Intraoperative optical imaging (IOI) is a method to visualize functional activated brain areas during brain surgery using a camera system connected to a standard operating microscope. Three different high-resolution camera systems (Hamamatsu EB-CCD C7190-13W, Hamamatsu C4742-96-12G04, and Zeiss AxioCam MRm) have been evaluated for suitability to detect activated brain areas by detecting stimulation-dependent blood volume changes in the somatosensory cerebral cortex after median nerve stimulation. The image quality of the camera systems was evaluated in 14 patients with tumors around the somatosensory cortex. The intraoperative images of the brain surface were continuously recorded over 9 min. With all three camera systems, the activity maps of the median nerve area could be visualized. The image quality of a highly sensitive electron-bombarded camera was up to 10-fold lower compared with two less sensitive standard cameras. In each IOI-positive case, the activated area was in accordance with the anatomical and neurophysiological location of the corresponding cortex. The technique was found to be very sensitive, and several negative influencing factors were identified. However, all possible artifacts seem to be controllable in the majority of the cases, and the IOI method could be well adapted for routine clinical use. Nevertheless, further systematic studies are needed to demonstrate the reliability and validity of the method.