This research study will evaluate the safety and effectiveness of PDT with porfimer sodium using a new diffusing balloon device for light application in the removal of high-grade dysplasia (HGD, precancerous change in the food pipe tissue) in Barrett's esophagus (BE). This study will provide advanced knowledge about phototoxicity (reaction similar to sunburn) and esophageal stenosis, main risks with this therapy. It will involve 75 patients with HGD in BE across North America and Europe and will last between 13 and 16 weeks. In addition, concentrations of porfimer sodium in the esophageal tissue will be analyzed in a subgroup of patients.