Functional activation of the cerebral cortex creates a robust increase in local temperature by increasing blood flow and metabolism because of neurovascular coupling. 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 to create functional maps. 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 has 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 has high resolution (~100 micron) and simultaneously monitors the entire exposed brain surface without risk for seizures. The Intraoperative Mapping System will be developed and tested on glioma patients, as tumors have relatively static impact on brain temperature compared to epileptogenic foci and vascular malformations. Preliminary data in motor and language mapping cases shows large (~0.5oC) positive thermal activation of contralateral motor cortex and language regions that have strong agreement with DES.
Aim 1 will develop a mapping system (hardware and software) required to conduct real-time thermal-based brain mapping during awake craniotomy. We will optimize and integrate the infrared recording procedure within the surgical workflow, to maximize signal quality while minimizing treatment interference. The central piece is a mobile cart containing a powerful workstation and an articulating arm to locate the IR camera over the craniotomy. The computer will deliver stimuli, monitor and collect behavioral data (audio, video, and a wireless haptic glove), record the IR images, and display the real-time functional map. Patient tasks currently used during DES will be adapted for thermographic recording.
Aim 2 will explore the temporal and spatial properties of the thermodynamic response to optimize the infrared mapping procedure. The thermal response function (TRF) is the thermal equivalent of the hemodynamic response function (HRF) that is used in fMRI. Through modeling and high resolution (spatial and temporal) IR data, we will estimate the thermal impulse response and use it to develop an efficient multi-task mapping protocol. The result will be a rapid, efficient, high resolution assessment of brain function to optimize the resection and improve patient outcomes.
Aim 3 will compare the functional mapping methods (DES and infrared thermal imaging) to determine optimal synergy between them to provide the best information for the safest resection. If successful, this project will create a new method for intraoperative functional mapping during awake neurosurgery. Ultimately, we hope to improve the precision of intraoperative brain mapping while increasing the safety and efficacy of surgery for patients with drug-resistant epilepsy, glioma, and neurovascular malformations.
Due to neurovascular coupling, neural activity creates a reliable increase in blood flow and hence local temperature, which can be measured in the operating room with an infrared thermographic camera. While an awake patient performs tasks, this new method of monitoring the patterns of temperature fluctuation can be used to create a map of brain function, that once validated the surgical team can use to avoid damage to key functional areas. This can lead to safer, faster, and more effective surgeries for patients with drug-resistant epilepsy, glioma, or neurovascular malformations.
