Official international guidelines for surveillance in patients with ulcerative and Crohn's colitis advise to take 4 random samples of large bowel tissue (biopsies) every 10 centimeters and of any suspicious areas. Recent studies have shown that spraying dye such as indigo carmine (a type of food dye) helps highlight abnormal areas that could harbor pre-cancerous cells. This technique is time-consuming, and tedious. There are no set standards of what is considered a satisfactorily completed dye spray colonoscopy. The uptake of this technique in the UK has not been uniform. Therefore virtual chromoendoscopy has been studied as an alternative method to improve the detection of pre-cancerous tissue in patients with longstanding colitis.