Some hospitals in the St. Louis area could be unnecessarily exposing patients to radiation by giving them more CT scans than they need, according to data released Wednesday.

The information is part of the Centers for Medicare & Medicaid Services hospital comparison system that releases new data on patient satisfaction and quality measures.

At least 12 hospitals in the area perform abdominal CT (computed tomography) scans at high rates, the data show. The scans produce images of the body using radiation that can be harmful and pose a risk of cancer.

Some hospitals may be "routinely giving patients combination CT scans of the abdomen when a single scan is all they need," according to the Medicare guidelines.

A single abdominal CT scan exposes a patient to 11 times the radiation of a regular X-ray. Of all abdominal scans performed on Medicare patients in the U.S., 19 percent are performed as a combination of two scans.

At SSM St. Clare Health Center in Fenton (formerly St. Joseph Hospital of Kirkwood), 73 percent of abdominal scans are doubled, according to the report. SSM St. Mary's Health Center in Richmond Heights performs combination scans 68 percent of the time. At 67 percent, St. Anthony's Medical Center in south St. Louis County has the third-highest rate in the area.

Touchette Regional Hospital in Centreville has the lowest rate with 0 percent.

The CT scan data were based on 2008 figures. A spokeswoman for SSM Health Care said the company has since implemented a policy to reduce the number of combination scans for emergency room patients.

"Our goal here is not to label hospitals as good or bad but to provide insight to the hospitals as well as to the general public ... to achieve universally safe, effective care," said Dr. Barry Straube, chief medical officer for Medicare, in a conference call with reporters.

The new data also show which hospitals perform unnecessary MRI (magnetic resonance imaging) tests on patients complaining of lower back pain. In most cases, the pain resolves on its own and does not require an MRI for diagnosis, according to Medicare guidelines.

The scans can be expensive and stressful but do not expose the patient to radiation.

In its data, Medicare looked at the percentage of patients with back pain who probably did not need an MRI but got one before trying other treatments. The national average is 33 percent.

The five local hospitals with the highest percentage of MRIs were:

• St. Mary's, 40.4

• Des Peres Hospital, 39.6

• Christian Northeast Hospital, 39.1

• St. John's Mercy Medical Center, Creve Coeur, 37

• SSM St. Joseph Health Center, St. Charles, 37

The five with the lowest percentage:

• Gateway Regional Medical Center, Granite City, 24.5

• Barnes-Jewish West County Hospital, 29

• Barnes-Jewish Hospital, Central West End, 30

• Anderson Hospital, Maryville, 30.9

• St. Luke's Hospital, Chesterfield, 31

To view the hospital data, visit www.hospitalcompare.hhs.gov/