Comparison of the alignments of small metastatic nodules in the upper lung after deformable image registration. White arrows indicate small metastatic nodules in the left upper lung and subtle latent lesions in the right upper lung. (a) Columns from left to right are a moving image (left upper lung nodule diameter is 14 mm), fixed image (left upper lung nodule diameter is 10 mm), warped moving image (left upper lung nodule diameter is 13.6 mm), and subtraction image. (b), (c) Local enlarged subtraction images of the left upper lung nodule with six successive slices in the axial and coronal planes. Clear enhanced shadows are seen in the subtraction images. (d), (e) Local enlarged images of nodule with six successive slices and detailed comparisons of the morphological changes. In (d) and (e), the above row shows the nodule in moving images, while the below row shows the nodule in warped moving images. The nodule in the warped moving image retained nodular morphology when compared to that in the moving image.