Inner and Outer Contours can be represented by two different techniques:

Using the "keyhole" technique, an ROI with an excluded inner part is represented with a single planar Contour. In this method, an arbitrarily narrow channel is used to connect the outer contour to the inner contour, so that it is drawn as a single contour. An example of such a structure is shown in Figure C.8.8.6-1 with the channel at roughly the 12 o'clock position.

Points in space lying along the path defined by the contour are considered to be part of the ROI.

Using the "XOR" technique, an ROI with an excluded inner part is represented by two planar Contours that are combined by a geometric exclusive disjunction, thus extracting the inner from the outer Contour, see Figure C.8.8.6-2. The contours have the Contour Geometric Type (3006,0042) CLOSEDPLANAR_XOR.

Using this technique, it is also possible to create an ROI that includes disjoint parts of the ROI within an interior void. When two or more Contours are present, two Contours are combined using a geometric exclusive disjunction ("XOR"). Then this result is combined by an XOR operation with a third Contour, and so on for all other Contours of this ROI. The order of combination does not matter. An example of the result of an XOR operation of three Contours is visualized in Figure C.8.8.6-3.