Apparatus, including a probe having a distal endinsertable into a nasal sinus of a human patient, and alocation sensor positioned within the distal end. Asinuplasty balloon is positioned on the distal end at aselected opening of the nasal sinus. A processor receivesfirst signals from the location sensor while the distalend is inserted into the nasal sinus and prior topositioning of the balloon at the selected opening, andgenerates a first map of the sinus. The processorinflates the balloon when it is at the selected opening,so as to enlarge the selected opening, and subsequentlydeflates the balloon. The processor then receives secondsignals from the location sensor and generates therefroma second map of the sinus. The processor registers thefirst map with the second map and generates from theregistered maps a numerical increase in size of theselected opening.
