To prevent blood flowing back after each heartbeat. They ensure that the blood flows only in one direction (back to the heart).
The procedure is called renal angiography. This procedure is done to check the quality of blood flow to the kidneys, check for blockages, narrowing of the blood vessels and lastly aneurysm. A dye is usually injected into the arteries for easier visualization.
Answer: I think it id b But im not positive
