Transplanted kidney. Coloured magnetic resonance imaging (MRI) scan of the abdomen of a patient that has had a kidney transplant. A contrast medium has been used to show the blood vessels. The aorta, the body's main artery, runs down centre and divides into the two iliac arteries that serve the legs. At centre right are the blood vessels serving the transplanted kidney. Transplantation replaces a failed or failing kidney with a donor kidney. The kidneys filter waste from the blood and excrete it as urine.