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Multi-slice fast CT and Electron Beam Tomography
the first screening step in imaging coronary
atherosclerosis? Stephan Achenbach,
MD Department of Cardiology, University of
Erlangen, Germany
2
Abstract
Coronary artery disease events such as myocardial
infarction or coronary death frequently occur in
previously healthy individuals without prior
symptoms. Tests which permit identification of
individuals at increased risk may thereore be
beneficial. Since coronary events are in most
cases caused by plaque rupture, imaging methods
which permit the identification and
quantification of coronary atherosclerotic plaque
are potentially useful for risk stratification.
Most non-invasive imaging techniques, however,
lack the combination of high temporal and spatial
resolution which is necessary to reliably
visualize the coronary arteries. Electron beam
tomography (EBT) and, more recently, multi-slice
spiral CT have been shown to permit visualization
and quantification of coronary calcium in a
non-invasive fashion. Coronary calcium is always
caused by coronary atherosclerosis and the amount
of coronary calcification correlates to the
overall atherosclerotic plaque burden. Numerous
clinical studies conducted by electron beam
tomography have proven the methods potential to
identify individuals at increased risk for
coronary events through detection and
quantification of coronary calcifications. Most
(but not all) studies have demonstrated a higher
predictive value of coronary calcifications as
compared to traditional risk factors. Even though
some smaller studies have shown that mulit-slice
CT (MSCT) in conjunction with ECG-gated
reconstruction techniques permits the detection
and quantification of coronary calcium with
accuracies similar to electron beam tomography,
no clinical outcome data have so far been
published using MSCT. In conclusion, the
detection and quantification of coronary
calcification my be a useful tool for the
identification of individuals at increased risk
for coronary events.
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Introduction
Coronary events - such as myocardial infarction -
are usually caused by plaque rupture and
frequently occur in previously asymptomatic
individuals
4
Introduction
Traditional risk factors frequently do not permit
satisfactory identification of individuals who
are at increased risk for coronary artery events
5
Introduction
Imaging techniques for the non-invasive
detection of atherosclerotic plaque in the
coronary arteries may be helpful to identify
individuals at increased coronary event
risk. However, both high temporal and high
spatial resolution are necessary to visualize the
corornary arteries in a non-invasive fashion.
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Introduction
Electron beam tomography is a cross-sectional
x-ray imaging technique with a temporal
resolution of 100 ms.
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Introduction
Electron beam tomography permits the sensitive
detection and quantification of coronary artery
calcification.
Calcium in LAD LCX
Calcium in RCA
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Introduction
Aquisition protocols and methods for
quantification of coronary calcium by EBT are
standardized and large reference data bases are
available1, 2.
Severe calcification in LAD
Abscence of coronary calcium
9
Introduction
Recent pre-clinical work has shown that
multi-slice spiral CT using the last hardware
generation and sophisticated ECG-correlated image
reconstruction software also permits coronary
calcium detection 4,5.
LAD calcifications in retrospectively ECG-gated
multislice CT
10
Introduction
However, care has to be taken in order to avoid
motion artifacts which may be more frequent due
to the longer acquisition window as compared to
EBT
Same patient prospectively triggered (left) and
retrosplectively triggered MSCT
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Discussion
What is the rationale behind the detection of
coronary artery calcification?
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Discussion
Why detect coronary calcium?
Coronary calcification is always caused by
artherosclerosis 6
13
Discussion
Why detect coronary calcium?
The amount of calcium correlates to overall
plaque burden 7,8
However no close relationship between calcium in
a vessel segment and degree of luminal stenosis.
14
Discussion
Even though calcium does not permit to
specifically detect vulnerable plaque, it is
wrong to assume that calcified plaques are stable
or more frequently stable than non-calcified
plaques9.
Presence of Calcium
acute rupture
stable
healed rupture
erosion
vulnerable
15
Discussion
Coronary calcium does not permit to detect the
vulnerable plaque, but it permits to detect the
patient with high coronary atherosclerotic plaque
burden in an asymptomatic stage.
16
Discussion
A number of clinical trials have evaluated the
predictive value of coronary calcium detection by
electron beam tomography in symptomatic and
asymptomatic individuals.
17
Discussion
Raggi et al10
632 asymptomatic patients 32 /- 7 months
follow-up myocardial infarction and death Annual
event rate 0.1 for calcium score of 0 2.1
for calcium score 1-99 4.1 for calcium score
100-400 4.8 for calcium score gt 400 70 of
events in 25 of patients with highest calcium
score Raggi et al, Circulation 2000
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Discussion
Arad et al11
1173 asymptomatic patients 1 year and 3.5 year
follow-up Risk ratio for coronary events 23
for calcium score gt 160
19
Discussion
Meta analysis by OMalley et al12
Calcium score above median All events
RR 8.6 Hard events RR 4.2
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Discussion
In most studies, coronary calcium by EBT was more
predictive than conventional risk Arad et al
1996 ROC 0.91 for calcium, 0.74 for RF 1173
asymptomatic subjects (mean age 53 years) Raggi
et al 2000 OR 22 for calcium, 7.0 for RF 632
asymptomatic subjects (mean age 52
years) Detrano et al 1999 ROC 0.65 for calcium,
0.67 for RF 1196 asymptomatic high-risk subjctes
(mean age 67 years)
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Discussion
Keelan et al13
288 patients with CAD who underwent coronary
angiography. Follow-up 6.9 years. Event-free
survival was significantly higher for patients
with calcium score lt 100 than for those with
scores gt 100.
22
Discussion
In summary, a number of studies have proven the
prognostic value of coronary calcium detection by
electron beam tomography in asymptomatic and
symptomatic populations. Study results are not
completely unanimous concerning the superiority
of coronary calcium over traditional risk
factors, but most studies found coronary calcium
to have a higher predictive value. No clinical
outcome studies have so far been performed using
multi-slice CT.
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Discussion
What is the potential clinical role of coronary
calcium detection? AHA/ACC statement14
A positive EBCT confirms the presence of
coronary atherosclerotic plaque. Total amount
of calcium correlates ... total amount of
atherosclerotic plaque. A negative EBCT test
makes the presence of atherosclerotic plaque,
including unstable plaque, very unlikely. A
high calcium score may be consistent with a
moderate to high cardiovascular event risk within
2-5 years. A negative test ... low risk of a
cardiovascular event in the next 2 to 5 years.
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Discussion
What is the potential clinical role of coronary
calcium detection? In clinical practice, cleary
low-risk and clearly high-risk individuals
probably do not need further testing for risk
stratification. Intermediate risk patients,
however, might profit
ACC/AHA14 selected use of coronary calcium
scores when a physician is faced with the patient
with intermediate coronary artery disease risk
may be appropriate
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Discussion
What is the potential clinical role of coronary
calcium detection?
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Conclusion
Role of EBT and MSCT in risk stratification? Coro
nary calcium, even though it does not permit to
detect the vulnerable plaque, permits to
identify the patient with high plaque burden.
The detection of coronary calcium therefore
permits identification of patients at increased
risk for coronary artery events. It may be
beneficially applied in patients who seem to be
at intermediate risk.
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Conclusion
Initial results have shown that EBT and
especially MSCT - after i.v. injection of
contrast agent - also permit visualization of
non-calcified plaque
Partly calcified plaque in the proximal right
coronary artery visualized by multi-slice CT
MSCT
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Conclusion
Non-calcified plaque in EBT
EBT
EBT
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Conclusion
Non-calcified plaque in MSCT
30
Conclusion
Some authors have compared plaque morphology in
MSCT to intravascular ultrasound15, but the
clinical implications and the exact meaning of
non-calcified plaque in MSCT or EBBT currently
are not clear.
31
Conclusion
SUMMARY EBT and MSCT have sufficient spatial and
temporal resolution for coronary artery
visualization. Clinical studies have shown a high
prognostic value of coronary calcium for
identification of asymptomatic individuals at
increased coronary artery disease risk. The
meaning of non-calcified plques which can also be
detected (after injection of contrast agent) is
not yet clear.
32
Conclusion
SUMMARY Future clinical studies, some are
currenty being conducted, will help to define the
role of coronary calcium detection in the
clinical work-up of patients ín whom risk
stratification for coronary artery events may be
beneficial.
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Conclusion

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41-50 7. Rumberger JA, et al Coronary artery
calcium area by electron-beam computed tomography
and coronary atherosclerotic plaque area. A
histopathologic correlative study. Circulation
1995922157-2162.
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