A desired 2D image may not be parallel to any orthogonal orientation in which the 3D volume image was acquired, but is more likely to lie along an arbitrarily oriented plane at some oblique angle to the orthogonal axes of the volume image. Specification of the orientation and efficient generation of the oblique image require additional visualization and computation techniques [2,51,54]. Two methods can be used for definition of the oblique plane orientation. Selection of any three points or landmarks in the volume will uniquely define the orientation of the plane, which may need to be rotated within the volume for proper display orientation. Alternatively, two selected points define an axis along which oblique planes perpendicular to the axis can be generated. The oblique image may be generated anywhere along the axis — useful when a stack of oblique images needs to generated through a structure. Interactive manipulation of the oblique plane orientation may
be accomplished using aeronautical maneuver terms (i.e., pitch, roll, yaw) with angle increment specification and control buttons for each maneuver, as shown in Fig. 3. Interactive placement and orientation of oblique planes can be facilitated by superimposing a line on orthogonal images indicating the intersection of the oblique image with the orthogonal images, as also shown in Fig. 3. Another method is to depict the intersection of the oblique plane with a rendered surface image, providing direct 3D visual feedback with familiar structural features .
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