You can define more than one VOI shape in the volume, then have the application interpolate between the shapes drawn.
1. From the Tissue Definition toolbar, click VOI 
.
2. Select a VOI shape (oval, square, or freehand).
3. Scroll the reference images to the beginning of the region you want to define.
4. Click once to draw the shape you want, then double-click to end drawing.
5. Select a second region of interest at a different location in the volume.
The regions interpolate from one shape to the other as you scroll through the reference images.
NOTE: There is no limit to the number of VOIs you can draw.