Track visual changes of UIElement

Question

I have an adorner over UIElement (any UIElement) where I draw something based on visual content of UIElement (I use VisualTreeHelper.GetDrawing). It works perfect except UIElement is changing its visual representation (re-render itself). I desperatly need a way to know when something is changed on UIElement, like if we have UIElement.Rerendered or UIElement.VisualInvalidated... or the fast way to determine that UIElement's visual part is not the same as before.