a method and apparatus to treat barrett &# 39 ; s tissue , a pre - cancerous condition , by removing the epithelium above the lower esophageal sphincter through cryo - ablation . an endoscope with fiber optics is used to view the operation , and a catheter for supplying liquid nitrogen is passed through the lumen of the endoscope . liquid nitrogen at low pressure is sprayed directly onto the barrett &# 39 ; s tissue through the catheter while the physician views the operation through the fiberoptics of the endoscope and controls the spray via a valve . freezing is indicated by whiteness and shows that the epithelium has been cryoablated . the apparatus can also be used to treat various other gastrointestinal tract lesions . the catheter is insulated to withstand extremely cold temperatures without becoming stiff and without affecting the inherent flexibility and maneuverability of the endoscope .