Medical scans such as Magnetic Resonance (MR) and computed tomography (CT) are currently common diagnostic tools in surgical applications. The intensity value at a given voxel of a medical scan is primarily a function of the tissue properties at the corresponding point in space. Typically, various anatomical structures appear more clearly in different types of internal scans. Soft tissue, for example, is imaged well in MR scans, while bone is more easily discernible in CT scans. Blood vessels are often highlighted better in an MR angiogram than in a standard MR scan. Figure 1 shows three different acquisitions of MR scans. Notice that some anatomical structures appear with more contrast in one image than in the others. Anatomical structures in these various modalities can be segmented and displayed separately. However, it is most convenient for the surgeon to have information about all the structures fused into one coherent dataset. To perform the multi-modality fusion, the different volumetric images are automatically registered to a single coordinate frame.
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