Most American laboratories are exposing patients to excess radiation when they undergo a commonly performed heart test, a new study reports.

Myocardial perfusion imaging is a non-invasive test that uses a special radioactive tracer known as thallium to compare the function of the heart and the flow of blood at rest compared to during exercise. The test is performed for many reasons, including to diagnose coronary heart disease and develop a treatment plan.

But a new study shows that only 14 percent of U.S. facilities met the quality benchmark of exposing patients to no more than the amount of radiation recommended by the procedure guidelines, as compared with 32.6 percent of facilities in 64 other countries, according to a report in MedPage Today.

The dose of radiation performed in the U.S. labs was 20 percent higher on average than in the other countries, according to the team, which was lead by researchers from Columbia University Medical Center/New York-Presbyterian Hospital in New York City.

The study also showed that very few (7.7 percent) of the U.S. labs employed the  “stress-only” protocol compared to nearly 85 percent of the European labs.   In this procedure, only the first imaging test is taken of the heart at rest, and the second part omitted if the results are normal.

This manner of performing the test has been found to reduce radiation by more than 60 percent, according to the study, which appears online in JAMA Internal Medicine.