gms | German Medical Science

Objective: Optical imaging of intrinsic signals is a new method for a fast and contact free visualization of stimulated eloquent brain areas during neurosurgical interventions.

Methods: The intensity of the light reflected by the cortical tissue was measured in 18 patients with lesions around the somatosensory, visual or speech cortex using three different high resolution cameras (Hamamatsu Photonics: EB-CCD C7190, C4742-96 and Zeiss AxioCam MRm) mounted to an operating microscope. Using adequate stimulation methods the difference in the spectral absorption was used to differentiate between activated and non-activated brain areas. The data acquisition time was 9 minutes with alternating 30 seconds with and without stimulation. The difference between averaged frames was calculated and overlaid over an image of the operative site. Brain movements associated with heartbeat and respiration were compensated using a deformable registration algorithm.

Results: In 9 of 18 patients the intraoperative numerical analysis of the acquired image data sets showed a localized activation of cortical tissue. In 6 patients an excellent imaging quality could be achieved. The calculated location and the size of the activated region corresponded to the results derived by electrophysiological examinations and confirmed the estimation of the neurosurgeon. Most successful were the stimulations of the somatosensory and visual cortex. In 9 patients no activation of cortical tissue could be deciphered because of technical and biological artifacts.

Conclusions: Optical imaging of intrinsic signals provides an intraoperative high spatial resolution image of brain surface activation, allowing the localization of eloquent brain areas during surgery. Interestingly, the type of pathology seems to influence the perfusion of the surrounding tissue, so that changes between activation and rest may not be detectable in some cases.