Renal angioplasty. Coloured X-ray angiograms of a balloon catheter being placed in the right renal artery of a 57-year-old patient. The image at top left shows stenosis (narrowing) of a renal artery (lower left). The top right image shows the balloon catheter (white, over spine) being guided into place by a flexible catheter (white line). Once in place it is inflated to open the artery and restore normal blood flow (bottom left image). A stent, a wire mesh tube, is inflated by the balloon. This remains in place after the catheter is removed, keeping the artery open (bottom right image). The most common cause of stenosis is atheroma, fatty deposits that thicken the inner coat of the arteries.