A system for evaluating a vessel of a patient, comprising: an intravascular instrument sized and shaped for introduction into the vessel of the patient; and a processing system configured to be in communication with the intravascular instrument, an external imaging system, and a display, the processing system configured to: obtain intravascular data obtained by the intravascular instrument while positioned within the vessel of the patient and moved longitudinally through the vessel from a first position to a second position; obtain an angiographic image of the vessel obtained by the external imaging system as the intravascular instrument is moved longitudinally through the vessel; correlate the intravascular data from the intravascular instrument to locations on the angiographic image; and output an enhanced angiographic image of the vessel on the display, the enhanced angiographic image including the angiographic image overlaid with visualizations representing the intravascular data at the correlated locations; wherein the intravascular data is a pressure measurement; characterized in that the visualizations include a representation of a calculated pressure ratio; wherein the processing system is configured to identify transition points where a pressure ratio between portions of the vessel changes by a threshold amount and to indicate the transition points by markings on the angiographic image. an intravascular instrument sized and shaped for introduction into the vessel of the patient; and a processing system configured to be in communication with the intravascular instrument, an external imaging system, and a display, the processing system configured to: obtain intravascular data obtained by the intravascular instrument while positioned within the vessel of the patient and moved longitudinally through the vessel from a first position to a second position; obtain an angiographic image of the vessel obtained by the external imaging system as the intravascular instrument is moved longitudinally through the vessel; correlate the intravascular data from the intravascular instrument to locations on the angiographic image; and output an enhanced angiographic image of the vessel on the display, the enhanced angiographic image including the angiographic image overlaid with visualizations representing the intravascular data at the correlated locations; obtain intravascular data obtained by the intravascular instrument while positioned within the vessel of the patient and moved longitudinally through the vessel from a first position to a second position; obtain an angiographic image of the vessel obtained by the external imaging system as the intravascular instrument is moved longitudinally through the vessel; correlate the intravascular data from the intravascular instrument to locations on the angiographic image; and output an enhanced angiographic image of the vessel on the display, the enhanced angiographic image including the angiographic image overlaid with visualizations representing the intravascular data at the correlated locations; wherein the intravascular data is a pressure measurement; characterized in that the visualizations include a representation of a calculated pressure ratio; wherein the processing system is configured to identify transition points where a pressure ratio between portions of the vessel changes by a threshold amount and to indicate the transition points by markings on the angiographic image. <EOS>