What is the role of helical CT in the imaging workup of cardiac calcification?

Updated: Sep 10, 2019
  • Author: Sohail G Contractor, MD, MBBS; Chief Editor: Eugene C Lin, MD  more...
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Answer

Scans are performed with acquisition times approaching 0.5 second to 250 milliseconds; the faster acquisition is possible with the newer multidetector scanners. Calcific deposits are identified as bright white areas along the course of coronary arteries (see the image below). [49, 50, 51, 52]

Helical non–contrast-enhanced CT reveals calcifica Helical non–contrast-enhanced CT reveals calcification involving the left main coronary artery.

Coronary calcifications detected on EBCT or helical CT can be quantified, and a total calcification score can be calculated. In this schematic, an arbitrary pixel threshold of +130 Hounsfield units (HU) (+90 for some helical scanners) covering an area greater than 1 mm is often used to detect coronary artery lesions. Regions of interest are placed around the area of calcification. Once the region of interest is placed, scanner software displays peak calcification, attenuation in HU, and area of the calcified region in millimeters squared. The volume or Agatson score is displayed. The volume score is the area of the lesion, while the Agatson score is weighted to consider attenuation of pixels, as well as the area.

In the Agatson scoring system, +130-200 HU lesions are multiplied by a factor of 1, +201-300 HU by a factor of 2, +301-400 HU lesions by a factor of 3, and lesions greater than 401 HU by a factor of 4. The sum of the individual lesion scores equals the score for that artery, and the sum of all lesion scores equals the total calcification score.

In one study, a total calcification score of 300 had a sensitivity of 74% and a specificity of 81% in detecting obstructive CAD. The negative predictive value of a zero calcification score was 98%. In another study, sensitivity for detecting calcific deposits in patients with angiographically significant stenosis was 100%, and specificity was 47%. In the same study, 8 patients without calcification showed no angiographic evidence of CAD, while 28 patients with calcification showed mild or moderate CAD.

However, despite the high sensitivity of EBCT, calcification scores do not always predict significant stenosis at the site of calcification. [53, 54] In another study, EBCT was compared with coronary angiography; only 1 patient with stenosis greater than 50% on angiography did not demonstrate coronary calcification on EBCT. Thus, absence of calcification appears to be a good predictor of the absence of significant luminal stenosis. However, absence of calcification does not always indicate the absence of atherosclerotic plaque.

A multicenter study reviewed cardiac event data in 501 mostly symptomatic patients with CAD who underwent both EBCT and coronary angiography. In this group, 1.8% of patients died and 1.2% had nonfatal myocardial infarctions during a mean follow-up period of 31 months. A calcification score of 100 or more was revealed to be highly predictive in separating patients with from those without cardiac events.


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