Intraoperative functional mapping using infrared thermography

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PROJECT SUMMARY Functional activation of the cerebral cortex creates a robust increase in local temperature by increasing blood flow and metabolism. Changes in surface brain temperature while an awake patient performs a motor, sensory, or language task can be used to infer spatial patterns of activity. Awake neurosurgery is used in the management of drug-resistant epilepsy, glioma, and neurovascular malformation, in order to localize seizure and/or physiologic activity. Protection of key functional areas is imperative to avoiding postoperative neurologic deficits. Currently, direct electrical stimulation (DES) is the most commonly used method of intraoperative surgical mapping, which identifies functionally critical brain regions so they are not resected. However, DES is low spatial resolution (~1 cm), may provoke seizures, and can only test one area at a time. This project investigates a new method of intraoperative functional mapping based on infrared thermography, which is high resolution (~100 micron) and simultaneously monitors the all exposed brain regions without risk for seizures. The device will be tested on the rodent whisker barrel cortex following awake craniotomy. Subsequently glioma patients will be studied, as tumors have relatively static impact on brain temperature compared to epileptogenic foci and vascular malformations. Preliminary data in a motor mapping case shows strong thermal activation of contralateral motor cortex, and strong agreement with DES. Aim 1 will establish the thermal signature of cortical activation during awake craniotomy. We will optimize the infrared recording procedure within the surgical workflow, as to maximize signal collection and quality while minimizing treatment interference. A mobile tripod will stabilize the infrared camera, which is connected to a laptop computer. The computer will monitor and collect behavioral data via adjunct surgical devices. Patient tasks currently used in DES will be adapted for thermographic recording. Aim 2 will leverage the high temporal resolution of infrared thermography for mapping brain networks. Independent components analysis will decompose the thermal activity into discrete, independent patterns which correspond to brain networks. The connectivity patterns of these regions may be analyzed to extract phase information. Features of the network activation signal will then be tested for predictive value of DES outcomes. If successful, this project will create a new method for intraoperative functional mapping during awake neurosurgery. Future work will integrate preoperative functional mapping information into the thermal mapping procedure. Ultimately, we hope to improve the precision of intraoperative brain mapping, in order to increase the safety and efficacy of surgery for patients with drug-resistant epilepsy, glioma, and neurovascular malformations.