A method and system for use with an endoscopic instrument determines anatomical properties of body lumen at various states. Lumen properties such as lumen diameter are identified in two or more states corresponding to, for example, an inflated or deflated state. The lumen states are registered with one another and the anatomical properties are identified in real time at the location of an endoscope or endoscopic instrument used with the endoscope. In one embodiment a diametrical range of an airway is identified in real time at the location of a bronchoscope.