Calculating intern perimeter with regionprops?

Hey there,

I need help with my Final Thesis. I have lots of medical binary images. I need to calculate some measures that are important for doctors. I am using regionprops, because the Region Of Interest in the images is white, while the background is black, so regionprops will calculate the measures of the ROI. The big challenge appears when a picture has an intern contour. Imagine a ring, so it has an extern contour and also an intern contour. I have some images with this shape and I don't know how to calculate some measures such as perimeter. Regionprops will calculate the extern perimeter, but not the intern one. Do you have any idea about how I could do that? It is very important, I beg you to help me if you know how to do that.

Thank you very very very much for your attention.

Best regards,

Eva.