1. A method, comprising: obtaining first volumetric image data, which is acquired at a first time, including a region of interest of a subject, wherein at least one structural feature in the region of interest is located at a first position in the first volumetric image data; creating a contour for the at least one structural feature on the first volumetric image data, wherein the contour identifies the at least one structural feature; obtaining second volumetric image data, which is acquired at a second time, including the region of interest of the subject, wherein the at least one structural feature in the region of interest is located at a second position in the second volumetric image data, wherein the second time is subsequent to the first time, and the first and second positions are different positions; adding a direction guideline to the first volumetric image data adjacent to the contour; determining a registration transformation that registers the first and second volumetric image data such that the at least one structural feature in the first volumetric image data aligns with the at least one structural feature in the second volumetric image data, wherein the registration transformation propagates the contour from the first volumetric image data to the second volumetric image data based on a combination of an estimated direction of a maximum slope of the contour in gray levels and the direction guideline; and generating a signal indicative of the registration transformation.