Visualization to preoperatively assess and guide surgical operations has been used successfully and increasingly over the past two decades [3,15,25,29,49,58,59,60,74].

Neurosurgery has benefitted from and in turn significantly driven this evolution more recently [2,10,33,38,46,63,67].

Neurosurgery is a complex procedure, involving extended knowledge and understanding of intricate relationships between normal anatomy and pathology. Patients with brain tumors, arterial venous malformations, or other complicated internal brain pathology undergo multimodality image scanning preoperatively to help the neurosurgeon understand the anatomy of interest. Different scans can be coregistered in order to produce single visualizations of complementary information. Specific anatomical objects may be identified and segmented. The surgeon then can use this information to plan more carefully the surgical approach and determine the margins of pathology with respect to cerebral vasculature and eloquent cortical tissue.

Figure 21 shows an example of multimodal imaging, registration, and data fusion for visualizing brain anatomy and planning surgical resection of diseased tissue causing seizures in an epilepsy patient. CT scans are used to reconstruct the skull surface and subdural electrodes placed on the brain to

FIGURE 15 Volume modeling with texture mapping and deformation to simulate tissue cutting. See also Plate 119.

identify the motor strip. MRI is used to reconstruct the cortical brain surface, and SPECT is used to image the region of activation produced by injection of a radioisotope shortly after a seizure. All images are registered together, and the surgical plan can be developed from sequences of visualizations of the registered data as indicated in Fig. 21. The preferred location of the burr hole opening, localization of the offending tissue, the margins of eloquent adjacent functional tissue, and the most effective resection margins can all be preoperatively planned from such visualizations.

It is not routine that these imaging procedures provide sufficiently high-resolution, three-dimensional images or that they provide the intricate detail of anatomic relationships required to optimize the surgical procedure, that is, to determine the best approach and precise margins for effective resection of a tumor or repair of a vascular fistula. Furthermore, during the neurosurgical intervention, the brain itself changes position, shifting as the skull and dura are opened. Therefore, the brain is not in the same location as it was during the preoperative imaging procedure. The use of

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