In vascular imaging, what does run-off describe?

• A. Proximal arterial inflow
• B. Venous return to the heart
• C. Perfusion of the distal arterial bed
• D. Collateral artery development

Answer: (C)

Run-off describes the perfusion of the distal arterial bed. It reflects how well blood reaches the downstream arteries beyond a lesion, such as the tibial and pedal vessels in the leg, indicating the quality of distal perfusion after upstream disease. A good run-off means blood can reach the farthest arteries, which supports successful restoration of flow with treatment. A poor run-off signals limited distal perfusion due to extensive disease or poor collateral channels, impacting prognosis and intervention decisions. This concept is different from proximal arterial inflow, which is the incoming flow before the diseased segment, and from venous return, which concerns the venous side. Collateral development can influence run-off, but run-off itself is specifically about distal arterial perfusion.