All X-rays and CT scans use radiation

Dear Dr. Roach: I became short of breath walking upstairs or during mild exercise, like walking a short distance.

My stress test was normal, heart normal and blood pressure good. My doctor has ordered a coronary calcium score.

Should I be concerned about the amount of radiation in this CT scan? — P.M.

A coronary calcium score is performed by a special CT scanner. It determines the amount of calcium in the coronary arteries.

There is a very good but not perfect correlation between calcium in the arteries of the heart and the likelihood of blockages in those arteries. Blockages can cause symptoms, and if they progress or rupture, they can cause a heart attack.

A normal coronary calcium, especially in combination with a normal stress test, makes significant blockages in the artery very unlikely.

All X-rays and CT scans use radiation. However, the amount of radiation from the most modern dedicated coronary calcium CT scanners — called an electronbeam CT — is very small: 0.6 mSv.

This is only a little more than a mammogram.

A different test, the computed tomography angiogram (CTA), can give not only a calcium score, but it also uses dye to look at the inside of blood vessels. It gives information very nearly as good as an angiogram from cardiac catheterization.

However, the radiation dose is much higher — as much as 1,200 mSv: about 200 times as much radiation.

There are still times when the CTA is the better test, but it is costlier in money, a larger radiation dose and dye (which can occasionally damage kidneys).