Getty Images A patient in end-stage kidney disease receives dialysis while he waits for a kidney transplant. Researchers at Washington University School of Medicine in St. Louis have developed an imaging agent that could help refine assessments of kidney health, potentially salvaging some otherwise discarded kidneys. More than 3,000 donated kidneys are discarded every year in the U.S., even as thousands of people die on kidney transplant waitlists. About a fifth of all donated kidneys — particularly those from people who are older, have metabolic or cardiovascular conditions, or have died — are deemed poor quality. Doctors and patients often refuse such kidneys rather than risk transplanting an organ that might not work.