How to determine if the curve is closed?

Hi all,
I want to find the markers in CT scout. Is it possible to determine if the curve is closed?

Which markers? What curve? Please provide more details.

Thanks.
The application is surgical navigation. The marker is made from round aluminum sheet. The marker is like a circle in the CT scout. I want to find them from the scout. I used the Canny Edge detection method. It found many curves. Among the curves, the closed curve I thought is the marker. So I want to know is it possible to determine if the curve is closed ? Or maybe are there any better segmentation methods to find the marker ?

Hough transform might be of interest to you. ITK’s implementation is called HoughTransform2DCirclesImageFilter.