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HOW FAST IS CORONARY DISEASE PROGRESSING? NEW CT SCORING METHOD GIVES A MORE PRECISE ANSWER

Oak Brook, IL -- A new scoring method to measure the buildup of arterial plaque could give doctors a reliable new tool to monitor the progression of heart disease, according to a study published in the September issue of Radiology.
A noninvasive way of detecting coronary artery disease (CAD) caused by atherosclerosis -- "hardening of the arteries" -- could, if reliable, dispense with the need for coronary angiography in some cases. Angiography, today considered the "gold standard" for diagnosing CAD, is expensive and carries a risk of serious complications. A safer method could be repeated often enough to learn whether the disease is getting worse or better under the influence of one of the promising new medical treatments for CAD.
Patients with atherosclerotic CAD accumulate deposits of fat and hard fibrous tissue, called plaque, that build up in the inner lining of their coronary arteries -- the vessels that supply blood to the heart wall itself. In time the enlarging plaques narrow the arteries and threaten to obstruct them totally. Calcium always is part of the plaque, and it increases in amount as the plaques grow larger and more extensive. Fortunately for radiologists, there is an excellent method for spotting calcium within plaque tissue: electron-beam computed tomography (CT). There is a problem, however, not with the method itself but in how to use the findings to reliably calculate the actual amount of calcium that is present.
Electron-beam CT, using a beam of electrons to create x rays at high speed, is an exquisitely sensitive means of identifying calcified plaque in the coronary arteries. Up to now a traditional calcium score (TCS) has been estimated from the area of plaque in a coronary artery segment and the highest density of calcium in this area. When the TCS increases, there is no way of knowing for certain whether plaque actually has become larger and more extensive, or whether the calcium signal is simply more dense in the same limited area. Also, the slightest change in position can cause a serious error in calculating the TCS.
As reported in the September issue of the monthly scientific journal, Radiology, Tracy Q. Callister, MD, and colleagues, from the EBT Research Foundation and Vanderbilt University in Nashville, Tennessee, appear to have found a better method: the volumetric calcium score, or CVS. This technique "samples" plaque for its calcium content in successive cross-sectional "sections," and uses a well-established calculational technique to reconstruct the plaque 3 dimensionally. The score is not an abstract number like the TCS, but represents the actual volume of plaque calcium. The scoring process makes use of special software and is totally automatic.
When 52 patients with CAD were examined twice only a few minutes apart, differences between the duplicate values were one-third less using the CVS rather than the TCS. The value of any test depends to an important degree on this quality of reproducibility -- the ability to obtain closely similar results when repeating the test. In fact, the CVS proved to be most precise in the very patients who will benefit most from this examination: those with the most extensive plaque. In 27 other patients with substantial coronary disease, CVS estimates repeated after a 12-month interval showed that, overall, CAD had progressed by more than 40%.
The authors claim that the new scoring method makes electron-beam CT a highly reliable method for documenting the progression of coronary atherosclerosis. They believe that when the score increases by 15% or more after a period of follow-up, disease very likely has progressed. Dr. Paolo Raggi, one of the investigators, asserts that "for the first time we can assess with a good degree of reliability the extent of atherosclerotic burden present in the coronary arteries and follow its change over time in a completely noninvasive way."
A cautionary note: electron-beam CT can be used to detect only calcium, not all of the plaque tissue, and therefore does not indicate how severely the coronary arteries are narrowed. Angiography still will be needed in some circumstances, such as when bypass surgery is contemplated.
Radiology is a monthly scientific journal devoted to clinical radiology and allied sciences. The journal is edited by Anthony V. Proto, MD, Medical College of Virginia of Virginia Commonwealth University, Richmond, Va. It is owned and published by the Radiological Society of North America, Inc.

[Coronary artery disease: improved reproducibility of calcium scoring with an electron- beam CT volumetric method, T.Q. Callister et al. Corresponding author: Paolo Raggi, M.D.]