A 74-year-old woman with no significant medical history is admitted with lower gastrointestinal bleeding. The patient undergoes a normal esophagogastroduodenoscopy; colonoscopy reveals diverticulosis and blood throughout the colon with no site of active bleeding or adherent clot. Two days later, the patient develops recurrent hematochezia with transient hypotension that responds to transfusion. A technetium 99m–tagged red blood cell scan demonstrates active bleeding in the right colon. The best next step in management is: