It is important during neurosurgical procedures to identify and preserve eloquent functional cortex adjacent to a resectable lesion. Intraoperative real-time functional mapping techniques now available cannot be used in many surgical situations and are not sufficiently reliable in all cases in which they are used. We are examining an intraoperative approach that may permit lesion localization and brain functional mapping on-line with minimal risk. This approach makes use of infrared (IR) technology to identify functionally active cortex and may enhance differentiate abnormal tissue from normal cortex. The method is based on an analysis of the spatial and temporal dynamics of cortical temperature changes obtained by recording the intrinsic cortical IR radiation (3-12 Tm wavelength band). To use the IR method most effectively in humans, we validated it in an OR situation. Rhesus monkeys were used to examine localization of the somatosensory cortex. An IR camera (sensitivity 0.01 degr.C; 3-5( wavelength) was positioned 10 cm above the exposed cortex. Difference maps (stimulated minus control) defined topographic thermal features of the distribution of cortical activity. Physiological motion artifacts were reduced via gating and digital motion correction. Median nerve stimulation was used to evoke IR and high-resolution ECoG maps (3.5 mm inter-electrode distance) of monkey somatosensory cortex were obtained intraoperatively to validate the coordinates and accuracy of the IR functional localization. Statistical analysis of single trials (Z-score test) reveals well-defined and reproducible temperature gradients in somatosensory primary cortex and motor cortex. ECoG maps of the involved cortex revealed that the IR signal accurately delineated the area of activated cortex. The mechanism of IR activation was explored by examining IR changes during systematic occlusion of cortical arteries. In experiments with temporary applied to different cortical vessels aneurysm clips we found that blood flow changes had a significant effect on the IR signal: local temperature decreased in area of vessel occlusion and multifocal temperature increases occurred in another areas. Collateral flow was evaluated, and cortical """"""""steal"""""""" was observed in a collateral vessel during reperfusion. Use of high-resolution, digital IR imaging permits real-time visualization of arterial flow and has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion, and of directly visualizing flow in the parent arteries or persistent filling of an aneurysm after clipping, during surgery. We are also examining the IR camera during surgery of the exposed brain in humans. In 27 human cases with brain lesions (24 with tumors, 1 with CNS infection, and 2 patients with extractable epilepsy) infrared (IR) mapping of the cerebral cortex was performed at background and during functional activation. Activation paradigms included median nerve stimulation, hand movements, and speech/language production. Discrete temperature gradients were found associated with surgically-verified lesions in all cases. All oligodendrogliomas and glioblastomas tumors were colder than surrounding cortex. Metastatic lesions, cavernous angioma, a CNS infection site, as well as cortical sites with identified epileptiform discharges and interictal activity were hotter than surrounding cortex. Functional stimulation revealed cortical activation patterns in the form of evoked temperature gradients with a spatial resolution of 150 um. Neural activation elicited reproducible, rapid (latency 0.3-7.0 sec), focal temperature changes (0.04- 0.08 degr.C) in the primary somatosensory and motor cortex during repetitive hand movements and median nerve stimulation. Language production activated temperature changes in areas subsequently identified by cortical stimulation mapping as functionally significant for language/speech. Additional cortical areas were also activated, suggesting their involvement in the complex cognitive aspects of language/speech production. Use of high-resolution, digital IR imaging permits real-time visualization of arterial flow and has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion, and of directly visualizing flow in the parent arteries or persistent filling of an aneurysm after clipping. This method also may provide intraoperative, accurate, real-time functional mapping of the cortex for intraoperative neuro-navigation.Further, development of this IR imaging technique may permit successful visualization and localization of functional cortical areas during surgery and lead to new approaches to study neurophysiology in vivo.
