Nearly half of patients receiving medical imaging for clinical trials get an added surprise - the discovery of a tumor or infection unrelated to the study but potentially important for their health.

According to a paper published Monday in the Archives of Internal Medicine, radiologists detect an incidental finding in around 40 percent of patients undergoing medical imaging for research.

The researchers, led by Dr. Nicholas Orme, of the Mayo Clinic in Rochester, Minn., evaluated medical records of 1,426 patients who underwent an imaging procedure as part of a 2004 study. Each image was interpreted by a radiologist the day it was performed, and an expert panel reviewed all IFs that resulted in a clinical action during a three-year follow-up period.

Image exams included those from CT, MRI, ultrasound, X-ray and nuclear medicine.

Of the research imaging exams, an IF occurred in 567 - 39.8 percent - of them. The researchers reported that the risk of an IF increased with age. Further, more IFs were found in patients undergoing computed tomography scans of the abdomen and pelvic area than any other procedure, followed by CT scans of the chest and magnetic resonance imaging of the head.

In 6.2 percent of IF cases, clinical action was taken. But in most of those cases - 4.6 percent of all IF cases - the medical benefit or burden of these actions were unclear, the researchers reported. However, action resulted in "clear medical benefit" for 1.1 percent of patients and a "clear medical burden" in 0.5 percent.

The findings, Orme told DOTmed News, aren't completely surprising - in retrospect, they make sense, he said.

"It makes sense that a CT of the abdomen and a CT of the pelvis [would show more IFs] because they give a lot of detail about a patient's anatomy," he said.

What was surprising, Orme said, was how in most cases, it was hard to see whether there was a harm or benefit in investigating IFs. Orme predicted there would be a larger swing toward benefits.

In some cases, detection of something that warranted further attention wouldn't necessarily have happened without patients undergoing research imaging exams, said Orme.

"It's difficult to say across the board," he said. "In some instances, they probably would have been found and our research studies maybe gave lead time. However, I think there are a couple examples where I don't think that an incidental finding would have been picked up as early [if not through the research]."

In an accompanying editorial, Dr. Bernard Lo of the University of California, San Francisco pointed out that ethical concerns may arise when a researcher learns information about a patient that is not relevant to the research but may have "important clinical implications" for that patient.

"Although [IFs] may offer the possibility of substantial personal benefit to the participant, more commonly they are false-positive findings that lead to a cascade of testing that presents additional risks and burdens," Lo wrote.

He suggests that researchers develop a plan before going into the study for how they will deal with IFs, including what findings they will share with patients.

For the Mayo Clinic, explained Orme, even for research purposes, a radiologist will look at a patient's exam the same day to determine if any IFs are present. If something is worrisome, that information is relayed to the patient's physician who will then determine the best route to take.

"In imaging research as a whole throughout the country, that isn't always the case," he said. "In some instances, [the image] may be read by a radiologist months and months down the line. Theoretically, you could lose a window to intervene."

The implications of these findings, said Orme, are knowing how common IFs are and how researchers can predict, to some degree, the level of IFs found, based on the type of imaging modality used and the age group.

"If you're looking at a femur [X-ray], it may not have many incidental findings...But with a CT of the abdomen for an older patient, you should realize there may be a lot of incidental findings, and you have to have a mechanism...to deal with those."