gms | German Medical Science

Introduction: During neurosurgical procedures, it is of great importance that functionally relevant areas of brain cortex are clearly identified to protect them from damage. So far, no intraoperative imaging techniques have been established that detect active cortical areas. Thermography, which is based on measuring the infrared radiation of an object, is a safe, non-invasive, label-free technique with a long history of use in medicine. In the exposed brain cortex, surface temperature correlates to perfusion. It may be possible to identify pathological areas of variable perfusion, such as ischemic areas or hyperperfused tumor areas. As neuronal activity is coupled to an increased tissue metabolism which, in turn, causes an increase in cerebral perfusion, even functionally active cortical areas could be identified by detecting an increase of temperature on the cortical thermal map during stimulation. In our study, we tried to evaluate the potential use of infrared thermography in brain surgery.

Material and methods: In over 100 neurosurgical procedures including brain tumor removal, decompressive craniectomy and epileptic focus resection, sequences of thermal images of the exposed cortex were recorded. A highly-sensitive digital infrared camera was used to image cortical temperature distribution after craniotomy and exposure of the brain. The camera has a spectral range of 7,5–14 µm that corresponds to a thermal range of –40 to 1200°C, it reaches thermal resolution of 0,03K at 30°C and a spatial resolution of 150 µm per pixel at minimum distance. Preprocessing and multivariate data analysis was performed on thermal image data using the MATLAB package. The recorded thermographic images were matched to preoperative radiological images using Brainlab and Amira software applications.

Results: In craniectomies performed in patients with malignant stroke, areas of reduced cortical temperature that corresponded to radiographically detected infarct areas were identified. In cases where the primary sensory area in the postcentral gyrus was exposed, a thermal activation of the sensory cortex hand area was detected during median nerve stimulation. During awake craniotomies with intraoperative speech mapping, temperature in the basal motor cortex as well as the Broca region increased during speech tasks. After a 50 ml bolus of cold saline was applied through a central line, a short decrease in temperature that temporally correlated with the injection was measured in cortical vessels.

Conclusion: By using time-resolved intraoperative thermographic imaging of the brain cortex, we were able to detect functionally active cortical areas such as somatosensory and motor cortex and speech region. Thermic contrast between tumors and healthy tissue was found but overlying normal and infiltrated tissue requires further investigations for determining tumor borders. As cortical temperature in stroke correlated to perfusion status shown by CT and CTA, it may be possible to identify and delineate infarcted and critically perfused regions. Overall, infrared thermography proved to be a safe and useful intraoperative imaging tool that may increase the safety of neurosurgical procedures.