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Questions in Cardiovascular CT
How much calcium is too much calcium for coronarycomputerized tomographic angiography?
Harvey S. Hecht, MD, FACC*, Tandeep Bhatti, DO
Lenox Hill Heart and Vascular Institute, 130 E 77th Street, New York, NY 10021 USA
Abstract. The coronary artery calcium (CAC) score above which it is recommended that coronary
computerized tomographic angiography (CTA) not be performed has been steadily increasing. Cur-
rently, calcium scoresϾ 1000 are thought to prohibit CTA accurate interpretation. However, a reasoned
approach suggests that there is no absolute upper limit that applies to all patients and imaging centers.
To anticipate the problems posed by calcium, a CAC scan must be obtained before CTA. Understanding
the clinical goals of the CTA and the source and recognition of CAC-based imaging artifacts can enable
accurate clinical CTA examinations even in the setting of high calcium scores.
© 2008 Society of Cardiovascular Computed Tomography. All rights reserved.
KEYWORDS:Artifacts;
Coronary calcium;
CTA
Introduction
The coronary artery calcium (CAC) score above which itis recommended that coronary computerized tomographic
angiography (CTA) not be performed has been steadily
increasing. Currently, calcium scoresϾ 1000 are thought to
prohibit CTA accurate interpretation. However, a reasoned
approach suggests that there is no absolute upper limit that
applies to all patients and imaging centers.
To anticipate the problems posed by calcium, a CAC
scan must be obtained before CTA. Most centers perform
CAC scanning before CTA; many do so only on request.
Although routine CAC scanning is advisable, for centers in
which is not the clinical routine, heavy calcification will be
apparent on the scout chest scan performed before contrastinjection and should alert personnel to the potential prob-
lem.
General considerations
CTA objectives
There are 2 broad goals of CTA. The first goal is detection
of obstructive disease. The quantitative approach to stenosis
measurement depends on the ability to clearly separate contrast
from calcified plaque, whether lesion severity is determined
from qualitatively “eyeballing,” or a quantitative measurement,
or from cross-sectional analysis and derivation of minimum
luminal area. However, it is critical to realize that a clinically
effective CTA scan result does not require the ability to accu-
rately analyze every millimeter of the vessel. Rather, the cru-
cial issue is to arrive at the appropriate clinical recommenda-
tion. Consequently, if in most cases there is readily detectiblesignificant obstructive disease secondary to evaluable, less-
calcified plaque, the inability to evaluate heavily calcified areas
is rendered irrelevant. For example, in Figure 1, an 88-year-old
man with a CAC score of 4253 underwent CTA. There was
clearly significant left main and right coronary stenosis sec-
ondary to almost entirely noncalcified plaque, in addition to a
significant left anterior descending stenosis resulting from
mixed plaque. The presence of adjacent densely calcified non-
evaluable areas did not interfere with arriving at the correct
diagnosis.
Conflict of interest: Dr. Hecht discloses that he received grant support
and honoraria from Philips Medical Systems. Dr. Bhatti reports no conflicts
of interest.
* Corresponding author.
E-mail address: [email protected]
The online version of this article contains supplementary data.
Submitted April 9, 2008. Accepted for publication April 16, 2008.
1934-5925/$ -see front matter © 2008 Society of Cardiovascular Computed Tomography. All rights reserved.
doi:10.1016/j.jcct.2008.04.003
Journal of Cardiovascular Computed Tomography (2008) 2, 183–187
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In addition, data suggest that the more severe stenoses are
associated with less-calcified plaques, minimizing the impor-
tance of the densely calcified areas.1 The increased positive
remodeling associated with extensively calcified plaque pre-
serves the lumen, despite the large plaque burden. Nonetheless,
there will be cases with extensive calcified plaque that will
prevent evaluation of those sites, without clear obstructive
disease elsewhere. In these situations, it is appropriate to state
in the report that “There is extensive calcified plaque at whichlocation significant stenosis cannot be excluded”.
The second goal is assessment of plaque burden. Char-
acterization and quantitation of both noncalcified and cal-
cified plaque offers a more complete assessment of risk than
does the calcified component alone. In general, the degree
of vulnerability is thought to be directly related to the
noncalcified component. A quantitative assessment of
calcified plaque and a semiquantitative evaluation of non-
calcified plaque enable stratification of the extent of ath-
erosclerosis, which in some centers is considered of equalor greater importance than evaluation of obstructive dis-
Figure 1 An 88-year-old man presented with chest pain. The CAC score was 4253 with extensive calcified plaque in all vessels. CTA
showed readily apparent, significant left main (LM) (A) and right coronary artery (RCA) (C) stenoses associated with almost exclusivelynoncalcified plaque, as well as significant left anterior descending (LAD) coronary artery lesions secondary to mixed calcified and
noncalcified plaque. The findings were confirmed by invasive angiography (B and D).
184 Journal of Cardiovascular Computed Tomography, Vol 2, No 3, May/June 2008
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ease. Clearly, this analysis is not hindered by calcified
plaque.
Calcium artifacts
Technical problems are inherent in CT imaging regionsadjacent to calcified plaque of varying densities.
Partial volume effect
Calcific densities may create artifacts because densities
are greatly influenced by the “company they keep.” En-
hancement of the Hounsfield units of adjacent contrast by
the partial volume effect of the denser calcium (blooming)
may make the calcified region appear larger and thus over-estimate the degree of luminal obstruction. Broadening the
Figure 2 A 64-year-old woman underwent coronary CTA for evaluation of chest pain. CAC score was 1962. CTA of the left main and
left anterior descending (LAD) arteries showed extensive calcified plaque. Increasing the window width from 806 HU (A) to 3970 HU(B) dramatically decreased the apparent size of the calcified plaques. Analysis of cross-sectional images obtained from the straightened
multiplanar reconstruction (D) showed no change in Hounsfield units (E and F) despite the dramatic reduction in size and appearance of
the calcified plaque. Invasive angiography showed no significant disease (C).
185Hecht and Bhatti How much is too much calcium for CTA?
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gray scale by increasing the width of the image windowmay visually shrink the size of the calcified plaque and
appear to make it less space occupying. However, this is
merely an optical illusion; the Hounsfield units do not
change (Fig. 2), and this technique should be used cau-
tiously. After window widening to evaluate a large calcified
plaque that appears to occupy the entire lumen, the least
dense area may still be calcium and should not be mistak-
enly identified as contrast. The use of a sharper reconstruc-
tion filter, as would be used for stent analysis, may decrease
the blooming and facilitate interpretation of highly calcified
segments.
Shadowing
If the calcium density is very high, eg, Ͼ1000
Hounsfield units (HUs), the contrast may appear hypodense
as the result of photopenia from the “shadowing” effect of
the calcium, even in the absence of any significant stenosis.
Unfortunately, there is no absolute level of calcium
Hounsfield units above which there will be shadowing and
below which there will be a partial volume effect. In gen-
eral, the greater the Hounsfield unit gradient between the
calcified plaque and the adjacent hypodense area, the more
likely is the contribution of shadowing to the hypodensity.The CTA of the left circumflex in a 65-year-old man with a
totally occluded left anterior descending coronary artery isshown in Figure 3. The apparent severe ostial stenosis
secondary to mixed plaque was, in reality, the result of
shadowing of the lumen by the dense calcification, mimick-
ing the appearance of a critical lesion.
Motion
Motion artifacts, whether secondary to rapid heart rate,
arrhythmias, patient motion, or respiration, are exaggerated
in calcified compared with noncalcified areas. Conse-
quently, the use of -blockers for heart rate reduction to
Ͻ60 beats/min is recommended to minimize image blur-ring.
Patterns of calcification
Equally high calcium scores may result from numerous
small nonobstructive plaques that will not interfere with
image interpretation, or from several large calcified plaques
that make interpretation difficult. In reality, even a CAC
score of 100 may pose a problem if there is a single dense
plaque. In Figure 4, a single moderately large calcified
plaque obscures the lumen (Fig. 4A) in an angiographically
minimally narrowed vessel (Fig. 4B), whereas multiplesmaller calcified plaques do not obscure 3 significant focal
Figure 3 CTA of the left circumflex (LCx) coronary artery in a 65-year-old man with a totally occluded left anterior descending coronary
artery showed a severe ostial stenosis secondary to mixed calcified and noncalcified plaque (A). Subsequent invasive angiography
(B) showed no obstructive disease. The apparent narrowing was the result of shadowing of the lumen by the dense calcification, mimicking
the appearance of a critical lesion.
186 Journal of Cardiovascular Computed Tomography, Vol 2, No 3, May/June 2008
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stenoses (Fig. 4C), confirmed on invasive angiography
(Fig. 4D).
Recommendations
In summary, there can be no arbitrary, absolute calcium
score above which coronary CTA should not be performed.
Rather, each case must be individualized with respect to the
primary purpose of the examination (evaluation of obstruc-
tive disease versus plaque burden), the pattern of calcifica-
tion, and the expertise of the interpreting physician. A CAC
score Ͼ1000 or a pattern of isolated large, dense calcifica-
tions even with CAC Ͻ1000 should alert personnel to
potential interpretation problems and should not be fol-
lowed by CTA if the interpreting physician does not have
extensive experience in dealing with these issues.
After increasing experience, at a point to be determinedby the comfort level of each practitioner preferably with the
guidance of a mentor, physicians may authorize the perfor-
mance of CTA in patients with these CAC characteristics, to
be analyzed with full understanding of the principles de-
scribed above. There is no absolute minimum number of
cases to acquire the requisite expertise.
Reference
1. Lubarsky L, Prakash M, Jelnin V, Panogopoulos G, Hecht HS: Relation
of plaque composition to degree of stenosis evaluation by 64 detectorCTA. J Cardiac Computed Tomogr. 2007;1(suppl):S34.
Figure 4 A patient with a CAC score of 135 in which a single moderately large calcified plaque in the left anterior descending (LAD)
coronary artery obscures the lumen (A) and poses interpretive problems in an angiographically minimally narrowed vessel ( B). In sharp
contrast, in a patient with a CAC score of 2341, multiple smaller calcified plaques in the left anterior descending coronary artery do not
obscure 3 significant focal stenoses (C), confirmed on invasive angiography (D).
187Hecht and Bhatti How much is too much calcium for CTA?