A method, device, and system for evaluating a vessel of a patient, and in particular the hemodynamic impact of a stenosis within the vessel of a patient. Proximal and distal pressure measurements are made using first and second instrument while the first instrument is moved longitudinally in the vessel and the second instrument remains in a fixed position. A series of pressure ratio values are calculated, and a pressure ratio curve is generated. The pressure ratio curve may be output to a display. One or more stepped change in the pressure ratio curve are identified using an Automatic Step Detection algorithm. An image is obtained showing the position of the first instrument within the vessel that corresponds to the identified stepped change. The image is registered to the identified stepped change in the pressure ratio curve. The image may be output to the display.