detect if a container has a loaded image inside

Hi guys,
I have a biiig problem.
I have a var mcLoader=new MovieClipLoader().
mcLoader.onLoadInit has a function asgined to it. The thing is I will use the mcLoader to load multiple images in multiple holders using the loadClip method (mcLoader.loadClip("image.jpg", holder_mc).
My question is how can I make flash detect whether a specific holder_mc has already an image loaded in it?
Thanks guys :)