ROI events?

Hi,

Is there an event generated anywhere which I could use to test whether a region 
of interest has been moved or changed? Ideally i'd be looking for an event each 
time the ROI is moved or resized, I can't see an obvious way to do it at the 
moment, so I wondered if anyone else has done anything like this before or if 
anyone could suggest the simplest way to go about doing something like this?

Thanks