You may have heard about heart scans, a kind of imaging to determine your risk of heart disease.

A new study from the Journal of the American Medical Association shows how quickly this technology is evolving.

The scans can be helpful, because if the arteries that carry blood to your heart become blocked, it increases the risk of heart attack. There are a few ways to look for blockages.

"We typically do angiography, meaning we put catheters into the arteries and then inject dye to see if we can see different parts of the artery wall," said Samir Kapadia of the Cleveland Clinic.

But scans are not invasive and are more comfortable for the patient.

"In this study we actually analyzed the accuracy of the first generation of cardiac CT for the detection of blockage in the coronary arteries," said Dr. Mario Garcia.

Researchers at the Cleveland Clinic Foundation studied the first-generation cardiac CT machine, which captures 16 images of the heart and arteries per rotation of the machine.

The researchers compared scans and angiograms for almost 200 patients.

They found that a negative result can be trusted to be accurate, but a positive result leaves the diagnosis in doubt.

In other words, if the CT test says you don't have a blockage, believe it, but if it says you do, you can't be so sure it's right.

Many centers now use the new generation of scanner that has 64 detectors, and is more accurate than the first generation, which is only a few years old, the report said.