How to crop an image using a circle

I need to crop an image from a rectangle to a circle. It seems the CLIPIMAGE command is the way to go, but after I Create boundary, I can't select the circle I've already drawn over the image as my Polyline to perform the crop.

If I can't use a circle to perform the crop, is there a way convert a circle to a polyshape that would work for my need?

[EDIT]

I've discovered that the POLYGON command works for this since I can create a polygon with say 1,000 segments with a center and side. This works perfectly for what I need to do.

 

- Kyle