NEW YORK (Reuters Health) - Scans of people's knees are less likely to reveal a problem when the referring doctor has a financial stake in the imaging center or the equipment used, suggesting some tests may be unnecessary, according to a new study. When doctors have a financial interest in the imaging facility, their patients are 33 percent more likely to get a test result that shows nothing wrong, compared to patients of doctors with no financial interest, U.S. researchers found. "It does raise the questions: Are these studies being performed unnecessarily? Are these machines being over utilized because of an unconscious bias?" Dr. Matthew Lungren, the study's lead author said.