A system provides a display image enabling a user to visualize and compare blood flow characteristics over time at selected points in an angiographic X-ray image. A system and user interface enables user interaction with a medical vessel structure image to determine individual vessel blood flow characteristics. The system includes a user interface cursor control device and a display processor for generating data representing a single composite display image. The composite display image includes, a first image area showing a patient vessel structure and contrast agent flow through the patient vessel structure over a first period of time and a second image area showing a graph of contrast agent concentration in a particular portion of the vessel structure over a second period of time. The particular portion of the vessel structure is selected in response to user command using the cursor control device.
