You can draw a curve on an image to measure the length in millimeters of the curve. You can also manipulate a curve by changing one or more of its vertices (handles) without having to draw a new curve. The graphic is added automatically as a bookmark. Open the Bookmark list to see its details.
1. From the Viewer, select an image.
2. In the Graphics tab of the toolbar, click Curve Measurement 
in the Measurements ribbon.
3. Click the location where you want to start the point of the curve.
A vertex (handle) appears at the selected point.
4. Click additional points, one after the other, to draw the curve.
Additional vertices appear at each point you click.
5. Double-click the last point to end the curve.