gms | German Medical Science

Introduction: Intraoperative optical imaging of intrinsic signals is a developing method for a fast and contact free visualization of stimulated eloquent brain areas during neurosurgical interventions. Local changes of the optical properties of the cortex based on cerebral blood volume changes during stimulation can be measured by detecting the reflected light from the cortex.

Material and methods: The intraoperative optical imaging system comprises a CCD camera with a digitalization of 12 bit mounted to a standard operation microscope and a xenon lamp connected via light fibre to the microscope. The incident light is passed through a narrow band interference filter (λ = 568 nm, FWHM = 10 nm). The optical imaging system was used in 72 patients with a tumor adjacent to the somatosensory, visual or speech cortex. Optical data acquisition lasted 9 minutes with alternating 30 s rest condition and 30 s stimulation condition. Activity maps were calculated as the difference of gray value intensity between the averaged images during stimulation and rest condition. Brain movements associated with heartbeat and respiration were compensated with an elastic registration algorithm.

Results: Localized activated areas of cortical tissue could be visualized for the somatosensory, visual and speech cortices. The calculated location of the activated areas corresponded to the anatomical landmarks and the results derived by electrophysiological examinations. In very few cases, no activation of cortical tissue could be detected because of technical and biological artifacts. In patients with neurological deficits, activity maps show only marginal activity. An excellent imaging quality could be achieved for most of the patients. The cortical activity maps were reproducible in independent examinations.

Conclusion: Intraoperative optical imaging provides two-dimensional maps of cortical activity with high spatial resolution. Overlaying the activity maps with an anatomical image of the cortex allows the localization of eloquent brain areas during surgery.

(The study is funded by the Carl Zeiss Surgical GmbH and BMBF.)