Prevent scrapping certain file types

Hi all, this is my first post on this forum.

I have converted my movie files in many differant file formats so that I can watch certain ones on differant devices. I end up with duplicated movies which are encoded differently.

So my movie collection is structured like this:

/movies/Movie A/Movie A.iso
/movies/Movie A/Movie A.mkv
/movies/Movie A/Movie A.avi

/movies/Movie B/Movie B.iso
/movies/Movie B/Movie B.mkv
/movies/Movie B/Movie B.avi

Is there anyway to restrict xmbc from scanning iso and avi files?
I don't want dups in my library.

Thanks