“…Thus, 4D-CT is often contaminated by motion artifacts which include motion blur, overlap and gapping. [27][28][29] Although the motion-related artifacts could be reduced by the breath training, 30,31 improved sorting method, 1,29,32,33 utilization of internal anatomical features, 25,34,35 and postimage processing on 4D-CT images, 16,36,37 the interslice thickness (e.g., 3 mm), which is often much higher than the intraslice resolution (e.g., 1 mm), still remains as a big challenge in 4D-CT registration. Often, vessels become discontinuous across neighboring slices, which makes it difficult to perform reasonable registration especially for small vessels.…”