Using radioactive tracers and drugs that trigger the arteries to dilate, nuclear scanning will be able to track blood flow throughout the heart muscle mass, in a test referred to as myocardial perfusion imaging .The RegEx trial is comparing an investigational vasodilator drug, regadenoson, against a commercially available alternative, adenosine. Regadenoson can be both simpler to administer than adenosine and even more geared to the arteries of the heart, a feature that is expected to minimize side effects.The purchases violated a 2005 ban on covering the drugs beneath the U.S. Health program for the elderly and disabled. Medicare administrators blamed the spending on a software error and said they might try to recover payments to private insurers who administer the program's drug plans. Medicare ‘shouldn’t have covered these drugs,’ George Reeb, acting deputy inspector general for audit solutions at the U.S. Department of Human and Health Services, wrote in a written report released today. He recommended that Medicare use the Drug and Meals Administration to maintain a listing of prohibited drugs.