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FIGURE 28 3D volume rendering of CT scan in craniofacial surgery planning using mirror imaging to compute precise implants for placement in patients with anatomic defects.

[9,44,45,66]. Patients with cardiac arrhythmias can be treated with direct surgical resection of the heart muscle involved or by catheter-based ablation of the affected anatomic region using focused high-energy beams. A 3D image-guided procedure can provide detailed real-time four-dimensional anatomy and electrophysiology of a patient's heart to the electrophysiologist or the cardiologist in an interactive visual context during the ablation procedure. 3D views of the heart in motion can be created from any point of view inside or outside of the heart with progression of nerve activation signals shown as a continuous pattern of colors mapped onto the walls of the heart chambers. The displays can be created from a model consisting of time-varying dynamic geometry of the inner and outer surfaces of the beating heart, combined with time and spatially varying conduction field variables describing the dynamic electrophysiology activity at every point on the moving surfaces. Motion captured by the real-time ultrasound images from different orientations are registered to and used to deform the 3D heart model so it will closely approximate the specific global motions of the individual patient's heart during the procedure. The intracatheter electrodes are identified in the ultrasound images and localized globally on the heart model. Individualized digitized electrode signals are analyzed and used to produce a dynamic parametric display consisting of calibrated color values on the heart surface at each electrode location. The global mapping for each instance of the cardiac cycle can be computed by advanced piecewise interpolation algorithms along the surface between electrode positions.

Realistic and interactive real-time manipulation of the model can be accomplished using virtual reality display technology, such as head-mounted displays [44]. In such an immersive environment, the electrophysiologist or cardiologist will be able to view the dynamic three-dimensional visualization simply by moving his or her head around and through the model. This can all be accomplished in real time during the procedure. Figure 27 shows such an image-guided ablation procedure, wherein under visual guidance the catheter can be precisely positioned to point toward the offending region of tissue (left panel). The ablation can be accurately accomplished under such guidance, without the time-consuming "trial-and-error'' iterative sequence routinely used in this procedure. Following the ablation, normal rhythm is returned and can be observed by the same mapping technique (right panel).

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