MODEL RELEASED. Cardiology technician checking monitors of a patient's vital functions during a cardiac catheterization operation (in theatre through window). Cardiac catheterization provides a means of investigating blood flow within the coronary arteries, to check for the presence or extent of coronary artery disease. To do this, a catheter (a fine tube) is inserted into an artery and guided (using X-ray imaging) towards the heart. Once in place, an iodine-based dye is injected to outline the arteries on X-ray film, and locate any obstructions due to the formation of atheroma plaque. Model: Stephen Charlton