Thanks for the reply! I have a couple different ROIs set up and I am measuring the amount of space inside the box that the "white stuff" occupies. (see the image below) I was a little vague about how I am actually doing the thresholding. In short, I am not just using the threshold vi and hoping for the best. I am trying to use an algorithm (using the Gaussian mixture model) that dynamically changes but like you said, with the lighting/contrast/brightness of the image always changing it does not always perform that well, whereas the edge detection seems to always find the correct edges.
I suppose I was hoping I could use the edge detection as the base for some kind of mask or something...