Illustration of the semi-rigid model with three retained structures, where and are defined as translation and rotation respectively, for structure .
Diagram of the registration system.
Cross-sectional images exemplifying registration results for the physiologically-based simulated transformation for a simulated nodule. (a) Nodule (half major axis of the largest ellipsoid: ) in source volume. The two white rings surround cross-sections of the two principle structures extracted for this example. (b)–(f) Target volumes. (b) Nodule maintains size and shape. Distance error was . (c) Nodule disappears. Distance error was . (d) Nodule grows uniformly by a factor of 2. Distance error was . (e) Nodule shrinks uniformly by a factor of 2. Distance error was . (f) Nodule grows nonuniformly. Distance error was .
Experimental initial registration errors: (a) Ten simulated nodules. (b) Histogram of initial registration errors for the 97 nodules in the patient experiments.
Mean and its 95% confidence interval of the distance errors between our method and a rigid registration method for (a) simulated nodules and for the (b) real patient experiments as a function of cube side .
Mean distance error and its 95% confidence interval as a function of parameter settings. (a) Error versus minimum retained value, , with threshold , as parameter. (b) Error versus threshold, , with minimum retained value, , as parameter. Error as function of (c) number of structures , (d) nodule weight , (e) elastic energy weight , and (f) search range , respectively.
The outlier when . Left: Nodule (encircled) in segmented source volume. Right: Nodule (encircled) in the target volume that grew uniformly by a factor of 2 in the segmented target volume, which became contiguous with the chest wall.
An example of nodule in contact with blood vessel in one of the pairs of actual patient scans. (a) Source image. (b) Target image. Registration distance error for this nodule was .
Segmentation steps (from left to right): Portion of original image, showing juxtapleural nodule in center. Left lung contour excludes nodule. Edge closing using line segment test. Portion of segmented lung with nodule included.
Results for the simulated nodules.
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