Since the early days of cardiac pathology in the late nineteenth century, doctors have known that calcium is deposited in the plaques of atherosclerosis, as it is anywhere in the body where inflammation occurs. Calcium puts the hardness in “hardening of the arteries.”

So it seems logical that a test for calcium in the arteries would help diagnose heart disease. Until recently, we didn’t have the technology to detect early buildups of calcium. After all, the coronary arteries are small, just 2 to 4 mm in diameter, and take many twists and turns as they travel around the heart muscle.

And they are in constant motion, gyrating with each heartbeat. Think of trying to take a picture of a strand of spaghetti as it shimmies in boiling water, and you’ll have some idea of what scientists face when they try to obtain images of the coronary arteries.

It’s a daunting task, but it is exactly what electron beam computed tomography (EBCT, also called ultrafast CT) has accomplished. EBCT uses an electronically steered electron beam to produce x-rays. The beam can rotate around the patient much faster than an x-ray generator can, so EBCT is faster than other CTs—fast enough to take a picture of a beating heart.

EBCT obtains each image in just 1⁄20 of a second, about twenty times faster than a helical CT. EBCT generates a calcium score that provides a very accurate measurement of the amount of calcium in a person’s coronary arteries. The more calcium, the higher the score—and the more atherosclerosis.

But does the calcium score predict actual cardiac events? It does. Many studies have been completed to date, and most agree that people with the highest scores have the highest risk. A 2003 Illinois study of 8,855 people between the ages of thirty and seventy-six is a good example.

None of the subjects had been diagnosed with coronary artery disease before their EBCTs. Each person provided information about his or her health and cardiac risk factors. The researchers tried to contact each subject after an average of thirty-seven months; they were able to reach 4,155 men and 1,484 women.

Although the men were younger (average age fifty) than the women (average age fifty-four), the men had higher average calcium scores (137 vs. 59).

Even after taking standard cardiac risk factors into account, the 25 percent of men with the highest scores were four times more likely to suffer a heart attack or die from heart disease than the 25 percent of men with the lowest scores; they were also twenty-six times more likely to need bypass operations or angioplasties.

But although the calcium score did predict the need for surgery or angioplasty in women, it did not predict heart attacks or cardiac events. This study is one of the most impressive demonstrations of the power of EBCT, but it has flaws. All the subjects referred themselves for scanning, so they may have had symptoms or other reasons to worry about their hearts.

The scientists did not measure the cardiac risk factors themselves but relied on the subjects’ own reports. Finally, the researchers were unable to contact more than a third of the original group. All these limitations make it hard to say that the results apply to the whole population of adults without cardiac symptoms.

Still, experts agree that EBCT can detect coronary artery calcium and that high scores tend to indicate risk. However, an obvious weakness of EBCT is its inability to detect plaques that lack calcium (which includes many small plaques, the ones most likely to rupture and trigger heart attacks).

So should you run out and get an EBCT scan? Probably not, especially if you have a high or low risk for heart attack. The test is not likely to help low-risk individuals who would probably have low scores and are likely to stay healthy in any case. At the other extreme, high-risk individuals should receive treatment regardless of their calcium scores, so an EBCT is unlikely to help them.

If your level of risk is in the middle, there might be a value in determining your calcium score to assess how aggressively to treat you, but as of now, it’s unproved how valuable it would be. Plus, insurance companies most likely would not cover it.

Like other hightech diagnostic tests, EBCTs are now being marketed directly to the public. For a fee, you can bypass your doctor and buy yourself a scan. But should you? No. You and your doctor should work together to decide whether the test makes sense. Otherwise, you may just be wasting your money.

More research is needed to learn whether a high calcium score adds significantly to the information provided by much less expensive, better-studied risk indicators. And even if calcium scores add significantly to the risk profile, scientists will have to determine if this information leads to effective treatments and a better outcome.

The large government Multi-Ethnic Study of Atherosclerosis is already under way, but it’s not expected to answer these questions until around 2010. EBCT is an example of a recurring dilemma in modern medicine: technology has arrived before doctors have learned how best to use it.