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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3752_Библиотеки_им_академика_М_И_Перельмана
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noted by other imaging methods. The right ventricle (RV)
can also be imaged. Figure 11.10 shows a dilated RV in a
patient with arrhythmogenic RV dysplasia, and Fig. 11.11
shows fatty infi ltration of the RV; cardiac CT can often be an
alternative or a confi rmatory method to MRI in the evaluation
of such patients [ 36 ]. Biventricular consequences to
congenital (Fig. 11.12 ) and acquired heart disorders
(Fig. 11.13 ) can also be imaged.
Three-dimensional calipers available on all CT workstations allow for quantitative measures of ventricular dimensions in any axis (Fig. 11.14a ). Additionally, measures of
ventricular muscle thicknesses can be done on all myocardial
walls (Fig. 11.14b ). Measures of the aorta and other chambers
such as the left atrium (Fig. 11.14c ) can also be helpful and
augment data on ventricular volumes, muscle mass, and function by CT. Normal layers of fat on the epicardial surface of
a
b
Fig. 11.2 Examples of non-opacifi ed cardiac thrombus and tumor. ( a )
Modifi ed vertical long axis tomogram of the left ventricle (LV); the area
noted by the arrow is a non-opacifi ed thrombus at the LV apex. ( b )
Modifi ed horizontal long axis image of the left atrium (LA)/LV; the
non-opacifi ed area in the LA chamber is a left atrial myxoma shown at
end-systole and end-diastole: note that, during diastole, the myxoma
prolapses through the mitral valve
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Normal LA appandage LA appandage thrombus
Fig. 11.3 Defi nition of the left atrial appendage by cardiac CT. Left : a normal LA (left atrial) appendage ( dotted circle ). Right : LA appendage
with thrombus ( dotted circle )
Membranous VSD
a
Ostium secundum ASD
b
Fig. 11.4 Examples of congenital intra-cardiac shunts as shown by cardiac CT. ( a ) “Peri” membranous ventricular septal defect (VSD) as noted
by the arrow . ( b ) Jet of contrast demonstrating a left to right shunt from an ostium secundum atrial septal defect (ASD) as noted by the arrow
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Fig. 11.5 Quantitation of LV (left ventricular) function by cardiac CT.
( a ) Horizontal long axis, vertical long axis, and short axis views of the
left ventricle (LV); the line demonstrates the plane of the mitral valve:
when performing quantitative analysis, it is necessary that the LV
chamber be isolated. ( b ) Semi-quantitative edge defi nition of the
cardiac endocardial surfaces using thresholding methods; from this
information, the LV endocardial (chamber) volumes can be determined.
( c ) Semi-quantitative isolation of the LV myocardial epicardial and
septal surfaces using thresholding methods; from this information the
LV muscle mass and myocardial wall thicknesses can be determined.
( d ) Lower right of the fi gure: a color map of the myocardial surface
systolic function is defi ned to provide defi nition of regional LV function.
( e ) LV chamber volume as a function of time during the cardiac cycle;
from these data can be derived information on EF (ejection fraction),
EDV (end-diastolic volume), EDV (end-systolic volume), SV (stroke
volume), rates of systolic emptying (contractility), as well as rates of
early and late diastolic fi lling (diastolic function)
a
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b
Fig. 11.5 (continued)
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c
Fig. 11.5 (continued)
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d
Fig. 11.5 (continued)
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the heart and the outer surface of the pericardial sac provide
natural contrast and permit the examiner to reliably identify
the pericardium (Fig. 11.15 ). Contrast-enhanced CT often
allows separating chronic effusive pericarditis from gross pericardial thickening since the parietal and epicardial layers of
the pericardium have their own blood supply. CT can be used
to defi ne the entire anatomy of the pericardium and may be of
greatest value in localization of loculated effusions such as
those confi ned to the posterior areas of the heart (which are
diffi cult to defi ne using surface two-dimensional echocardiography). Tamponade can be identifi ed with CT by right atrial or
ventricular collapse or by indirect signs such as an inappropriately enlarged inferior vena cava or enlarged hepatic veins.
High-resolution images can defi ne the anatomic localization
and extent of pericardial thickening. In the evaluation of a
patient for constrictive pericarditis, CT can add considerably
to the diagnosis. CT has an advantage over traditional echocardiography in that the entire cardiac volume is imaged very
quickly, and then images of both two- dimensional and threedimensional views can be rapidly generated. Contrast is usually not required to image the pericardium, as the natural
delineation of the pericardial surface (usually 100 Hounsfi eld
Units, HU) and adjacent air (<-700 HU) is dramatic. Calcifi ed
pericardial tissue is even easier to image, as the calcifi cation is
usually in the +300−400 HU range.
Indications
The mandate for a complete cardiac CT angiogram (CCTA)
in routine clinical practice is to include quantitative cardiac
structure and function as part of each evaluation performed
for assessment of coronary plaque and lumen anatomy.
However, quantitation of cardiac function using MDCT can
only practically be performed using retrospective
ECG-gating.
Prospective ECG-gating protocols provide static images
of the heart and the coronary arteries and are appropriate if
the indication for performing 64 + -slice MDCT is solely
assessment of coronary artery anatomy. Prospectively gated
MDCT can also provide general information about cardiac
chamber sizes, general cardiac anatomy, and some evaluations of the pericardium, but cannot be used to quantitate LV
and RV systolic or diastolic function. In such instances, if LV
function is also desired for overall clinical assessment, then
alternative methods are widely available such a gated SPECT,
MRI, and two-dimensional echocardiography. Although
MRI and ultrasound provide no ionizing radiation exposure,
SPECT imaging can result in radiation exposures up to 3–5
times that of cardiac CT.
Utilization of prospective ECG gating can signifi cantly
reduce the effective radiation dose to the patient using
MDCT; however, if quantitation of LV function is also
required, a retrospective gated cardiac CT can be performed
with limited radiation by lowering the kV from 120–100
[and now even 80] and application of ECG-dose (mA)
modulation. A properly planned retrospective 64 + slice
cardiac CT can be performed with effective patient radiation
doses of 2–6 mSv versus a prospectively gated MDCT scan,
which can be done generally with effective radiation doses of
1–3 mSv (or slightly higher using 256-slice and 320-slice
scanners).
Contraindications
The contraindications to performing a retrospectively gated
MDCT for assessment of cardiac structure and function are
the same as those for performing any cardiac CT examination. Beta-blockers are almost universally applied to get resting heart rates in the range of 60 beats/min. Individuals with
reactive airways disease (e.g., emphysema, asthma) should
only be given beta-blockers under controlled conditions.
Intravenous contrast is also required, thus reduced renal function (e.g., creatinine >1.9 mg/dl) might suggest that an alternative method of evaluating the LV/RV should be considered,
but there is no absolute contraindication for MDCT cardiac
imaging in the presence of abnormal renal function.
Issues of radiation exposure of the patient during diagnostic cardiac CT examinations and have been bandied about in
the press for some time; it is of course important that this
potential hazard be considered and risk versus benefi t defi ned
by the referring physician. But the American Association of
Physicists in Medicine [AAPM] issued the following statement in 12/11 [ 37 ]:
e
120
100
80
60
40
20
0 10 20 30 40 50
% R–R
Volume (ml)
60 70 80 90 100
Fig. 11.5 (continued)
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Fig. 11.6 Example of LV (left ventricle) short axis images from the
apex to base of the heart and various ECG related phases defi ned from
end-diastole ( End D ) to end-systole ( ES ) and back to end-diastole
(end D) during a 10-phase ECG gated reconstruction of cardiac function using Cardiac CT
Table 11.1 Reference values for left ventricular size, function, and muscle mass for cardiac CT in adult women and men
a
Measurement
Women
Men
Reference
range
Mildly
abnormal
Moderately
abnormal
Severely
abnormal
Reference
range
Mildly
abnormal
Moderately
abnormal
Severely
abnormal
Septal wall
thickness (mm)
a
6–9 10–12 13–15
> 16 6–10 11–13 14–16 > 17
Posterior wall
thickness (mm)
a
6–9 10–12 13–15
> 16 6–10 11–13 14–16 > 17
LV muscle mass
(gm)
66–155 156–176 177–187 >190 96–200 201–227 228–254 >260
LV diameter
(mm)
a
39–53 54–57 58–61
> 62 42–59 60–63 64–68 > 69
LV global EDV
(ml)
60–110 111–122 123–136
> 140 70–160 161–190 191–210 > 210
LV global ESV
(ml)
20–50 51–60 61–70
> 71 25–60 61–70 71–85 > 86
LV global EF
(%)
> 55 45–54 30–44 <30 > 55 45–54 30–44 <30
Data from Rumberger et al. [ 32 ]; and Lang et al. [ 35 ]
EDV end-diastolic volume, ESV end-systolic volume, EF ejection fraction
a
End-diastole, mid left ventricle
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Fig. 11.7 Vertical long axis and mid-LV short axis images of a patient
with remote myocardial infarction. Left : vertical long axis; the arrows
point to regions of transmural infarction in the lower septal wall, apex,
and lateral wall. Right : mid-LV short axis; the arrows point to regions
of transmural infarction in the inferior septum, inferior (posterior) wall,
and lateral wall; using such presentations, estimates of myocardial
infarction size can be estimated
b
a
Fig. 11.8 Examples of left ventricular (LV) true aneurysm and
“pseudo” aneurysm using Cardiac CT. ( a ) End-systolic long axis image
of LV demonstrating LV apical aneurysm ( arrow ); ( b ) End-diastolic
long axis image of LV demonstrating dilation of LV apex and thinning
of myocardial with akinetic regional motion and “pseudo” aneurysm
( arrows )
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The American Association of Physicists in Medicine (AAPM)
acknowledges that medical imaging procedures should be
appropriate and conducted at the lowest radiation dose consistent with acquisition of the desired information. Discussion of
risks related to radiation dose from medical imaging procedures
should be accompanied by acknowledgement of the benefi ts of
the procedures. Risks of medical imaging at effective doses
below 50 mSv for single procedures or 100 mSv for multiple
procedures over short time periods are too low to be detectable
and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low
doses are highly speculative and should be discouraged. These
predictions are harmful because they lead to sensationalistic
articles in the public media that cause some patients and parents
to refuse medical imaging procedures, placing them at substan-
tial risk by not receiving the clinical benefi ts of the prescribed
procedures.
Patients unable to hold their breath for 15 s or who are
uncooperative should be avoided for cardiac CT. The presence of various dysrhythmias (frequent PACs/PVCs) can
ab
c
Fig. 11.9 Cardiac CT images of patient after left ventricular (LV)
aneurysmectomy. ( a , b ) Volume rendering presentation from lateral and
anterior views of the LV: the area of aneurysm repair is shown by the
arrows . ( c ) A maximum intensity projection (2-dimensional) of the LV
long axis showing the area of aneurysm repair: the two bright objects at
the LV apex are surgical pledgets
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