China’s Covid-19 pandemic lockdowns have led to a shortage of a dye widely used in medical scans, prompting U.S. hospitals including the Mayo Clinic to ration supplies, postpone procedures or switch to less optimal imaging. The shortage arose in recent weeks for iodinated contrast media products including Omnipaque, made by General Electric Co.’s GE Healthcare unit at a plant in Shanghai. Omnipaque is given by intravenous injection to patients before imaging procedures to make internal organs, blood and vessels more visible in procedures such as CT scans.