A method, system, and device for detecting whether an expandable member completely occludes an anatomic passageway allows a user, such as a physician, clinician, or surgeon, to perform a medical procedure more efficiently and increases the procedure's chances of success. An incomplete occlusion can be immediately detected by monitoring the pressure difference across the expandable member. Through this method, a user can quickly diagnose the problem and reposition the expandable member in the anatomic passageway. In particular, in a cryoablation procedure, devices incorporating this method can help ensure a uniform and complete lesion in the pulmonary vein to electrically isolate the pulmonary vein from the atrium, thus preventing atrial fibrillation.