Circle
To draw a circle on the image:
Click Annotate on the menu bar.
Click Circle 
.
Notes
The circle annotation can be created in all viewers except the 3D viewer.
The circle annotation line thickness can be chosen.
Click and drag on the image.
The circle is shown in the viewer and added to the Annotation tab 
on the SmartPanel under the group of Annotations. Click 
to change the color or delete the circle. To move the circle, click and drag the annotation on the viewer.