total-Hb) were changed within the rostral region by the changing of stimulating points.
Our new technique can measure the cerebral activities directly from the cortical surface with higher spatial resolution than that of the transcranial fNIRS. This study provides a clue for investigating the theoretical and technical principles of NIRS and possible application of our technique for direct cerebral blood flow monitoring during the human brain surgery.