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Figure 2. A more unusual application is registering images of knee joints for the purpose of tracking changes in the thickness of cartilage. The knee is particularly difficult to image consistently in three dimensions on consecutive occasions due to the high degree of mobility around the joint regardless of any disease process. Non-rigid registration, in this case using B-spline based free-form deformations, can recover most of the differences between scans of the same subject acquired at different times.
