Click here to get general information about CT scans from the National Institutes of Health.

Click here to link to an abstract (a brief summary) of research that Dr. Aaron Sodickson presented last year at the annual meeting of the Radiological Society of North America, held in Chicago.

Cardiac CT scans

Doctors are weighing the pluses and minuses of using CT scans to detect heart disease and, more specifically, coronary artery disease — the atherosclerotic blockages in the arteries that supply the heart that can lead to heart attacks.

A standard chest x-ray will show an outline of the heart and some larger blood vessels, but smaller structures and vessels don’t show up.

An angiogram is any x-ray picture of the coronary arteries. The traditional coronary angiogram, which was introduced in the 1960s, does an excellent job of showing small blood vessels, and it has become an essential diagnostic tool in contemporary cardiology.

But it’s a pretty invasive procedure that involves snaking a slender catheter from the femoral artery in the groin up into the coronary arteries, where a dye is released. That dye, or contrast agent, is necessary to make the fine details of the blood vessels show up on the x-ray.

CT scanning of the coronary arteries — the formal name is cardiac CT angiography — still involves injection of a contrast agent, but there’s no threading of a catheter through the vascular system. So, relative to traditional angiogram, it’s far less invasive. And in most circumstances, cardiac CT scanning is less expensive and much faster than the traditional angiogram.

Speed is one reason emergency department doctors are interested in using CT scanning to diagnose people with chest pain. Several studies have shown that it might be a good way to quickly rule out whether someone is having a heart attack. But there’s a lot of debate about cardiac CT scanning, particularly when it comes to the nonemergency cases.

One question is whether it’s as accurate as traditional angiography. A study published in New England Journal of Medicine in 2008 suggested that it is getting close: the authors concluded that CT scanning “has a reliable accuracy for the diagnosis of obstructive coronary disease,” and that it’s similar to conventional angiograms in its ability to identify patients who need revascularization (usually angioplasty).

But they added that CT scanning can’t replace conventional angiograms because it’s just not quite as accurate by some measures (positive and negative predicative values).

Another major question with cardiac CT scanning is radiation exposure and whether doctors are adopting a test that will increase cancer risk.

There’s no question that cardiac CT scanning can result in a considerable amount of radiation. The biologically effective dose from a chest x-ray is 0.02 millisieverts (mSv). According to a study published in the Journal of the American Medical Association (JAMA), the median dose from cardiac CT scan is 600 times that amount, or 12 mSv. And that’s more than double the 5 mSv exposure from the traditional invasive angiogram.

The good news from the JAMA study was that adjustments to how scans are done, as well as improvements to the CT scanners themselves, can lower the radiation dose quite a bit. The authors point to small studies in which the exposure is 2.1 mSv.

At the 2008 Radiological Society of North America meeting in Chicago, researchers presented preliminary findings from an industry-sponsored study showing that an ultrafast CT scanner (320-slice vs. the standard 64-slice machine) could reduce the radiation exposure from a cardiac CT scan down o 4.65 mSv.