President Obama has pledged that a revamped healthcare system would hold down exploding costs. But efforts to control medical practices that have driven up expenses, including physician "self-referrals," underscore how difficult it is to alter entrenched patterns. A host of studies and reports by academics and the federal government shows that physicians who own scanners order many more scans than those who do not. As a result, Americans pay billions of dollars in extra taxes and insurance premiums.