CHICAGO (AP) — There may be good reason to ask about financial ties if your doctor orders an expensive imaging test for your aching back: Patients whose physicians own the equipment are more likely to get scans they might not need than those whose doctors have no financial interest, a small study suggests.

Researchers analyzed reports on 500 MRI scans performed on patients with lower back pain that had been sent for review to Duke University. Of the scans with normal results, 106 were ordered by orthopedic surgeons who owned the machines versus 57 by doctors without financial ties.

The normal scans accounted for about half of those ordered by surgeons with financial connections, compared with about a quarter in the other group. The authors only examined the scans, so there's no information on the patients' medical history or outcome.