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within the shaft body and proved to be helpful in a subset of
patients with unspecifi c symptoms after bypass surgery.
With later generations of multidetector CT systems and
improvements in spatial and temporal resolution stenosis
detection in more diffi cult situations such as the bypass anastomosis region or visualization of arterial grafts surrounded
by metal clips was enhanced. Currently, arterial grafts and
the anastomosis region of venous and arterial grafts can be
analyzed with increased diagnostic yield [ 11 – 19 ] (Figs. 10.1
and 10.2 ). Even the analysis of native vessel disease progres-
sion became more accurate with multidetector CT scanners
[ 15 ] (Fig. 10.3 ). Regarding the exclusion of high-grade ste-
noses, the negative predictive value was 100 % for bypass
grafts and 96–98 % for the native coronary arteries (grafted
or nongrafted). Only 9 % of the native coronary arteries were
unevaluable due to severe calcifi cations or motion artifacts.
A meta-analysis by Hamon et al. comprised studies using
16- and 64-slice MDCT published up to May 2007 [ 11 ]. A
total of 15 studies were included, six of which used 64-slice
CT [ 12 – 17 ]. Table 10.1 gives an overview of the diagnostic
performance of 64-slice MDCT in a total of 355 patients and
976 bypass grafts [ 11 ]. Between 87 and 100 % of the grafts
were fully assessable regarding the detection / exclusion of
angiographically signifi cant stenoses. In particular, a high
negative predictive value was obtained in the studies,
indicating the ability to reliably rule out high-grade stenoses
or obstruction of the bypass grafts using 64-slice
MDCT. More recent studies have confi rmed a negative
predictive value for ruling out high-grade bypass graft stenoses
ranging between 96 and 99 % [ 18 – 20 ]. However, depending
on the anatomy, the distal anastomosis can still be challenging to examine, and the degree of stenosis tends to be overestimated [ 18 ]. The native coronary circulation can be assessed
despite previous bypass surgery [ 19 – 21 ] (Fig. 10.4 ), how-
ever, as in a population with no previous bypass surgery,
heavy coronary calcifi cation or a small native vessel diameter can render the CT analysis diffi cult. Sensitivities for the
detection of signifi cant lesions range between 86–95 % for
distal runoffs and 86–97 % for non grafted arteries.
A recent publication demonstrated the prognostic value of
CCTA in coronary bypass patients [ 22 ]. Both bypass grafts
and native coronary arteries were analyzed regarding the
number of unprotected coronary territories (UCT). The incidence of myocardial infarction as well as the risk of death
increased signifi cantly with higher numbers of UCT. Hence,
CCTA not only provides morphologic information on the
coronary anatomy but also prognostic data.
Imaging Protocols
Most experts agree that consequential betablockade
should be undertaken with the aim of reaching heart
rates ≤ 60–65 bpm, which improves image quality due to less
motion artifacts and may reduce radiation exposure. Although
most recent scanner generations are less susceptible to motion
artifacts, practical experience dictates that this approach
yields superior visibility of coronary artery segments. The
administration of oral or intravenous nitrates for vasodilatation immediately prior to the scan is recommended. A temporal window of 60 % of the RR-interval appears to be best
suited [ 23 ]. Caudo-cranial scan direction seems to be supe-
rior in terms of image quality and radiation exposure [ 24 ].
The latest development in CT scanners led to a remarkable
decrease in radiation exposure (prospective ECG-gating,
reduced tube voltage, tube current modulation, higher acquisition speed) which is on average lower than in ICA.
Specifi c scanning protocols with the various scanners are
detailed elsewhere in this book.
Conclusions to Bypass Grafts
CCTA is increasingly used as a modality for the non-invasive
assessment of bypass graft patency and stenoses. As
compared to ICA, a small proportion of grafts remains
unassessable due to artifacts or anatomic complexity.
However, this proportion has decreased with improvements
in scanner technology. Bypass grafts as well as native
coronary arteries can be evaluated with high diagnostic
accuracy. ICA remains gold standard for defi ning coronary
Fig. 10.2 64-row MDCT 3-dimensional image reconstruction shows a
patent left internal mammary graft with two anostomoses to the fi rst
diagonal branch and left anterior descending coronary artery itself,
respectively
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bypass anatomy, but especially in patients with non-specifi c
complaints, CCTA is an excellent alternative and provides a
nice roadmap to see the origin locations and number of
patent grafts in those patients without prior recent angiography, including use of right and left internal mammaries
non-invasively.
aba
b
Fig. 10.3 64-row MDCT
3-dimensional image
reconstruction ( a ) shows a patent
left internal mammary graft to
the left anterior descending
coronary artery and the
corresponding selective
angiogram. Distal to the
anastomosis, the left anterior
descending coronary artery is
occluded; see corresponding
invasive angiographc image ( b )
Table 10.1 Results of 64-slice MDCT examination of 976 bypass grafts as documented in a meta-analysis by Hamon et al.
a
Sensitivity (%) Specifi city (%)
Positive predictive
value (%)
Negative predictive
value (%)
Positive likelihood
ratio
Negative likelihood
ratio
98.1 (96.0,99.3) 96.9 (95.3,98.1) 94.1 (91.0,96.3) 99.1 (98.0,99.7) 24.7 (12.5,47.7) 0.03 (0.01,0.06)
Numbers in parentheses = 95 % CI
a
Data from Hamon et al. [ 11 ]
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Coronary Stents
Background
The majority of percutaneous coronary angioplasties are
performed with placement of a stent in the vessel wall [ 25 ].
Most stents are made of stainless steel or cobalt-chromium,
which can both be challenging to visualize using CCTA due
to motion artifacts and “blooming”. Usual stent diameters
range between 2.5 and 4 mm. The widespread use of drug
eluting stents has signifi cantly reduced the risk of in-stent
restenosis [ 26 ]. Vessel size, stented length, co morbidities,
lesion morphology, and previous bypass surgery are predictors of higher rates of restenosis [ 26 ].
Depending on materials and size, stents can have a
widely different appearance in CCTA. A closed cell
design with a higher metal-to-surface ratio makes it more
diffi cult to visualize the stent lumen than an open cell
design. New generations of bioresorbable scaffolds
(BRS), on the other hand, made of magnesium or
polylactid polymer, are free of metal and may be visualized only by radioopaque markers at the extreme ends of
the scaffold.
Non-invasive CT Examination
Early EBCT-studies used time-density curve analysis in a
region of interest distal to the stent comparing it to the pattern
in the aorta [ 27 – 29 ]. This led to a reliable detection of com-
plete occlusions whereas high-grade and subtotal stenoses
were frequently missed because of the fact that contrast fl ow
may pass subtotal stenoses and collateral vessels may fi ll the
vessel lumen retrogradely.
Apart from motion artifacts, in vitro studies revealed further stent-related problems –– in CT imaging such as
enhancement of the stent struts (“blooming”), apparent
reduction of the stent lumen, attenuation of contrast values
ab
Fig. 10.4 Patent left internal mammary graft to the left anterior descending coronary artery with normal runoff ( a ). Patent single vein graft to the
right coronary artery with normal runoff ( b ). Bypass grafts as well as the native coronary arteries can be evaluated with good image quality
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Fig. 10.5 Ultra-high resolution images of a coronary stent using
64-row MDCT. The two left panel pictures show the stent mounted on
a vessel model placed in a phantom with realistic attenuation values.
The short arrow marks an artifi cial 30 % in-stent restenosis (produced
within the stented vessel model), the longer arrow a 50 % restenosis in
the same setting. The right panel shows a three-dimensional
reconstruction of the stent
ab
Fig. 10.6 Intermediate in-stent-stenosis of a 3.25 × 16 mm bare-metal-stent in the proximal left anterior descending artery ( a ). Corresponding
invasive coronary angiogram of the left coronary artery ( b )
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inside the lumen and beamlike artifacts adjacent to the stent
[ 30 – 33 ] (Fig. 10.5 ). Improvements in CT technology like
multi slice and dual-source scanners in recent years have
increased the accuracy of detection of in-stent stenoses
(Fig. 10.6 ). Nevertheless, stent artifacts are still problematic,
and they vary between different types of stents [ 34 ]. Several
studies have evaluated the accuracy of multislice CCTA in
diagnosing in-stent stenoses versus ICA (gold-standard)
[ 35 – 40 ], partly combined with IVUS [ 38 ] or OCT [ 39 ].
Taking all segments into account, sensitivity was 50–100 %,
specifi city 57–98 %, and negative predictive value (NPV)
96–100 %. Looking only at the assessable stents (predominantly stents > 3.0 mm), sensitivity was 86–100 %, specifi city 93–97 %, and NPV 98–100 %.
Besides patient-related aspects that impede image quality,
in particular heart rate, vessel calcifi cations, motion artifacts,
and obesity, stent diameter has been identifi ed as the most
important stent-related factor. Stent diameters of 3.0 mm or
more appear to have a signifi cantly higher diagnostic accuracy on CCTA than smaller stents [ 38 , 40 ] (Fig. 10.7 ). A
good correlation between CCTA and IVUS can be observed
in the analysis of left main coronary artery stents [ 41 ]. The
type of stent plays an essential role. A strut thickness of less
than 100 μm is associated with less artifacts und thus
improves diagnostic accuracy [ 38 ]. Due to the artifacts men-
tioned above, CCTA tends to underestimate lumen area
which may result in false positive fi ndings. On the other
hand, stent occlusions or high-grade in-stent stenoses can be
ruled out with confi dence (NPV 98–100 %). In 2010, a metaanalysis combined 14 studies assessing diagnostic accuracy
of CCTA versus ICA [ 42 ]. In total, 89 % of all stents were
assessable. Sensitivity for assessable stents was 90 %, specifi city 91 %.
Rief et al. showed improved diagnostic precision in combining CCTA with myocardial CT perfusion (CTP) [ 43 ].
CTP can add functional information concerning an in-stent
stenosis and the need for revascularization (93 % sensitivity). Fixed perfusion defi cits due to previous myocardial
infarctions result, however, in a sensitivity of 65 % and PPV
of only 33 % for CTP alone.
Recent bioresorbable stents (BRS) are hardly visible in
CCTA and, unlike metal stents, do not generate artifacts.
So far, comparative studies with other DES concerning
diagnostic yield exist only in vitro [ 34 ]. Onuma et al.
demonstrated the feasibility of CCTA and fractional fl ow
reserve (FFR) in patients after implantation of an
ABSORB BRS [ 44 ].
Imaging Protocols
Over the last decade there has been a dramatic reduction in
radiation exposure with CCTA due to improvements in CT
scanner technology and image reconstruction, e.g., iterative
reconstruction [ 45 , 46 ]. Image quality has improved due to
the use of sharp, high-resolution kernels [ 47 , 48 ]. Most
patients can be scanned with prospective ECG-triggering,
resulting in a signifi cantly lower radiation exposure compared
to the retrospective spiral mode. Xia et al. even examined
patients after stent implantation with high-pitch spiral mode
[ 49 ]. Diagnostic accuracy was equal to low-pitch spiral mode
and sequential mode, effective dose was in the range of
1.0 mSv.
Preparations for CCTA are the same for stent imaging as
for other CCTA indications and are described elsewhere in
the book.
Fig. 10.7 Patent drug-eluting stent (3.0 × 18 mm) in the proximal left
anterior descending artery
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Conclusion
Using new dual-source CT systems, coronary stents can
be visualized with high diagnostic accuracy. In stents with
diameters of 3.0 mm or more, in-stent stenoses can be
ruled out with reasonably high certainty. Importantly,
strut thickness of the stents has an impact on image quality. Stents with a small strut thickness are better assessable by CCTA than those with thicker struts. A new
quality has been introduced by bioresorbable stents,
whose materials are partly not visible in CCTA. Such
stents can only be identifi ed by distinct radio-opaque
markers at the extreme ends of the stent. ICA remains the
gold-standard for the diagnosis of in-stent stenoses. For
individual patients with prior implantation of relatively
large coronary stents (≥3 mm), CCTA may offer an
attractive alternative.
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CT Angiography Assessment for Cardiac Pathology
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© Springer International Publishing 2016
M.J. Budoff, J.S. Shinbane (eds.), Cardiac CT Imaging: Diagnosis of Cardiovascular Disease,
DOI 10.1007/978-3-319-28219-0_11
Assessment of Cardiac Structure
and Function by Computed
Tomography Angiography
John A. Rumberger
Abstract
High-resolution multi-detector CT (MDCT) scanners capable of quantitative imaging of the
heart were introduced around 2002. Initially 16-slice scanners were validated but the current state of the art is 64+-slice scanners. This chapter discusses the use of 64+-slice MDCT
for quantitative assessment of cardiac structure and function.
Keywords
Left ventricle • Systolic function • Diastolic function • MDCT • Cardiac CT
Current State of the Art
CT has traditionally oriented and displayed images parallel
or at 90° angles to the long axis of the body (i.e., transaxial,
coronal, and sagittal image planes). Such presentations oriented about the long axis of the body do not satisfy prior
established presentations of cardiac images as they do not
cleanly transect the ventricles, atria, or myocardial regions as
supplied by the major coronary arteries.
Knowledge of cardiac ejection fractions [ 1 ], absolute ven-
tricular volumes [ 2 , 3 ], and location and extent of regional
wall motion abnormalities provides valuable diagnostic and
prognostic information, and non-invasive cardiac imaging
has become the reference standard in routine clinical
practice.
The American Heart Association in 2002 [ 4 ] published
standards of myocardial segmentation and nomenclature for
tomographic imaging of the heart using non-invasive imaging modalities and divided the left ventricle (LV) into 17 segments. The nomenclature for image presentation for cardiac
CT is: the short axis, horizontal long axis, and vertical long
axis, as shown in Fig. 11.1 . These cardiac axes are very
familiar to practitioners performing SPECT or PET imaging;
for those familiar with two-dimensional echocardiography,
these correspond to the short axis, apical four-chamber, and
apical two-chamber views, respectively. These cardiac imaging planes are oriented at 90°angles relative to each other
[i.e. 3-orthogonal planes].
In order to employ CT to defi ne the cardiac chambers
and separate them from the surrounding myocardium, it is
necessary to use intravenous contrast. In general, this can
be accomplished with <100 mL of non-ionic contrast, and
it is possible to perform complete imaging of the heart
chambers, the coronary arteries, and the proximal great
vessels (aorta and pulmonary artery) in a single setting with
a single injection of contrast. Methods for contrast administration for MDCT scanning of the heart are found
elsewhere.
Orthogonal (short and various long axes) cardiac CT
images after intravenous contrast allow for identifi cation of
non-opacifi ed intracardiac thrombi (Fig. 11.2a ) and tumors
(Fig. 11.2b ) including excellent resolution of the left atrium
and the left atrial appendage (Fig. 11.3 ), allowing localiza-
tion of structures smaller than 1 mm [ 5 , 6 ]. Cardiac CT can
additionally be of assistance in defi ning thrombi or occult
occlusion of the venae cavae and other right-sided structures.
Cardiac CT can also be a primary method of defi ning intracardiac shunts such as those caused by inter-ventricular
(Fig. 11.4a ) and inter-atrial (Fig. 11.4b ) congenital defects
and other acquired defects post-infarction [ 7 ].
J. A. Rumberger , PhD, MD
Cardiac Imaging , The Princeton Longevity Center ,
Forestall Village, 136 Main Street , Princeton , NJ 08540 , USA
e-mail: jrumberger@theplc.net
1 1
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Cardiac CT can be used to quantitate left and right ventricular volumes [ 8 – 10 ], left and right atrial volumes, left and
right ventricular muscle mass [ 11 – 14 ], regional left ventricu-
lar function, wall thickening and contractility [ 15 – 17 ], rates
of diastolic fi lling of the right and left ventricles [ 16 , 18 , 19 ],
post-infarction left and right ventricular remodeling [ 20 – 24 ],
cardiac remodeling following cardiac [ 25 ] and lung trans-
plantation [ 26 ], and ejection fraction [ 27 – 30 ] in patients with
no contraindication to the use of iodinated contrast medium.
Additional applications include quantitation of uni-valvular
regurgitation [ 31 ] and assessment of infarct size [ 32 , 33 ].
The majority of these validation studies was performed in
the 1980s and 1990s using EBT and has been adapted and/or
re-validated in studies using MDCT. In most instances, these
quantitative aspects can be performed or at least wellapproximated in patients with generally normal sinus
rhythm. Since the number of cardiac cycles imaged per scan
is single (256- and 320-slice scanners) or generally limited to
<5 (64-slice scanners), quantitation may be limited in those
patients with signifi cant dysrhythmias, such as non-regular
atrial fi brillation.
All available post-processing workstations can provide
quantitative and often non-interactive (i.e., automatic)
measurements of the LV in particular. Shown in Fig. 11.5a–e ,
is the general outline of the procedure and subsequent display
of the results. Table 11.1 shows validated norms for LV
chamber size, wall thicknesses, ejection fraction, and
ventricular volumes using cardiac CT. Reproducibility of CT
in performing right and left ventricular volume and function
measurements has also been established [ 34 , 35 ].
Cardiac CT imaging using thin sections allows postprocessing of images into end-diastolic and end-systolic
short and “long” axis images at multiple ECG-phases to
facilitate identifi cation of structures and salient features of
the ventricular anatomy (Fig. 11.6 ). Using short and long
axis imaging also allows identifi cation of infarct locations
(Fig. 11.7 ). Demonstrated in this latter example is a common
CT fi nding in contrast-enhanced images from patients with
remote myocardial infarction. The “negative” contrast noted
in Fig. 11.7 is actually due to lack of contrast opacifi cation in
the infarcted region causing “contrast rarefaction.” Long axis
(both vertical and horizontal) imaging of the left ventricle
also allows for defi nition of basilar and apical infarcts, and
true- and pseudo-apical aneurysms (Fig. 11.8 ). Two-
dimensional and three-dimensional reconstruction methods,
possible in nearly an infi nite number of imaging planes, also
allows for postoperative assessment of left ventricular
aneurysectomy (Fig. 11.9 ). Global and regional details of the
LV due to ischemic cardiomyopathy and hypertrophic
cardiomyopathy using cardiac CT provide details commonly
Fig. 11.1 Standardized presentation of the heart in cardiac
CT. American Heart Association 17 segment model of the left ventricle
(LV); the orthogonal imaging planes are the horizontal long axis, the
vertical long axis, and the short axis (Reprinted from Cerqueira et al.
[ 4 ], with permission of Wolters Kluwer Health, Copyright 2002,
American Heart Association, Inc.)
J.A. Rumberger
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