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FIGURE 16 Diagram of approach to virtual endoscopy using volume modeling.

FIGURE 16 Diagram of approach to virtual endoscopy using volume modeling.

FIGURE 17 Virtual endoscopic views within various anatomic structures within the body demonstrated on the Visible Human Male Dataset. See also Plate 120.

preoperative images for navigation needs to be calibrated carefully against this brain shift [38,67]. Intraoperative 3D imaging systems, like 3D MRI, are a potential solution to this problem, but they are still developmental, are very expensive, and are not generally available in most hospitals.

Current approaches to these problems provide real-time, online data fusion of preoperative high-resolution 3D multi-modality image scans of the patient with intraoperative video or ultrasound imaging of the patient during the surgical procedure. Patient-specific accurate models of the brain are computed from the preoperative MRI and CT scans, which can be accurately segmented and registered with advanced software. These patient-specific models can be projected onto realtime images of the surface of the patient's exposed brain during the operation, facilitating exact localization of underlying tumors or other pathology. This technique is sometimes referred to as augmented reality [12,29].

Figure 22 shows an example of data fusion in augmented reality. Volume rendered 3D images are registered with live video images in the operating room to reveal the deep-seated brain tumor. The location and position of tumors and vessels in relation to the brain surface can be visualized before resection begins.

In the near future, accurate segmented brain models will be deformed in real time in the operating room based on anatomic position information obtained from the patient while on the table. This may be provided by optical tracking or global positioning systems, video images focused on the actual operating site, and/or ultrasound scan images of the exposed cortical surface of the brain. This information influences the deformation of the brain model to ensure the correct shape, size, and location of the shifted brain within the cranium. A heads-up display system will allow the surgeon to view 3D models transparently through the surface of the cerebral cortex. Alternatively, the surgeon can be equipped with light head-mounted display equipment to look into the patient with supervision during the operation and to get immediate 3D visual update of the surgical field. This can be compared rapidly to preoperative planning and rehearsal images. Realtime measurements of size, shape, distances, volumes, etc., can

FIGURE 18 Segmentation, rendering, and endoscopic visualization of breast, mammary glands, and mammary vessels (top) and of ovaries, fallopian tubes, uterus, and bladder (bottom) from the Visible Human Female Dataset.

be provided to guide the surgery quantitatively. Projection of the segmented objects of interest within the surgical microscope will be most useful. The majority of the resection of the tumor will be performed under the guidance and improved visualization of high-quality surgical microscopes.

These exciting visualization procedures will enable more precise and expedient navigation to the target site and will provide more accurate delineation of margins for resection in brain surgery than current procedures. Importantly, the new procedures will provide on-line, updated information to accommodate any shifts in brain position during the operational procedure. This will result in significantly increased physician performance, reduction in time in the operating room, and an associated increase in patient throughput and decrease in health-care costs by comparison to current practice.

FIGURE 19 Segmented and texture mapped volume models of lungs and trachea with interior endoscopic view reconstructed from the Visible Human Female Dataset. See also Plate 121.
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