BAKERSFIELD, Calif. -- When a patient comes to the hospital with a heart attack, doctors often perform multiple imaging tests to locate blocked arteries and determine the amount of heart damage.

Each test generally exposes the patient to a moderate amount of radiation, but when combined, the scans pack quite a punch.

In a new study, researchers from Duke University analyzed information on more than 64,000 heart attack patients at 49 U.S. hospitals.

They found that patients received an average of seven tests that use radiation, including X-rays, certain catheter procedures, and CT scans.

Together these tests equaled the amount of radiation in 725 X-rays -- close to one-third the amount permitted for nuclear plant workers over the course of a year.

Researchers said the fact that patients are receiving such a high dose of radiation in one hospital stay is concerning.

They did not recommend eliminating any one test, but they suggest doctors think hard before ordering more scans to be sure that each one is absolutely necessary.