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). The site of 11 tumors was clearly identified by low temperature (10 gliomas) or high temperature (1 cavernous angioma). In all patients, IR localization was consistent with the results of preoperative MRI, intraoperative ultrasound, and surgical findings. Although the region of tumor involvement could be distinguished clearly from the distant, normal brain, temperature heterogeneity occurred within the borders of individual lesions. Normal and tumor-related surface vessels greater than 0.5 mm in diameter and their dynamic temperature profiles reflecting focal pulsatile perfusion were visible on IR images. Functional localization of cortex was performed during median, tibial, and trigeminal nerve stimulation, repetitive motor task performance, and language testing. These stimuli produced reproducible, rapid latency (0.5-7 sec), topographically-restricted temperature gradients (0.04-0.08 deg. C) in the exposed cortex. Activated cortical sites with spatial resolution of up to 150 Tm were displayed on-line. The localization of these sites was consistent with localization by intraoperative electrophysiology. Thus, intraoperative IR imaging may enhance the accuracy and safety of tumor resections near eloquent cortex. Furthermore, 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.
