MRI and CT of the Cardiovascular System

180 Pages·2006·12.111 MB·English

by  Charles B. Higgins, Albert de Roos

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C
ARDIOVASCULAR
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ULTIDETECTOR
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OMPUTED OMOGRAPHY
A
NGIOGRAPHY
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C
ARDIOVASCULAR
M
ULTIDETECTOR
C T
OMPUTED OMOGRAPHY
A
NGIOGRAPHY
Subha V . Raman MD
Division of Cardiovascular Medicine
Ohio State University
Columbus, Ohio
U.S.A.
Patricia V . Gr odecki MD
Cardiology Associates, PSC
Edgewood, Kentucky
U.S.A.
Stephen C. Cook MD
Division of Cardiovascular Medicine
Ohio State University

Columbus, Ohio
U.S.A.
Mario J. Gar cia MD
Mount Sinai Medical Center
New York, New York
U.S.A.
CRC Press
Taylor & Francis Group
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© 2007 by Taylor & Francis Group, LLC
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Version Date: 20130325
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Contents
Preface vii
1 Introduction 1
2 Normal Cardiac Anatomy 5
3 Abnormal Coronary Arteries 15
4 Coronary Anomalies 41
5 Artifacts 51
6 The Left Ventricle 61
7 The Right Ventricle 75
8 Valvular Heart Disease 83
9 Pericardium 99
10 Aorta 107
11 Cardiac Masses 123
12 Cardiac Veins 131
13 Peripheral Artery Disease 139

14 Congenital Heart Disease 149
Index 175
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Preface
Cardiovascular medicine has witnessed significant application of cardiovascular multidetector com-
progress over the past century, incorporating the puted tomography from the perspective of the
technical advances of each era to improve patient care of the patient. We hope that this book is use-
care. The introduction of the stethoscope, electro- ful for cardiologists and radiologists alike, as well
cardiography, roentgenography, angiography, as primary care physicians, house officers, med-
invasive hemodynamics, ultrasonography, nuclear ical students, and other health care professionals
scintigraphy, and magnetic resonance have each, who have the opportunity to use this exciting
in turn, allowed progressively greater accuracy new technology to improve diagnosis and
and precision in the diagnosis and treatment of treatment for their patients with cardiovascular
cardiovascular disease. The advent of multidetec- disease.
tor computed tomography using 64 detector rows The authors wish to acknowledge the follow-
and beyond provides the next leap forward in ing individuals for their contributions: Ogei Yar,
cardiovascular care, delivering on the promise of MD; Sanjay Patil, MD; and Silpa Kilaru, BS. We
high-resolution visualization of cardiovascular gratefully acknowledge the editorial feedback
structure and function noninvasively. from Sandra S. Halliburton, PhD, to the chapter
The goal of this book is to demonstrate the on artifacts. A special thanks is extended to Tam
clinical context within which this technology Tran, BS, whose sincere efforts throughout this
is useful for individual patient assessment, project were invaluable.
while providing relevant technical information
needed to perform cardiovascular multidetector
computed tomography. Practicing clinicians know Subha V. Raman
that patient care without technology is feasible,
Patricia V. Grodecki
but medical technology applied without clinical
Stephen C. Cook
acumen is, at best, irrelevant. Thus, in prepar-
ing this book we sought to demonstrate the Mario J. Garcia
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Chapter 1 Introduction
Computed tomography (CT) is a well-established cardiac imaging requires patient breath-hold of
technology for imaging based on the principle that 10 to 12 seconds on current generation systems,
an x-ray source and an array of detectors rotating which is feasible for most individuals including
around a target (patient) generate a set of attenua- those with cardiovascular illness.
tion information that, through filtered backprojec- Adequate patient preparation cannot be
tion reconstruction algorithms, provides the overemphasized. This is a coordinated effort
mathematical basis to generate a cross-sectional involving the scheduling staff, technologist, physi-
image. Spiral CT involves moving the rotating x-ray cian, and nurse. Documenting serum creatinine
source and the detector array as thetable advances level and history of contrast allergy is essential at
to cover a volume of tissue in the z (patient) direc- the time of scheduling. Just as with invasive
tion (Fig. 1.1), thus creating a spiral trajectory. angiography, the presence of renal insufficiency
Adding multiple detectors along the z-axis allows does not necessarily preclude cardiovascular
generation of multiple slices of axial image infor- multidetector CT (MDCT) examination; the risk of
mation during a single rotation of the gantry contrast nephropathy must be weighed against
(source-detector hardware). Greater z-axis cover- the benefit of the information to be gained from
age during a single, rapid rotation of the gantry the procedure. If clinically indicated, some degree
coupled with optimized heart rate, pitch (speed at of renal protection may be achieved with pre- and
which the table moves through thescanner relative postintravenous saline hydration. Some clinicians
to the gantry rotation speed), and reconstruction find a benefit to N-acetylcysteine administration
sector angle insures adequate overlapping of data as well. Similarly, eliciting a history of contrast
for reconstruction. Typical coverage prescribed for allergy can prompt appropriate pretreatment
to attenuate or prevent a contrast reaction in
susceptible individuals if the risk is acceptable to
both patient and referring clinician.
Even with the shortest effective gantry rotation
times currently available, inadequate heart
ratecontrol can adversely affect image quality, par-
ticularly in the setting of a highly variable heart
rate. Thus, the judicious use of medications to slow
the heart rate, assuming appropriate screening for
contraindications to such drugs, greatly increases
the likelihood of having high-quality, motion
artifact–free images for interpretation. Conversely,
in the setting of atrial fibrillation or frequent ectopy
rendering the heart rhythm highly irregular, admin-
istration of a vagolytic agent such as atropine may
be appropriate; the irregularity of the cardiac
rhythm has a more negative impact on image qual-
ity than increased heart rate alone. We seek to
achieve a heart rate during scanning of (cid:1)60 beats
per minute, though higher heart rates with no vari-
Figure 1.1 Convention for labeling the x-, y-, and ability such as those seen in the denervated
z-axes relative to the patient table (z-axis) and the post–cardiac transplant patient may also result in
scanner (x–y plane). adequate image quality. Finally, the patient with
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2 CARDIOVASCULAR MULTIDETECTOR CT ANGIOGRAPHY
a paced rhythm may warrant temporary repro- out during reformatting of the raw data if they
gramming as tolerated to render the electrocardio- result in significant artifact (Chapter 5) but are best
graphic trigger stable during scanning. Advances in dealt with before the scan with pharmacologic
multiple source scanner technology may ultimately maneuvers or pacemaker reprogramming.
improve temporal resolution to the point where Once the raw data has been acquired, it is
heart rate is no longer a factor in cardiac CT. converted to thin axial images, with all current
The scan itself is performed with peripheral 64-detector scanner platforms providing sub-
venous administration of iodinated contrast mate- millimeter spatial resolution. Reformatting to
rial. A small bolus of contrast (timing bolus) can thicker sections is helpful for maximum intensity
be used to determine the delay between intra- projection (MIP) image review. When reviewing
venous injection and the appearance of the bolus coronary artery segments with stents, one should
in the structure of interest, typically the ascending review the thinnest sections possible, as well as
aorta for coronary imaging. This delay is then images generated with both smooth and sharp
used in the volume acquisition. Alternatively, a reconstruction kernels (Fig. 1.2). Generating mul-
Hounsfield unit (HU) threshold (measurement of tiphase axial sections allows dynamic rendering of
x-ray attenuation) may be set such that once this the volume or specific structures of interest.
threshold is reached in the structure of interest, All workstation platforms allow several image
the volume scan is triggered (bolus tracking). review modes including sequential review of the
The advantage of bolus tracking is that the total axial images, simultaneous MPR image review in
volume administered is reduced, assuming that axial/coronal/sagittal planes, volume rendering,
the technologists performing the procedure have and dynamic review of multiphase data. Many
facility in recognizing when to manually start the have advocated reviewing the entire data set
scan, if necessary. During the breath-hold acquisi- from the axial plane. A complementary approach
tion, radiation dose can be minimized on the basis focused on the coronary arteries is to start from
of variable x-ray attenuation in different sections the axial plane in a three-dimensional MPR
of the body (e.g., less radiation needed in the screen, identify and evaluate the left mainstem,
neck vs. the mid-chest) or the electrocardiogram then go through the entire coronary tree segment
(ECG). Most systems now offer some form of ECG by segment [e.g., proximal left anterior descend-
dose modulation such that less radiation is ing coronary artery (LAD), mid-LAD, distal LAD,
delivered during portions of the cardiac cycle and diagonal branches] by optimizing the three
with significant motion, and these are therefore imaging planes to visualize each segment. This
less suitable for coronary reconstruction. A few insures that the entire coronary tree is evaluated
ectopic beats during the acquisition can be edited but requires more user interaction to generate

Figure 1.2 (A) MPR image of an RCA stent generated using a soft (B20f, Siemens, Erlanger, Germany)
reconstruction kernel. (B) Same RCA stent generated using a sharper (B46f) kernel demonstrates less blurring of
the stent struts.
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INTRODUCTION 3
Figure 1.3 Window width and window center are set
by the user when reviewing CT images to optimize view-
ing of lung (A) center -600, width 1600 HU; contrast-
filled structures (B), center 300, width 1099; and bone
or high-attenuation structures, (C) center 800, width
2000 HU.
adequate views of each segment. Technologists segmentation make this an ever-evolving field;
may become facile in generating thin maximum the individual practitioner should be thoroughly
intensity projections in batches along the LAD, familiar with all of the available image review
left circumflex coronary artery, and right coro- and segmentation techniques on their worksta-
nary artery, which may further simplify coronary tion platforms for those instances when the
artery assessment but does not replace careful routine approach is insufficient to answer the
interrogation of each segment by the interpreting clinical questions.
physician. Volume rendering is useful to gain an Window width and window center determine
overview of graft anatomy in patients who dynamic range and contrast when displaying CT
have undergone coronary artery bypass surgery; images; adjusting window settings allows
surveying the ascending aorta is important to management of the breadth of signal intensity
identify all grafts including those that may be information captured in the range of HU such that
occluded. Continued developments in image particular structures or tissues are more easily
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4 CARDIOVASCULAR MULTIDETECTOR CT ANGIOGRAPHY
appreciated. Thus, certain combinations are more parenchyma. Moving the center to 300 HU
suited for review of different regions as illustrated improves visualization of contrast-filled structures,
in Figure 1.3. Using a so-called lung window as seen in Figure 1.3B, and moving it still higher
with window center of -600 HU and window to a bone window centered around 800 HU
width of 1600 HU, Figure 1.3A demonstrates (Fig. 1.3C) improves delineation of bony or high-
optimal viewing of structures in the lung attenuation structures.
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Chapter 2 Normal cardiac anatomy
Anatomic considerations when reviewing cardiac straight sagittal, coronal, and axial planes. From
computed tomography (CT) images can be clas- these default planes, one may adjust the axes of
sified into axial plane anatomy and cardiac plane multiplanar reformatting to conform to the
anatomy. Serial sections from cranial to caudal cardiac planes (Fig. 2.3). The short axis is
are presented in Figure 2.1. Figure 2.2 demon- defined as being orthogonal to the interventri-
strates the cardiac chambers as viewed from cular septum from apex (beyond distal insertion
Figure 2.1 Cranial to caudal (A–D) images obtained in the axial plane. Abbreviations:AAo, ascending aorta;
DAo, descending aorta; E, esophagus; LA, left atrium; LAA, left atrial appendage; LPA, left pulmonary artery;
LV, left ventricle; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; SVC, superior vena cava.