Chapter 3: Patient Assessment

3.6: Cardiovascular Magnetic Resonance Imaging

Lowie M.R. Van Assche, MD
This author has nothing to disclose.
Han W. Kim, MD
This author has nothing to disclose.
Igor Klem, MD
This author has nothing to disclose.
Raymond J. Kim, MD, FACC
Intellectual Property Rights: Inventor of delayed enhancement MRI sequence, patent owned by Northwestern Uni-
versity.

Learner Objectives
Upon completion of this module, the reader will be able to:
1. Describe the basics of image acquisition, signal processing, and image contrast.
2. Recognize important safety measures when working in a cardiac magnetic resonance (CMR) environment.
3. List the pulse sequence structure and the steps of the core cardiovascular exam.
4. Discuss the clinical applications of CMR in various cardiac pathophysiologic conditions.

Basic Principles the earth’s magnetic field. This high magnetic field strength is
generated by a superconducting magnet that is housed within
Preface the MRI scanner itself. When a patient is placed within the bore
The aim of this module is to provide an introduction to CMR of the scanner, most protons align parallel to the field, leading to
and to provide an overview of the clinical applications that are a small net magnetization vector (Figure 1, panel A).
available to clinicians today.
The next step toward image generation is the transmission of
Similar to other medical imaging techniques, magnetic reso- energy to the region of interest. With the absorption of the energy
nance imaging (MRI) acquires images through the transmission from the RF pulse, the net magnetization vector is tilted from its 3
and receiving of energy. However, unlike other modalities, MRI equilibrium orientation parallel to the static magnetic field (longitu-
offers the capability to modulate both the emitted and received dinal direction) into the transverse plane. The angle of displacement
signals so that a multitude of tissue characteristics can be ex- of the net magnetization vector is known as the flip angle (Figure
amined and differentiated without the need to change scanner 1, panel B) and may be varied depending on the pulse sequence.
hardware. As a result, from a single imaging session, one could Rotation of the precessing net magnetization vector into the trans-
obtain a wealth of information regarding cardiac function and verse plane results in the creation of a time-varying magnetic field.
morphology, myocardial perfusion and viability, hemodynamics, The signal created from a single RF excitation is illustrated in Figure
large-vessel anatomy, and so forth. However, this information 1, panel C, and is known as a free induction decay (FID).
is gathered not from a single long acquisition but rather from
multiple short acquisitions, each requiring different pulse se- Following the RF excitation, two independent relaxation
quences (software programs that drive the scanner) with specific processes return the net magnetization vector to its thermal
operational parameters and optimal settings. equilibrium (re-aligned with the static magnetic field; Figure 2).
The first process, known as longitudinal or spin-lattice relaxation,
Unfortunately, magnetic resonance (MR) vendors may use pro- describes the re-growth of the magnetization vector parallel
prietary names for the same imaging methods and settings.1,2 to the static magnetic field (Figure 2, panel A). Longitudinal
Thus, the goal of this section will be to clarify these issues and relaxation results from the transfer of energy from the excited
to provide a simple framework of the technical aspects of MRI. protons to surrounding molecules in the local environment. The
Where appropriate, issues specific to CMR will be discussed. time constant T1 describes the exponential re-growth of longitu-
dinal magnetization.
Magnetic Resonance Physics
An MRI scanner performs three basic operations (Figure 1): a) The second process, known as transverse or spin-spin relaxation,
generation of a static magnetic field, b) transmission of energy describes the decay of the magnetization vector in the trans-
within the radiofrequency (RF) range to the patient, and c) verse (X-Y) plane (Figure 2, panel B). Transverse relaxation may
receiving the MR signal following the transmission of RF energy. take place with or without energy dissipation. For example, the
Most clinical CMR scanners today have a static magnetic field transfer of energy leading to longitudinal relaxation also results
strength (Bo) of 1.5 Tesla, which is 30,000 times stronger than in transverse relaxation.

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.1

 Figure 1
Basic Operations of the MRI Scanner
3 (A) The static magnetic field (Bo). The protons align parallel or antiparallel to the static magnetic field, creating a small net magnetization vector. While
aligned to the magnetic field, the protons precess at the Larmor frequency. (B) Transmission of radiofrequency energy (RF). Energy is transmitted to the
rotating protons by a RF pulse at the Larmor frequency. RF pulses that result in a flip angle of 90° and 180° are shown (top and bottom, respectively).
The figures are presented in the rotating frame of reference, where the X-Y axes are rotating at the Larmor frequency and thus appear stationary. (C)
Generation of the magnetic resonance (MR) signal. Rotation of the net magnetization vector into the transverse plane results in the creation of a time
varying magnetic field, which in turn induces an alternating current in the receiver coil array, which is the MR signal.

Additionally, processes that simply cause proton spins to lose sional frequencies along each axis.
phase coherence without energy dissipation lead to transverse
relaxation as well. The latter mechanism most commonly results Specifically, to form a two-dimensional image, the gradients
from static or slowly fluctuating variations in the magnetic field allow the selection of the slice of interest (e.g., slice encoding
within the imaged sample. The time constant T2 describes the direction) and also modulate the MR signals to provide in-plane
exponential decay of transverse magnetization. The T1 and spatial information along the frequency encoding direction
T2 are intrinsic properties of any given tissue. Pulse sequences and the phase encoding direction. For slice selection, the slice
utilize differences in T1 and T2 to generate image contrast encoding gradient (Z-axis gradient for a transaxial slice) is played
between tissues. during RF excitation (Figure 3, panel B). Since energy deposi-
tion is only possible on-resonance, altering the center frequency
Image Acquisition and Signal Processing of the RF pulse varies the slice location. Increasing or decreas-
The MR signals following RF excitation are localized in three- ing the bandwidth of frequencies in the transmitted RF pulse
dimensional space by the use of magnetic fields generated by increases or decreases the thickness of the imaged slice.
three sets of gradient coils (Figure 3). These gradient coils alter
the strength of the static magnetic field as a linear function For spatial localization in the frequency encoding direction, the
of distance from the isocenter of the magnet in each of three X-axis gradient (for a transaxial slice) is played during MR signal
orthogonal directions (X-, Y-, or Z-axes). The variation in field receive (Figure 3, panel C). As a result, specific frequency com-
strengths across space produces differences in proton preces- ponents of the MR signal arise directly from specific spatial loca-

3.6.2 Chapter 3: Patient Assessment

 Longitudinal Recovery and Transverse Decay
Following a 90° Flip Angle Excitation
M2
A
+M0
Recovery in
Longitudinal
Direction
t

Longitudinal My
Component

Mxy
B +M0
Relaxation in the
Transverse Plane

t
Mx Mz

Transverse
Component

C
Net
Magnetization 3
Vector

Figure 2
Longitudinal Recovery and Transverse Decay Following a 90° Flip Angle Excitation
(A) Longitudinal magnetization recovery (T1 relaxation). The green growth curve demonstrates the exponential re-growth of the longitudinal component
of the net magnetization vector. (B) Transverse magnetization decay (T2 relaxation). The red decay curve illustrates the exponential decline of the transverse
component of the net magnetization vector. (C) The net magnetization vector. The vector sum of the longitudinal and transverse components that
comprise the net magnetization vector is shown.

tions along the X-axis. Spatial localization in the phase encoding Creating Contrast in Magnetic Resonance Images
direction is more difficult conceptually. The Y-axis gradient (for One of the important advantages of MRI is the ability to gener-
a transaxial slice) is played for a finite time before MR signal ate substantial soft tissue contrast by the use of pulse sequences
reception. This results in a phase shift in the precessing protons and the administration of contrast media. In general, pulse
that varies with location along the Y-axis. Importantly, each im- sequences are adjusted to emphasize differences in tissue T1
age is the result of multiple MR signal readouts, each of which and T2, which may be inherent or altered by the presence of
were preceded by a phase encoding gradient step, with slight contrast media. For instance, on pulse sequences that are T1
differences in the strength (amplitude) of the Y-axis gradient. weighted, tissues with short T1, such as fat, appear bright.

After all the phase encoding steps are completed, the raw data Traditionally, T1 weighting is accomplished by imaging with
from the scanner consists of a two-dimensional grid of data short RF repetition times (TR), which magnify differences
(also known as k-space), which is converted to an MR image in longitudinal recovery between tissues. Newer sequences
by an inverse two-dimensional Fourier transform by the image utilize magnetization preparation pulses, such as saturation
reconstruction computer.

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.3

 Figure 3
Spatial Localization of the MR Signal
(A) Orthogonal magnetic field gradients are used to localize the magnetic resonance (MR) signal. The gradients are shown oriented for a transaxial imaging
3 plane; however, the axes may be oriented orthogonally in any arbitrary direction. (B) Slice selection. The radiofrequency (RF) pulse with center frequency ωo
excites proton spins located at position zo along the direction of the gradient when applied in the presence of the linear slice select magnetic field gradient.
Changing the RF pulse center frequency to ω1 or ω2 shifts the location of the imaging slice to z1 or z2, respectively. (C) Frequency encoding. During MR
signal receive, the frequency encoding gradient alters the frequency of the MR signal depending upon its position along the direction of the gradient. The
MR signal from any given position has a unique frequency. In the example shown, frequency ωL (or ωH) is an MR signal from position XL (or XH).

or inversion pulses, to create improved T1 contrast (Figure 4). making it strongly paramagnetic. When administered, it primarily
An inversion (180°) compared with saturation (90°) prepulse shortens the T1 in the tissues where it is distributed (Figure 5).
provides greater T1 weighting, but the sequence is more prone
to artifacts when gating is irregular (either because of electro- Cardiac Magnetic Resonance Safety
cardiogram [ECG] artifact or arrhythmia). The CMR environment has the potential to pose serious risks
to patients and facility staff in several ways. Injuries may result
T2-weighted pulse sequences are traditionally created using rela- from the static magnetic field (projectile impact injuries), very
tively long echo times (TE). With long TE (on the order of tissue rapid gradient field switching (induction of electric currents
T2), there is increased separation of different T2 relaxation curves, leading to peripheral nerve stimulation), RF energy deposition
which translates into larger differences in image intensity. (heating of the imaged portion of the body), and acoustic noise.

The administration of intravenous contrast agents can also be used The risks of projectile injuries from the static magnetic field
to affect image contrast by altering tissue T1 and/or T2. The mag- are minimized by the institution of policies that strictly limit
nitude of T1 and/or T2 change depends on the specific relaxivities access to the magnet room. For instance, patients are screened
of the contrast media, the distribution characteristics (i.e., intravas- extensively prior to imaging, and all facility personnel undergo
cular, extracellular, or targeted to a specific tissue), and tissue perfu- dedicated training in MR safety. The use of MR “safe” or com-
sion. Gadolinium-based contrast media is commonly used in CMR. patible equipment (e.g., stethoscopes, wheelchairs, gurneys,
Gadolinium is a lanthanide metal with seven unpaired electrons, oxygen tanks, infusion pumps, monitors, etc.) with clear labeling
of such in the scanner area reduces this risk further.

3.6.4 Chapter 3: Patient Assessment

 Magnetization Preparation Pulses to Create T1 Contrast
A Saturation Recovery
Mz
Myocardium with normal perfusion has
short T1 (recovers fast, looks bright)
+M0 c
b
Myocardium with reduced perfusion has
long T1 (recovers slowly, looks dark)
a

time

Acquire one entire image

(when curves have maximum separation)

B Inversion Recovery
Mz
Nonviable (infarcted) myocardium has
short T1 (recovers fast, looks bright)
+M0
Viable (normal) myocardium has
long T1 (recovers slowly, looks dark)
time

-M0 Inversion Time (IT) to “null”

normal myocardium

Acquire one segment

(when normal myocardium is nulled)

3
Figure 4
Magnetization Preparation Pulses to Create T1 Contrast
(A) Saturation recovery. A 90˚ radiofrequency (RF) pulse followed by strong gradient spoilers reduces the net magnetization to zero. Magnetization recovers
depending on tissue T1. For instance, immediately following intravenous bolus administration of gadolinium contrast, myocardium with normal perfusion
has substantial uptake of gadolinium, thus has short T1, and appears bright on saturation recovery perfusion magnetic resonance imaging (MRI). In
comparison, myocardium with reduced perfusion has diminished uptake of gadolinium, longer T1, and appears dark. Ideally, data readout should follow
the saturation pulse at a specific time (time point b rather than time point a or c) to achieve maximum separation between the T1 relaxation curves of
normal and abnormal myocardium. (B) Inversion recovery. An 180˚ RF pulse inverts the longitudinal magnetization from the +z-axis to the –z-axis. Often
used in infarct imaging, the time between the inversion pulse and the center of data readout (inversion time or IT) is selected to accentuate the differences
of gadolinium uptake in normal and infarcted myocardium. Specifically, the inversion time is chosen so that the center of image readout (for linear k-space
acquisition) occurs when the T1 relaxation curve of normal myocardium crosses zero (e.g., nulled). Note that with this inversion time, the T1 relaxation
curve of infarcted myocardium is above the zero crossing, and infarcted tissue is bright.

The Food and Drug Administration (FDA) has placed limits on Patients with medical devices or implants may face additional
the rate of change of gradient magnetic fields (e.g., the slew potential hazards, including device heating, movement, or mal-
rate) and the amount of RF energy (e.g., specific absorption rate function. For example, ferromagnetic aneurysm clips or electronic
[SAR]) that can be transmitted to patients. All scanners monitor medical devices (e.g., neural stimulators, insulin pumps) are strict
the slew rate and calculate the SAR to help prevent nerve stimu- contraindications to MRI. However, there is a specific subset of
lation and heating. Acoustic noise of 100 dB or more is gener- patients with metallic implants/devices that may safely undergo
ated from the vibration or motion of the gradient coils during MRI. A comprehensive list of devices/implants that are compatible
image acquisition. The use of protective hearing devices, such with undergoing MRI scanning may be found elsewhere.3,4
as headphones or earplugs, reduces noise to levels that do not
result in hearing impairment or patient discomfort. In practice, Regarding cardiac devices, it is important to note that prosthetic
continuous communication with the patient throughout the valves and coronary artery stents are now considered safe for
exam is important for patient comfort and safety. MRI scanning.3-5 Indeed, recently, the FDA approved the use

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.5

 Figure 5
The Effect of Gadolinium Contrast on T1- and T2-Weighted Imaging
Prior to contrast administration, there are minimal differences in inherent tissue T1 and T2 between normal and infarcted myocardium; thus, infarction is
poorly delineated (top panel). After gadolinium administration, the T1 of infarction (although not T2) is markedly shortened, leading to clear delineation on
3 the T1-weighted image (bottom panel). T1-weighted images were acquired using an inversion recovery gradient echo sequence. T2-weighted images were
acquired using a dark-blood turbo-spin echo sequence. Approximate T1 and T2 times are for 1.5 T scanners.

of MRI immediately after the implantation of paclitaxel and patients with severe chronic renal disease (e.g., glomerular filtration
sirolimus drug-eluting stents. At most institutions, MRI scans rates [GRF] ≤30 ml/min/1.73 m2), particularly those undergoing
are not performed in patients with implanted pacemakers or peritoneal dialysis or hemodialysis.
defibrillators because of the potential risk of device malfunction,
excessive device or lead heating, or induction of currents within Other at-risk groups include patients with acute renal failure (where
the leads. Recently, however, a few preliminary reports have estimated GFR may not accurately reflect renal function), patients
emerged suggesting that MRI may be possible in patients with with hepatorenal syndrome, and patients in the peri-transplant
modern pacemakers and defibrillators in whom the benefits are period after liver transplantation. A policy statement regarding the
deemed greater than the risks.6-10 In patients in whom devices use of gadolinium contrast agents in the setting of renal disease
have been extracted but the leads remain (both transvenous has been published by the American College of Radiology.12
or epicardial), MRI is contraindicated, as the risk of heating or
induction of currents may be higher. The Cardiovascular Exam
Recently, it was reported that a small subset of patients with end- Pulse Sequence Structure
stage renal disease receiving gadolinium contrast may be at risk for An individual pulse sequence is a combination of RF pulses,
developing nephrogenic systemic fibrosis (NSF).11-15 NSF is charac- magnetic gradient field switches, and timed data acquisitions,
terized by an increased tissue deposition of collagen, often result- all applied in a precise order, which results in either accentuation
ing in thickening and tightening of the skin and predominantly in- or suppression of specific biological parameters. A simple way to
volving the distal extremities. Additionally, fibrosis may affect other conceptualize pulse sequences is to consider them as consisting
organs, including skeletal muscles, lungs, pulmonary vasculature, of two separate elements: 1) the imaging engine and 2) associ-
heart, and diaphragm. Thus, gadolinium contrast agents should be ated modifiers.16 The imaging engine is a required component
utilized cautiously (and alternative tests should be considered) in that provides information regarding the spatial relationship of

3.6.6 Chapter 3: Patient Assessment

Figure 6
MRI Pulse Sequence Structure 3
The magnetic resonance imaging (MRI) pulse sequence can be considered as composed of two separate elements: the imaging engine and modifiers.
Typical images using different imaging engines and modifiers are shown at the bottom. All images are of the same short-axis spatial location. See text for
further information.
Modified with permission from Shah DJ, Judd RM, Kim RJ. Technology insight: MRI of the myocardium. Nat Clin Pract Cardiovasc Med 2005;2:597-605.
permission.

objects within the imaging field (i.e., is the main component each frame comprising 35-45 ms. Cine-MRI may be acquired
that produces the image). Modifiers are optional components in either a “real-time” single-shot mode or via a segmented
that can be added to the imaging engine either individually or k-space data acquisition approach (Figure 6). Real-time cine-
in combination, to provide specific information regarding tissue MRI can be performed during free breathing and with minimal
characteristics or to speed imaging. Figure 6 lists some of the patient cooperation, making it ideal for children or patients who
more commonly used imaging engines and modifiers in CMR. have difficulty following breathing instructions. Segmented cine-
MRI is performed during a breath-hold and offers substantial
The Core Exam improvement in image quality with superior spatial and tempo-
Figure 7 depicts the protocol steps associated pulse sequences, ral resolution compared to real-time imaging. Thus, in clinical
and the timeline of a typical core exam that includes stress test- practice, segmented imaging is usually preferred.17,18
ing. Depending on the CMR study indication and the findings
during the course of the examination, additional elements may In segmented acquisition, data are collected over multiple
be added to fully investigate the clinical question. consecutive heart beats (typically 5-10). During each heartbeat,
blocks of data (segments) are acquired with reference to ECG
Function/Volumes timing, which represent the separate phases or frames of the
The goal of cine imaging is to capture a movie of the beating cardiac cycle. Following the full acquisition, data from a given
heart in order to visualize its contractile function. Typically, be- phase, collected from the multiple heartbeats, are combined to
tween 20 and 25 cine frames is acquired per cardiac cycle, with form the complete image of the particular cine frame.

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.7

 Timeline and Potential Components of a
Multi-Technique CMR Examination for Cardiac Imaging
Time CMR Technique Comments
(minutes) Includes
0
• Cardiac function, volumes, mass
5 Cine • Valvular morphology, stenosis, regurgitation
• Pericardium
Optional
• Dark and bright-blood tomographic imaging of heart & great vessels
Adenosine 3-4 minutes

Morphology
• T2-weighted imaging of acute injury
13 • T2* imaging for assessment of myocardial iron
16 Performed in appropriate patients
contrast Stress
• Post-MI risk stratification
injection Perfusion
• Ischemia evaluation
17
15 min interval between stress/rest perfusion
Additional • Velocity/flow imaging for valvular disease and cardiac output
25 Imaging • Whole-heart coronary MRA (may be performed prior to contrast)
• Additional CINE imaging
32 Performed in appropriate patients
contrast Rest • Improves specificity of stress perfusion imaging
injection Perfusion
• Quantification of myocardial blood flow reserve
33
Typical Sequence
5-minute Delay
38 • 2D or 3D, segmented (high resolution and high SNR)
Delayed Useful Additional Sequences
Enhancement • Single shot (rapid, no breath-hold required, resistant to arrhythmias)
• Long inversion time (~600 ms)
45 (useful for thrombus detection and “no-reflow” regions in acute MI)
3

Figure 7
Timeline and Potential Components of a Multi-Technique CMR Examination for Cardiac Imaging
CMR = cardiac magnetic resonance; MI = myocardial infarction; MRA = magnetic resonance angiography; SNR = signal-to-noise ratio.
Reproduced with permission from Kim HW, Farzaneh-Far A, Kim RJ. Cardiovascular magnetic resonance in patients with myocardial infarction: current and
emerging applications. J Am Coll Cardiol 2009;55:1-16 .

Perfusion at Stress and Rest allow adequate LV coverage as well as reduced motion arti-
The goal of perfusion imaging is to create a movie of the transit facts.21 In general, image readout times more than ~120 ms can
of contrast media (typically gadolinium based) with the blood lead to substantial motion artifacts in images acquired during
during its initial pass through the left ventricular (LV) myocar- periods of the cardiac cycle in which there is rapid LV motion.
dium (i.e., first-pass contrast-enhancement). Usually 4-5 short-
axis views are obtained every heartbeat with a total of 40-60 Viability and Infarction
heartbeats consisting of the entire first-pass (Figure 8). The goal of delayed-enhancement MRI (DE-MRI) is to create
images with high contrast between abnormal myocardial tissue,
A variety of pulse sequences are in use today for perfusion which generally accumulates excess gadolinium (following
MRI, and the pace of development is rapid. Common imaging intravenous administration), and normal tissue in which gado-
engines are steady-state free-precession (SSFP), gradient-recalled linium concentration is low. This is currently best achieved using a
echo (GRE), and GRE-echo-planar imaging (GRE-EPI) hybrid segmented GRE imaging engine with inversion recovery prepulse
sequences (Figure 6). Virtually all sequences include a saturation modifier to provide very strong T1 weighting.22-26 A parallel
prepulse modifier to provide T1 weighting and to accentuate re- imaging19,20 modifier can be used to shorten acquisition time.
gional differences in myocardial gadolinium concentration (Fig- Imaging is performed approximately 5 minutes after rest perfu-
ure 4, panel A). Since images are acquired in single-shot mode, sion imaging or 10-15 minutes after a one-time intravenous
a parallel imaging19,20 modifier is essential to speed imaging and gadolinium dose of ~0.15 mmol/kg if stress-rest perfusion
3.6.8 Chapter 3: Patient Assessment
 Figure 8
First-Pass Perfusion MRI
Image Acquisition
Images are acquired serially at
multiple slice locations (usually
4-5 short-axis views for left
ventricular coverage) every
heartbeat to depict the passage
of a compact contrast bolus as
it transits the heart. Example
images of one slice location are
shown at several representative
time points: before arrival of
contrast (frame 1); contrast in
RV cavity (frame 12); contrast
in LV cavity (frame 22); peak
contrast in LV myocardium
(frame 30), showing normal
perfusion in the septum (open
arrowhead) and abnormal
perfusion in the inferolateral
wall (solid arrowhead); and
the contrast wash-out phase
(frame 50).

imaging is not performed. Short- and long-axis views in the time. The acronym commonly used is “TI,” but to avoid confu-
identical planes used for cine imaging are obtained during sion with “T1” (longitudinal relaxation time), the authors prefer
repeated 6-10 second breath-holds. Data acquisition (readout the use of “IT.”
period) is timed with the ECG in mid-diastole to minimize cardiac
motion. Only every other heartbeat is used for data collection to Figure 4, panel B demonstrates that to maximize contrast
allow for adequate recovery of longitudinal relaxation between between infarcted and viable myocardium, IT should be set to
inversion pulses (if bradycardia is present, imaging can occur every when the relaxation curve of viable myocardium crosses zero. In
heartbeat).27 general, once the optimal IT has been determined, no adjust- 3
ment is necessary if DE-MRI is completed in approximately 5
Following an intravenous bolus, gadolinium distributes through- minutes. However, it is important to keep in mind that gado-
out the intravascular and interstitial space while simultaneously linium gradually washes out of viable myocardium, and IT will
being cleared by the kidneys. In normal myocardium, where the need to be adjusted upward if DE-MRI is performed at multiple
myocytes are densely packed, tissue volume is predominately time points after contrast administration.27
intracellular (~75-80% of the water space28). Since gadolinium
is unable to penetrate intact sarcolemmal membranes,29 the Compared with other imaging techniques that are currently
volume of distribution is small, and one can consider viable used to assess myocardial viability, an important advantage of
myocytes as actively excluding gadolinium media. DE-MRI is the high spatial resolution. With a standard imple-
mentation, a group of 10 hyperenhanced pixels (voxel resolu-
In acute myocardial infarction (MI), myocyte membranes are tion 1.9 x 1.4 x 6 mm) in a DE-MRI image would represent an
ruptured, allowing gadolinium to passively diffuse into the infarction of 0.16 g or a region 1,000th of the LV mass.26 This
intracellular space. This results in an increased volume of distri- level of resolution, which is more than 40-fold higher than
bution for gadolinium and thus increased tissue concentration single-photon emission computed tomography (SPECT), allows
compared with normal myocardium.30-32 Similarly, in chronic visualization of even microinfarcts that cannot be detected by
infarction, as necrotic tissue is replaced by collagenous scar, the other imaging methods.25,33
interstitial space is expanded and gadolinium tissue concentra-
tion is increased.32 Recently an ultrafast, real-time version of DE-MRI has been
developed that can acquire snap-shot images during free-
Higher tissue concentrations of gadolinium lead to shortened breathing.34,35 This technique utilizes an SSFP imaging engine
T1 relaxation. Thus, when the parameters are set properly, T1- in single-shot mode with parallel imaging acceleration and pro-
weighted sequences such as those used for DE-MRI can depict vides complete LV coverage in under 30 seconds. This technique
infarcted regions as bright or “hyperenhanced,” whereas viable could be considered the preferred approach in more acutely ill
regions appear black or “nulled” (Figure 5). One of the most patients who are unable to breath-hold or who have an irregular
important parameters to set correctly is the time between the
inversion prepulse and data readout, known as the inversion

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.9

 Figure 9
ECG Gated Velocity-
Encoding MRI
Analogous to cine imaging,
each velocity-encoded
image (top row of images)
corresponds to a cardiac
phase, and gating to the
electrocardiogram (ECG) is
necessary. On the images,
white represents maximal
velocity (in this case across the
aortic valve, red arrow). Black
represents flow in the opposite
direction (in the descending
thoracic aorta, blue arrow).
Grey represents no flow. The
bottom row demonstrates
the corresponding cine-MRI
images.
MRI = magnetic resonance
imaging.

heart rhythm. However, compared with standard segmented monly used in cardiovascular imaging is black-blood HASTE
DE-MRI, sensitivity for detecting MI is mildly reduced, and the (half-Fourier single-shot TSE). With SSFP or HASTE morphologic
transmural extent of infarction may be underestimated.35 imaging, the entire thorax can be imaged in multiple orthogonal
views in less than 2 minutes without breath-holding.
Additional Imaging
Morphology T2-Weighted “Edema” Imaging
3 Occasionally, additional structural/anatomical information is T2-weighted imaging has shown promise in assessing acute
necessary to fully investigate the clinical question, such as in the inflammatory processes.37 In the setting of myocardial necro-
setting of congenital heart disease, cardiac masses, or patients sis, such as in acute MI or myocarditis, tissue myocardial water
with aortic root dilation on initial three-chamber cine-MRI. In content increases substantially within the region of necrosis.38
general, a “morphology” scan consists of a series of parallel The presence of tissue edema results in a longer intrinsic T2 for
slices, which “bread-loaf” the anatomical region of interest. infarcted myocardium (60-65 ms) compared to that of normal
Although any orientation may be imaged, usually axial, sagittal, (45-50 ms).39 Thus, the goal of T2-weighted imaging is to utilize
or coronal planes (or all three) are chosen first. the differences in T2 between normal and necrotic myocardium
to create tissue contrast.
In order to quickly provide substantial anatomical coverage,
morphology imaging is primarily performed in single-shot mode Flow/Velocity
using either an SSFP or TSE imaging engine. The SSFP sequence Depending on the clinical question, the core exam may include
is similar to that used for real-time cine-MRI, but it has been velocity-encoded cine imaging (VENC-MRI) to measure blood
altered to produce a stack of images that progresses through velocities and flows in arteries and veins and across valves and
space rather than a cine movie loop at a single location. In its shunts. Also known as phase-contrast velocity mapping, the un-
native form (without additional modifiers), SSFP produces im- derlying principle is that signal from moving blood or tissue will
ages in which blood in the cardiac chambers and vasculature undergo a phase shift relative to stationary tissue, if a magnetic
appear bright; thus, it is known as a “bright-blood” technique. field gradient is applied in the direction of motion.

To first order, SSFP images are T2/T1 weighted.24 In contrast, The goal of VENC-MRI is to produce a cine loop across the car-
spin-echo based sequences such as TSE produce images in diac cycle, where on any given frame, pixel intensity is propor-
which flowing blood is dark; thus, these are known as “black- tional to blood velocity. Generally displayed using a greyscale,
blood” techniques. However, blood signal suppression may be white corresponds to maximum flow in one direction, black to
incomplete, and a black-blood modifier, which consists of a maximum flow in the opposite direction, and mid-grey indicates
double-inversion prepulse,36 is often added to improve blood that flow is absent (Figure 9). Although blood velocity can be
nulling or blackening. A single-shot version of TSE that is com- measured in any arbitrary direction, it is usually assessed in refer-

3.6.10 Chapter 3: Patient Assessment

 Comparison of Velocity-Encoded MRI
and Doppler Echocardiography

Imaging Characteristic Velocity-Encoding MRI Doppler Echocardiography

Imaging during free breathing Limited Yes Table 1

Comparison of Velocity-Encoded MRI
Imaging during arrhythmias Limited Yes and Doppler Echocardiography
Temporal resolution ~50 ms* <10 ms *Given temporal resolution is for breath-hold
imaging. Temporal resolution may be significantly
Peak velocity location Yes Location ambiguity (CW Doppler) improved for nonbreath-hold imaging, but
artifacts due to respiratory motion artifact may
Angle dependence Yes, 20 degrees Yes, 20 degrees
be prominent.
Imaging planes Any Echocardiographic windows †Conduit cross-sectional area is estimated from
diameter measurement.
Blood flow profile Directly measured Flat profile assumed
CW = continuous-wave;
Flow quantification En face In-plane†
MRI = magnetic resonance imaging.

ence to the imaging plane. Encoding velocity in the slice gradi- Coronary Magnetic Resonance Angiography
ent direction allows measurement of through-plane velocities, Coronary MR angiography (MRA) may be used to directly visual-
and encoding in either the frequency or phase-encode gradient ize coronary anatomy and morphology. However, coronary MRA
directions allows in-plane measurement of velocity components is technically demanding for several reasons. The coronary arteries
directed either vertically or horizontally within the image plane. are small (3-5 mm) and tortuous compared with other vascular
beds that are imaged by MRA, and there is nearly constant motion
VENC-MRI is commonly performed using a segmented GRE imag- during both the respiratory and cardiac cycles. Thus, precise assess-
ing engine during a patient breath-hold. However, the sequence ment of stenosis severity and visualization of distal segments are
is modified to measure the effects of a magnetic field gradient on difficult, leading to intermediate sensitivity and specificity values
the precessing protons within flowing blood. Optimizing the max- for the detection of coronary artery disease (CAD) in validation
imum velocity that can be measured—which is inversely related studies.40 Currently, the only clinical indication that is considered
to gradient strength (for a constant application time)—is impor- appropriate for coronary MRA is the evaluation of patients with
tant. Setting the maximum velocity too low will lead to aliasing; suspected coronary anomalies.41
3
whereas, setting it too high will lead to more noise or inaccuracy
in the velocity measurement. Retrospective rather than prospec-
Clinical Applications
tive ECG gating is preferred to allow data collection throughout
the entire cardiac cycle, including end-diastole. Coronary Artery Disease and Ischemia
A number of CMR approaches exist for the detection of CAD.42
Although VENC-MRI appears analogous to Doppler echocardiog-
Each of these techniques exploits specific anatomical or physi-
raphy, there are important differences (Table 1). For instance, an
ological properties that occur as a result of CAD (Table 2). How-
advantage of VENC-MRI is that blood flow through an orifice is
ever, clinically, the most widespread approach for evaluating
directly measured on an en-face image of the orifice with through-
CAD is stress testing with imaging of either myocardial contrac-
plane velocity encoding. With echocardiography, there are two
tion or perfusion.
limitations. First, the blood flow profile is not directly measured, but
assumed to be flat (i.e., velocity in the center of the orifice is the Analogous to echocardiography, cine-MRI during dobutamine
same as near the edges) so that, hopefully, one sampling velocity stimulation can be used to detect ischemia-induced wall motion
would indicate average velocity. Second, the cross-sectional area of abnormalities. Dobutamine cine-MRI may yield higher diagnos-
the orifice is estimated from a diameter measurement of the orifice tic accuracy than dobutamine echocardiography,43 and can be
at a different time from when Doppler velocity was recorded using effective in patients not suited for echocardiography due to poor
a different examination (M-mode or 2D imaging). acoustic windows.44

On the other hand, VENC-MRI has some disadvantages. Perhaps Recent data suggest that the presence of inducible ischemia by
most importantly, VENC-MRI is not performed in real time and this technique predicts subsequent cardiac mortality.45-49 As a
requires breath-holding to minimize artifacts from respira- result, the 2006 appropriateness criteria for cardiac computed
tory motion. One consequence is that it is difficult to measure tomography and cardiac MRI from the American College of
changes in flow that occur with respiration. Cardiology Foundation and other societies has specified that
the use of dobutamine cine-MRI is appropriate for the detec-
tion of CAD in symptomatic patients with intermediate pretest

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.11

 Cardiovascular Magnetic Resonance Techniques
Table 2 for the Detection of Coronary Artery Disease
Cardiovascular Magnetic Resonance
Techniques for the Detection of Clinical
Physiologic Substrate CMR Technique Stress Test1 Application
Coronary Artery Disease
Coronary anatomy Coronary MRA None +2
MRI = magnetic resonance imaging; and morphology
MRA = magnetic resonance angiography;
BOLD = blood oxygenation level-dependent; Coronary artery blood Velocity-encoding MRI Adenosine/dipyridamole -3
flow/velocity
ATP = adenosine triphosphate.
1
Rest studies alone may provide some Deoxygenated BOLD MRI Adenosine/dipyridamole -
information regarding the presence of coronary hemoglobin content

artery disease.
Phosphocreatinine/ 31P-spectroscopy Handgrip exercise -
2
For assessment of coronary anomalies and ATP content
patency of coronary bypass grafts.
Ventricular function Multi-phase cine-MRI Dobutamine ++
3
Recent studies suggest potential utility for
assessment of coronary bypass patency and in- Myocardial perfusion Dynamic first-pass perfusion Adenosine/dipyridamole ++
contrast-enhanced MRI
stent restenosis.

Figure 10
3 Importance of Spatial Resolution in
Stress Perfusion Imaging
Patient has an inducible perfusion defect
limited to the subendocardial portion of the
septal wall (black arrow) caused by an ostial
stenosis (white arrow) of a septal branch of the
left anterior descending coronary artery.

probability, who have uninterpretable ECGs or are unable to such as radionuclide imaging, perfusion MRI has many potential
exercise.41 From a practical standpoint, several logistical is- advantages: more than an order of magnitude improvement in
sues regarding patient safety and adequate monitoring require spatial resolution (typical voxel dimensions, MRI 3.0 x 1.8 x 8
thorough planning and experienced personnel. Perhaps in part mm = 43 mm3 vs. SPECT 10 x 10 x 10 mm = 1000 mm3; Figure
because of these issues, only a few centers worldwide routinely 10); the ability to identify regional differences in flow over the
perform this technique. full range of coronary vasodilation (i.e., no plateau in signal at
high flow rates, as seen with radionuclide tracers55,56; Figure 11);
First-pass perfusion MRI during adenosine vasodilation is rapidly the lack of ionizing radiation; and an examination time of 30-45
becoming the stress test of choice in clinical CMR centers. Perfu- minutes versus 2-3 hours.
sion MRI is promising for several reasons. Decreased perfusion is
the first step in the ischemic cascade. Therefore, techniques that The diagnostic performance of stress perfusion MRI has been
assess perfusion have the potential to be more sensitive than evaluated in a number of studies in humans.57-75 Overall, these
techniques that assess later steps.50-54 studies have shown good correlations with radionuclide imag-
ing and x-ray coronary angiography. Table 3 summarizes the
Logistically, stress perfusion imaging is quick and simple. The published stress perfusion MRI studies in humans with coro-
duration of adenosine infusion is short (~3 minutes), and direct nary angiography comparison. A total of 34 studies have been
access to the patient is limited only during imaging of the first completed, consisting of more than 2,800 patients with known
pass (~45 seconds). Compared with competing technologies or suspected CAD. On average, the sensitivity and specificity

3.6.12 Chapter 3: Patient Assessment

 Comparisons of Perfusion MRI, Radionuclide, and Microsphere Flows
A 100 B 100

Mibi SPECT RRF

75 75
MRFP RRF

50 50

25 25
y = 0.93x + 4.3 y = 23 Ln(x) - 11
r2 = 0.77 r2 = 0.74
0 0
0 25 50 75 100 0 25 50 75 100
Microsphere RRF Microsphere RRF

C 100 D 100

In-and Ex-Vivo Mibi RRF

Thallium SPECT RRF

75 75

50 50 SPECT
y = 24 Ln(x) - 16
r2 = 0.75
25 25 Well Counting
y = 28 Ln(x) - 35 y = 22 Ln(x) - 2
r2 = 0.70 r2 = 0.80
0 0
0 25 50 75 100 0 25 50 75 100
Microsphere RRF Microsphere RRF

Figure 11
Comparisons of Perfusion MRI, Radionuclide, and Microsphere Flows
Magnetic resonance imaging (MRI) signal intensity-time curves were linearly related to reference microsphere flows over the full range of vasodilation. 3
Relationships between 99mtechnetium (Tc)-sestamibi and 201thallium (Tl) activity and microsphere flows were curvilinear, plateauing as flows increased. Data
suggest that perfusion MRI, unlike radionuclide imaging, has the potential for detecting stenoses, producing only moderate limitations in flow reserve. (A)
Normalized magnetic resonance first-pass perfusion (MRFP) imaging and full-thickness microsphere relative regional flows (RRF). (B) Normalized 99mTc-
sestamibi and full-thickness microsphere RRFs. (C) Normalized 201Tl and full-thickness microsphere RRFs. (D) In-vivo single-photon emission computed
tomography (SPECT) and ex-vivo well counting values of 99mTc-sestamibi versus microsphere RRFs.
Reproduced with permission from Lee DC, Simonetti OP, Harris KR, et al. Magnetic resonance versus radionuclide pharmacological stress perfusion imaging
for flow-limiting stenoses of varying severity. Circulation 2004;110:58-65.

of perfusion MRI for detecting obstructive CAD were 85% and test sensitivity and/or specificity.76,77 Importantly, in many studies
81%, respectively. The 2006 appropriateness criteria for cardiac after the data were collected, several methods of analysis were
computed tomography and cardiac MRI from the American Col- tested and different thresholds for test abnormality were ap-
lege of Cardiology Foundation and other societies has indicated praised. For these studies, the reported sensitivity and specificity
that the use of stress perfusion MRI is appropriate for detec- values are optimistic since the endpoints were chosen retrospec-
tion of CAD in symptomatic patients with intermediate pretest tively and they represent optimized values.
probability and who have uninterpretable ECGs or are unable to
exercise.41 Several practical issues should also be considered when evaluat-
ing these studies. The studies in Table 3 are fairly heterogeneous
Despite the mostly favorable results of these studies, a number in terms of the protocols and methods employed. In part, this
of issues should be considered. Some studies are of limited is a reflection of the rapid pace of pulse sequence development
clinical applicability because they required central venous cath- over this time frame. Thus, earlier studies may have utilized
eters,61 imaged only 1 slice per heartbeat,61,65 or excluded pa- pulse sequences and/or imaging protocols that are no longer
tients with diabetes.70 Many studies had small sample sizes—11 commonly used in a clinical setting, and some reports may
had 30 or fewer patients. Most included patients already known not be directly comparable. For instance, the dose of gado-
to have CAD or known to have prior MI. In these studies, there linium contrast administered has been variable (over a sixfold
is pretest referral or “spectrum” bias, which can artificially raise range—0.025-0.15 mmol/kg). Second, several studies used a

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.13

 Stress Perfusion MRI Studies in Humans With
Coronary Angiography Comparison
Pts with X-Ray
Number known MRI Gadolinium Pulse- Angiography Analysis
Year Author Ref. of Pts. CAD Perfusion Dose Sequence (CAD Method2 Sensitivity Specificity
excluded Protocol1 (mmol/kg) definition)

1993 Klein 1
5 no Stress 0.05 IR-GRE >50 prospective 81* 100*

1994 Hartnell 2
18 no Rest/Stress 0.04 IR-GRE ≥70 prospective 83 100

1994 Eichenberger 3
10 no Rest/Stress 0.05 GRE >75 retrospective 44* 80*

2000 Al-Saadi 4
34 yes Rest/Stress 0.025 IR-GRE ≥75 prospective 3
90 83

2001 Bertschinger 5
14 no Stress 0.1 SR-EPI ≥50 retrospective 85 81

2001 Schwitter 6
48 yes Stress 0.1 SR-GRE-EPI ≥50 retrospective 87 85

2001 Panting Stress Perfusion MRI Studies in Humans With

7
22 no Rest/Stress 0.05 IR Spin Echo-EPI >50 retrospective 79 83

Coronary Angiography Comparison (2 of 3)

2002 Sensky 8
30 no Rest/Stress 0.025 IR-GRE >50 prospective 93* 60*
2002 Ibrahim 9
25 no Rest/Stress 0.05 SR-GRE-EPI >75 retrospective 69* 89*
2003 Chiu 10
13 no 4
Rest/Stress 0.05 IR-SSFP >50 NS 92* 92*
2003 Ishida 11
104 Ptsno
with Stress/Rest 0.075 SR-GRE-EPI ≥70
X-Ray prospective 90 85
Number known MRI Gadolinium Pulse- Angiography Analysis
2003
Year Nagel
Author Ref. of 84
12
no Rest/Stress
Perfusion 0.025
Dose SR-GRE-EPI ≥75 retrospective 88
Sensitivity 90
Specificity
Pts. CAD Sequence (CAD Method2
excluded Protocol1 (mmol/kg) definition)
2003 Doyle 13
138 no Rest/Stress 0.04 SR-GRE ≥70 prospective3 57 85
2004 Wolff 14
75 no Stress/Rest 0.05-0.15 SR-GRE-EPI ≥70 prospective5 93 75
2004 Giang 15
80 no Stress 0.05-0.15 SR-GRE-EPI ≥50 retrospective 5
93 75
2004 Paetsch 16
79 no Stress/Rest 0.05 SR-GRE-EPI >50 prospective 91 62
2004 Thiele 17
20 no Rest/Stress 0.05 SR-GRE 6
≥70 retrospective 75 97
2004 Plein 18
68 no 4
Rest/Stress 0.05 SR-GRE 6
≥70 prospective 88 83

3 2005 Plein 19
92 no Rest/Stress 0.05 SR-GRE6 >70 retrospective 88 82
2005 Sakuma 20
40 yes Rest/Stress 0.03 SR-GRE ≥70 prospective 81 68
2006 Klem 21
92 yes Stress/Rest 0.065 SR-GRE 6
≥70 prospective 84 †
58†
2006 Cury Stress Perfusion MRI Studies in Humans With
22
47 no Stress/Rest 0.1 SR-GRE-EPI ≥70 prospective 81*§ 87*§
2006
2006
Rieber
Pilz
Coronary Angiography Comparison (3 of 3)
23

24
43
171
no
no
Stress/Rest
Stress/Rest
0.05
0.1
SR-GRE
SR-GRE-EPI
>50
>70
retrospective
prospective
88
96
90
83
2007 Greenwood 25
35 Ptsnowith
4
Rest/Stress 0.05 SR-GRE6 ≥70
X-Ray prospective 86‡ 100‡
Number known MRI Gadolinium Pulse- Angiography Analysis
2007
Year Cheng
Author Ref. of 61
26
no Stress/Rest
Perfusion 0.04
Dose SR-GRE6 ≥50 prospective 90
Sensitivity 67
Specificity
Pts. CAD Sequence (CAD Method2
excluded Protocol1 (mmol/kg) definition)
2007 Costa 27
30 no Stress/Rest 0.1 SR-GRE ≥50 retrospective 85* 39*
2008 Burgstahler 28
20 yes7 Stress/Rest 0.1 SR-SSFP6 >70 prospective 100 80
2008 Klein 29
54 yes Stress/Rest 0.05 SR-SSFP >50 prospective 87 88

2008 Doesch 30
141 no Stress/Rest 0.1 SR-GRE6 ≥75 prospective 90‡ 77‡
2008 Schwitter 31
2348 no Stress/Rest 0.18 SR-GRE ≥50 prospective 85 67

2008 Klem 32
80 yes Stress/Rest 0.07 SR-GRE ≥70 prospective 86‡ 91‡

2008 Kitagawa 33
50 no Stress/Rest 0.05 SR-SSFP ≥50 prospective 86#‡ 75#‡
2009 Bernhardt 34
823 no Stress 0.1 SR-GRE-EPI/-SSFP ≥70 prospective 89||‡ 81||‡

Total 34 2,880

Average 85 81

3.6.14 Chapter 3: Patient Assessment

Table 3
Stress Perfusion MRI Studies in Humans With Coronary Angiography Comparison

CAD = coronary artery disease; 3

Pilot study performed first to determine the best †Sensitivity/specificity after incorporating DE-MRI
DE-MRI = delayed enhancement magnetic threshold for test abnormality. were 89% and 87%, respectively.
resonance imaging; 4
At enrollment, all patients had the clinical §Sensitivity/specificity after incorporating DE-MRI
EPI = echo-planar imaging;
diagnosis of ST elevation, non-ST elevation were 87% and 89%, respectively.
GRE = gradient-recalled echo;
myocardial infarction, or acute coronary syndrome.
IR = inversion recovery prepulse; MRI, magnetic #Represents average values of the two observers;
resonance imaging;
5
Reported sensitivity and specificity are from a average sensitivity/specificity after incorporating
SR = saturation recovery prepulse; fraction of the total cohort, a subgroup with the DE-MRI were 92% and 54%, respectively.
SSFP = steady-state free precession; best results.
||Represents average sensitivity/specificity of the
NS = not stated.*Numbers based on a regional 6
With parallel imaging acceleration. entire study population after incorporating DE-MRI
rather than per-patient analysis. (algorithm A).
All patients had relevant aortic stenosis.
7
1
When both rest and stress imaging were ‡DE-MRI was incorporated in image analysis.
8
Multicenter trial with five different contrast
performed, the order is as listed.
doses; the sensitivity/specificity are estimates from
2
Prospective studies were those in which the receiver operating characteristic analysis, which
criteria for test abnormality were prespecified is based on the results from the group with the
before data analysis. optimum contrast dose (n = 45).

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Magn Reson Imaging 2001;14:556-62. WISE study. J Cardiovasc Magn Reson detection of coronary artery disease by
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6. Schwitter J, Nanz D, Kneifel S, et al.
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Assessment of myocardial perfusion 14. Wolff SD, Schwitter J, Coulden R, et al.
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3.6: Cardiovascular Magnetic Resonance Imaging 3.6.15

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24. Pilz G, Bernhardt P, Klos M, Ali E, Wild M, 28. Burgstahler C, Kunze M, Gawaz MP, et 32. Klem I, Greulich S, Heitner JF, et al. Value
Hofling B. Clinical implication of adenosine- al. Adenosine stress first pass perfusion of cardiovascular magnetic resonance
stress cardiac magnetic resonance imaging for the detection of coronary artery stress perfusion testing for the detection
as potential gatekeeper prior to invasive disease in patients with aortic stenosis: a of coronary artery disease in women. JACC
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25. Greenwood JP, Younger JF, Ridgway JP, Combined magnetic resonance coronary perfusion MRI and late gadolinium-
Sivananthan MU, Ball SG, Plein S. Safety artery imaging, myocardial perfusion and enhanced MRI for detecting flow-limiting
and diagnostic accuracy of stress cardiac late gadolinium enhancement in patients coronary artery disease: a multicenter
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26. Cheng AS, Pegg TJ, Karamitsos TD, et resonance imaging for the assessment of enhancement in patients after
al. Cardiovascular magnetic resonance ischemic heart disease. Clin Res Cardiol percutaneous coronary intervention or
perfusion imaging at 3-tesla for the 2008;97:905-12. bypass grafts: a multicenter study of
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31. Schwitter J, Wacker CM, van Rossum AC, et
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27. Costa MA, Shoemaker S, Futamatsu H, photon emission computed tomography
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quantitative approach (i.e., regions of interest are drawn on terms of scanner hardware (DE-MRI images can be built up over
the images and image intensities are measured) for diagnostic several seconds rather than in 0.1 second, as is required for first-
assessment. pass perfusion).78 Thus, DE-MRI should be more accurate for the
diagnosis of MI.78
Although a quantitative approach has the potential advan-
tage of allowing the measurement of absolute blood flow, the Conceptually, it then follows that perfusion defects that
approach requires extensive interactive post-processing and is have similar intensity and extent during both stress and rest
time-consuming. As a result, a quantitative approach has not (“matched defect”), but do not have infarction on DE-MRI,
3 been feasible for general clinical use and is uncommonly utilized are artifactual and should not be considered positive for CAD.
outside of the research setting. Conversely, the presence of infarction on DE-MRI favors the
diagnosis of CAD, even if the results of perfusion imaging are
In contrast, image interpretation by simple visual assessment equivocal.
would be a realistic approach for a clinical CMR practice. Unfor-
tunately, the results in the literature regarding visual assessment This multi-component approach to image interpretation has
of perfusion MRI are mixed, generally demonstrating adequate been studied in a variety of patient cohorts, including those
sensitivity but relatively poor specificity for the detection of at intermediate risk for CAD,75,79 with known or suspected
CAD. In large part, image artifacts are responsible for reduced CAD,80,81 with history of revascularization,82 and undergoing
specificity. However, there is no reason to interpret the stress risk stratification after successful thrombolytic therapy for ST-
perfusion images in isolation. segment elevation MI.83 Although direct head-to-head data are
lacking, these studies suggest that rapid visual assessment using
The “core” exam is a multi-component protocol that includes this combination protocol provides results that are comparable
cine- and DE-MRI in addition to stress and rest perfusion. In to, if not better than, competing technologies. As a result, many
this context, it is noteworthy that an interpretation algorithm clinical laboratories have adopted this methodology.
that combines data from perfusion MRI and DE-MRI has been
introduced, which substantially improves the specificity and Viability and Infarction
accuracy of rapid visual assessment for the detection of CAD Although a variety of MRI techniques have been utilized to
(Figure 12).75 assess myocardial viability, currently, only dobutamine cine-MRI
and DE-MRI are used clinically. In general, DE-MRI is preferred
The algorithm is based on two simple principles. First, with over dobutamine cine-MRI because DE-MRI may be performed
perfusion MRI and DE-MRI, there are two independent methods without the use of inotropic agents or special monitoring
to obtain information regarding the presence or absence of MI. equipment.84 Not surprisingly, the vast majority of clinical sites
Thus, one method could be used to confirm the results of the perform DE-MRI rather than dobutamine cine-MRI for viability
other. Second, DE-MRI image quality (e.g., signal-to-noise ratio) assessment; thus, the following discussion will focus on DE-MRI.
is far better than perfusion MRI because it is less demanding in

3.6.16 Chapter 3: Patient Assessment

Figure 12
Interpretation Algorithm for Incorporating DE-MRI With Stress and Rest Perfusion MRI for the Detection of CAD
(A) Schema of the interpretation algorithm. (1) Positive delayed-enhancement magnetic resonance imaging (DE-MRI) study. Hyperenhanced myocardium
3
consistent with a prior myocardial infarction (MI) is detected. Does not include isolated midwall or epicardial hyperenhancement, which can occur in
nonischemic disorders. (2) Standard negative stress study. No evidence of prior MI or inducible perfusion defects. (3) Standard positive stress study: No
evidence of prior MI, but perfusion defects are present with adenosine that are absent or reduced at rest. (4) Artifactual perfusion defect: Matched stress
and rest perfusion defects without evidence of prior MI on DE-MRI.
(B) Patient examples. Top row: Patient with a positive DE-MRI study demonstrating an infarct in the inferolateral wall (red arrow), although perfusion-MRI
is negative. The interpretation algorithm (step 1) classified this patient as positive for coronary artery disease (CAD). Coronary angiography verified disease
in a circumflex marginal artery. Cine-MRI demonstrated normal contractility. Middle row: Patient with a negative DE-MRI study, but with a prominent
reversible defect in the anteroseptal wall on perfusion-MRI (red arrow). The interpretation algorithm (step 3) classified this patient as positive for CAD.
Coronary angiography demonstrated a proximal 95% left anterior descending artery stenosis. Bottom row: Patient with a matched stress-rest perfusion
defect (blue arrows), but without evidence of prior MI on DE-MRI. The interpretation algorithm (step 4) classified the perfusion defects as artifactual.
Coronary angiography demonstrated normal coronary arteries.
Reproduced with permission from Klem I, Heitner JF, Shah DJ, et al. Improved detection of coronary artery disease by stress perfusion cardiovascular
magnetic resonance with the use of delayed enhancement infarction imaging. J Am Coll Cardiol 2006;47:1630-8.

Validation Studies DE-MRI images in patients with large and small MIs are shown
There is an abundance of validation data in animal models in in Figure 14. DE-MRI provides scar size measurements that are
which DE-MRI has been directly compared to the histopathol- closely correlated with positron emission tomography (PET) in
ogy.22,23,32 These data demonstrate a nearly exact relationship be- patients with ischemic cardiomyopathy85 and also provides results
tween the size and shape of infarcted myocardium by DE-MRI to superior to (SPECT) in patients with subendocardial infarctions.25
that by histopathology (Figure 13). Human studies demonstrate
that DE-MRI is effective in identifying the presence, location, and Recently, DE-MRI was evaluated in an international multicenter
extent of MI in both the acute and chronic settings.24,26 Typical trial for the detection of MI.86 In total, 282 patients with acute
and 284 with first-time MI were scanned in 26 centers through-

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.17

 Figure 13
Comparison of Ex-Vivo,
High-Resolution Delayed-Enhancement
MR Images With Acute Myocardial
Necrosis
Comparison of ex-vivo, high-resolution delayed-
enhancement magnetic resonance (MR)
images with acute myocardial necrosis defined
histologically by triphenyltetrazolium chloride
(TTC) staining. Note that the size and shape of
the infarcted region (yellowish-white region)
defined histologically by TTC staining is nearly
exactly matched by the size and shape of the
hyperenhanced (bright) region on the delayed
enhancement image.
Modified with permission from Kim RJ, Fieno
DS, Parrish TB, et al. Relationship of MRI delayed
contrast enhancement to irreversible injury,
infarct age, and contractile function. Circulation
1999;100:1992-2002.

out the United States, Europe, and South America. The study Assessing Viability
demonstrated that the sensitivity of DE-MRI increased with A straightforward clinical application of DE-MRI is to differen-
rising gadolinium dose, reaching 99% and 94% in acute and tiate patients with potentially reversible ventricular dysfunc-
3 chronic MI, respectively, with the 0.3 mmol/kg dose (Figure 15). tion from those with irreversible dysfunction. In the setting of
Furthermore, with doses 0.2 mmol/kg or higher, when MI was ischemic heart disease, it is primarily the former group that will
identified, it was in the correct location in more than 97% of benefit from coronary revascularization. The use of DE-MRI for
patients (i.e., the location of hyperenhancement matched the this purpose is further discussed in the module on Hibernation,
perfusion territory of the infarct-related artery). Stunning/Viability in Chapter 7.

Importantly, this study represents the first multicenter trial Heart Failure and Cardiomyopathies
designed to evaluate an imaging approach for detecting MI. In patients with heart failure, it is important to determine the
Although multicenter trials have used infarct size measurements etiology of heart failure in order to appropriately plan therapy
by SPECT as a surrogate endpoint to assess the efficacy of an and provide prognostic information.88 Even in asymptomatic
investigative therapy,87 these trials were not designed to evalu- patients in whom systolic dysfunction is not yet evident, early
ate SPECT, and limited multicenter data on the sensitivity or diagnosis may allow preventive measures that can change the
accuracy of radionuclide imaging for detecting or localizing MI natural history of the disease and can trigger family screening
have been reported. procedures in genetic disorders. Unfortunately, the etiology
of cardiomyopathy is often difficult to ascertain, and standard
In addition, the DE-MRI trial tested the sensitivity of imaging for noninvasive imaging may not be definitive.
both acute and chronic MI. This is notable because there are far
less clinical trial data on the detection of chronic MI by imag- DE-MRI is useful not only for detecting acute and chronic MI,
ing methods, and chronic infarcts are generally more difficult and for predicting functional improvement after revasculariza-
to detect than acute infarcts because substantial shrinkage can tion but also for characterizing an extensive array of cardiomy-
occur during healing.23 Thus, in summary, the data indicate that opathies. The utility of DE-MRI in the setting of cardiomyopathy
DE-MRI is a well-validated, robust technique that can be easily is based on the understanding that rather than simply measur-
implemented on scanners that are commonly available world- ing viability, the presence and pattern of hyperenhancement
wide with an effectiveness that rivals the best available imaging holds additional information.
techniques for the detection and assessment of MI.

3.6.18 Chapter 3: Patient Assessment

 Figure 14
Representative DE-MRI
Images in Patients With
Chronic Myocardial
Infarction
Both large (top row) and small
(bottom row) infarcts are shown.
DE-MRI = delayed-enhancement
magnetic resonance imaging.
Modified with permission
from Wu E, Judd RM, Vargas
JD, Klocke FJ, Bonow RO, Kim
RJ. Visualisation of presence,
location, and transmural extent
of healed Q-wave and non-
Q-wave myocardial infarction.
Lancet 2001;357:21-8.

Recently, a systematic approach to interpreting DE-MRI images hancement patterns that may be encountered in clinical practice
in patients with heart failure or cardiomyopathy has been pro- along with a partial list of their differential diagnoses.
posed.89,90 This approach is based on the following three steps:
Pericardial Disease and Cardiac Masses
Step 1: The presence or absence of hyperenhancement is deter- Constrictive Pericarditis
mined. In the subset of patients with longstanding severe isch- Currently, pericardial constriction is best assessed using a combi-
emic cardiomyopathy, the data indicate that virtually all patients nation of turbo-spin echo93 morphology and SSFP cine imaging 3
have prior MI.91 The implication is that in patients with severe (Figure 18). In addition to conventional cine imaging, tagged
cardiomyopathy but without hyperenhancement, the diagnosis of cine-MRI and real-time cine-MRI may provide supplementary
idiopathic dilated cardiomyopathy should be strongly considered. information. With cardiac tagging, discrete tissue points can be
tracked throughout the cardiac cycle. This is accomplished using
Step 2: If hyperenhancement is present, the location and dis- RF prepulses to label tissue (usually at end-diastole) with a dark
tribution of hyperenhancement should be classified as a CAD grid pattern (Figure 6). Normally, gridlines at the interface be-
or non-CAD pattern. To distinguish these patterns, the concept tween pericardium and epicardium (actually between parietal and
that ischemic injury progresses as a “wavefront” from the sub- visceral pericardium, as the latter is attached to the epicardium)
endocardium to the epicardium is fundamental.92 For example, should shear during systole since the two surfaces move inde-
hyperenhancement patterns that spare the subendocardium pendently and slide during contraction. Conversely, in the setting
and are limited to the middle or epicardial portion of the LV wall of pericardial adhesions, gridlines at the interface should remain
should generally be considered as non-CAD. intact, as motion of the two surfaces would be concordant.

Step 3: If hyperenhancement is present in a non-CAD pattern, Real-time cine-MRI can be used to demonstrate increased ven-
further classification should be considered. There are now tricular interdependence, a hemodynamic hallmark of pericardial
considerable data, which demonstrate that certain nonischemic constriction.94 Specifically, abnormal ventricular septal motion
cardiomyopathies have predilection for specific scar patterns. toward the LV in early diastole is seen during the onset of in-
For instance, in the setting of LV hypertrophy, the presence of spiration (Figure 18). Although the number of patients studied
midwall hyperenhancement in one or both junctions of the is quite small, this finding appears helpful in distinguishing be-
interventricular septum and RV free wall is highly suggestive tween constrictive pericarditis and restrictive cardiomyopathy.94
of hypertrophic cardiomyopathy, whereas midwall or epicar-
dial hyperenhancement in the inferolateral wall is consistent Masses
with Anderson-Fabry disease. Moreover, instead of an infinite A large body of literature addresses the utility of CMR for the
variety of hyperenhancement patterns, it appears that a broad evaluation of cardiac masses. Much of this literature concerns
stratification is possible in a limited number of common DE-MRI attempts to characterize different tissues by comparing image
phenotypes. Figures 16 and 17 illustrate potential hyperen- intensities on T1- T2-, and proton-density weighted images.

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.19

 Figure 15
Sensitivity of DE-MRI
Sensitivity of DE-MRI for Acute and Chronic Myocardial Infarction
for Acute and Chronic Sensitivity (%)
Myocardial Infarction
99 99
The diagnostic sensitivity of
Acute MI (n = 282) 95
(97-100) 92 (98-100)
100 84
(90-100) (86-98)
detecting myocardial infarction (76-93) 80
(70-89)
(MI) is summarized according 80
to gadoversetamide dose
60 48 45
group and imaging time point. (36-59) (34-56)
Numbers in parentheses are 40
95% confidence intervals. 14 13
17 15
20 (6-22) (8-26) (7-24)
DE-MRI = delayed-enhancement (5-21)

magnetic resonance imaging.

0
Precontrast Post-10 Mins Post-30 Mins
Modified with permission from
Kim RJ, Albert TS, Wible JH,
Chronic MI (n = 284) 94 92
et al. Performance of delayed- 100 87 (89-100) 84 (86-99)
83 (79-95)
enhancement magnetic (74-91) 73
(76-93)

resonance imaging with 80 (62-83)

0.05 0.1 0.2 0.3

gadoversetamide contrast for 60

Dose (mmol/kg)
Gadoversetamide
52
(40-63) 44
the detection and assessment (33-52)
of myocardial infarction: an 40
international, multicenter, 10
20 6 8
double-blinded, randomized (1-22)
3 (2-15) (3-17)
(0-7)
trial. Circulation 2008;117:629- 0
Precontrast Post-10 Mins Post-30 Mins
37.

Figure 16
Hyperenhancement
Patterns That May Be
Encountered in Clinical Hyperenhancement Patterns
3 Practice
That May Be Encountered in Clinical Practice
Since myocardial necrosis due to
coronary artery disease (CAD) CAD Non-CAD
progresses as a “wavefront” A. Subendocardial Infarct A. Mid-wall HE
from the subendocardium to the
epicardium, hyperenhancement
(HE) (if present) should always
involve the subendocardium
in patients with ischemic • Dilated • Hypertrophic Cardiomyopathy • Sarcoidosis
Cardiomyopathy • Right ventricular pressure • Myocarditis
disease. Isolated mid-wall or
• Myocarditis overload (e.g. congenital • Anderson-Fabry
epicardial HE strongly suggests
heart disease, pulmonary HTN)
a “nonischemic” etiology. • Chagas Disease
Additionally, endocardial HE that
B. Epicardial HE
occurs globally (i.e., throughout
the left ventricle) is uncommon B. Transmural Infarct
even with diffuse CAD, and
therefore, a nonischemic
etiology should be considered.
HE = hyperenhancement. • Sarcoidosis, Myocarditis, Anderson-Fabry, Chagas Disease

Reproduced with permission

C. Global Endocardial HE
from Shah DJ, Kim RJ. Magnetic
Resonance of Myocardial
Viability. In: Edelman RR,
Hesselink J, Zlatkin M. Clinical
Magnetic Resonance Imaging. • Amyloidosis, Systemic Sclerosis, Post cardiac transplantation
3rd ed. New York: Elsevier;
2005.

3.6.20 Chapter 3: Patient Assessment

Figure 17
Representative Delayed-Enhancement Images in Patients With Various Nonischemic Cardiomyopathies
The hyperenhancement patterns in all patients are distinctly “non-coronary artery disease” type.
Dilated cardiomyopathy (DCM). Arrows point to a linear stripe of hyperenhancement that is limited to the mid-wall of the interventricular septum.
Hypertrophic cardiomyopathy (HCM). Arrows point to multiple foci of hyperenhancement, which are predominantly mid-myocardial in location and
occur in the hypertrophied septum and not in the lateral left ventricular (LV) free wall. The junctions of the right ventricular free wall and interventricular
septum are commonly involved. 3
Myocarditis. Arrows point to two separate regions of hyperenhancement: a linear mid-wall stripe in the interventricular septum, and a large confluent
region affecting the epicardial half of the LV lateral wall.
Amyloidosis. Arrows point to hyperenhancement affecting the subendocardial half of the myocardial wall diffusely throughout the entire LV.

However, differentiating between benign and malignant masses cysts can be identified by characteristic high image intensity on
by image intensities was usually poor.95 This approach to cardiac SSFP sequences or by DE-MRI in a manner similar to that used to
masses, which relied primarily on older SE sequences, should no detect pericardial fluid. Finally, other morphological characteristics
longer be used in clinical practice. Instead, at present, a typical such as tissue invasion or compression, flow obstruction, and as-
protocol for the evaluation of a cardiac mass should consist of sociated pericardial effusion are imaged by this protocol.
multiple pulse sequences where the aim is to assess morphol-
ogy, motion, perfusion, and delayed enhancement, in addition Left Ventricular Thrombus
to inherent differences in T1 and T2 (Figure 19). This compre- LV thrombus represents an important subset of cardiac masses.
hensive protocol identifies both normal variants often mistaken Although most common in the LV apex, thrombus may occur
for cardiac masses (e.g., eustachian valve, lipomatous septal elsewhere with predilection for locations with stagnant blood
hypertrophy, warfarin ridge) and abnormal physiological charac- flow such as adjacent to akinetic infarcted myocardium. The
teristics of masses, which may point to a specific diagnosis. For presence of LV thrombus may be apparent on cine-MRI, if the
instance, perfusion MRI may demonstrate increased vascularity, thrombus is clearly intracavitary. However, layered mural throm-
which may be prominent in malignancies such as angiosarcoma; bus may be difficult to detect since image intensity differences
DE-MRI may identify areas of tissue necrosis within the core of a between thrombus and myocardium are minimal.96-99
malignant tumor, which appear as areas of hyperenhancement.
Recent studies suggest that DE-MRI following contrast adminis-
Other sequences may also be helpful. Fat can be verified by imag- tration may be an improved method for detecting LV thrombus.
ing first without and then with fat saturation techniques. Simple Mollet et al. reported that DE-MRI identified LV thrombus in

3.6: Cardiovascular Magnetic Resonance Imaging 3.6.21

3 Figure 18
Representative Images From a Patient With Pericardial Constriction
Breath-hold cine-MRI (single phase shown) and T2-weighted turbo-spin echo (TSE) imaging shows marked pericardial thickening (orange arrowheads).
Real-time cine-MRI demonstrates displacement of the interventricular septum (orange arrows) towards the left ventricle during early inspiration, consistent
with ventricular interdependence. The dotted orange line highlights the movement of the diaphragm.

substantially more patients than cine-MRI or transthoracic echo- DE-MRI as a better reference standard than cine-MRI. Interest-
cardiography; however, a reference standard was not available.96 ingly, patients with ischemic cardiomyopathy were more than
Srichai et al. evaluated a protocol combining cine-MRI and DE- 5 times more likely to have thrombus than those with nonisch-
MRI for the diagnosis of LV thrombus in patients with advanced emic cardiomyopathy despite similar mean LVEF. Additionally,
ischemic cardiomyopathy undergoing surgical LV reconstruc- myocardial scarring, also detected by DE-MRI, was identified as
tion.97 Among 160 patients (using a reference standard that a novel risk factor for thrombus. In a second study, Weinsaft et
consisted of direct visualization of the LV cavity during surgery al. showed that even when sonographic contrast is routinely
and/or pathological confirmation), CMR showed higher sensitiv- utilized, echocardiography may fail to identify up to 39% of
ity and specificity (88% and 99%, respectively) than transtho- thrombi detected by DE-MRI.99 Based on these data, DE-MRI
racic (23%, 96%) and transesophageal echocardiography (40%, may represent an emerging “gold standard” for the diagnosis
96%) for the diagnosis of LV thrombus. of LV thrombus.

Weinsaft et al. assessed the prevalence of LV thrombus by cine- Key Points

and DE-MRI in 784 consecutive patients with systolic dysfunc-
tion (LV ejection fraction [EF] <50%).98 Among this broad • CMR has the ability to generate substantial soft tissue
population, DE-MRI detected thrombus in 7% (55 patients) contrast because of differences in tissue T1 and T2
and cine-MRI in 4.7% (37 patients), and clinical follow-up for (inherent or altered by contrast media).
embolic events or pathological confirmation was consistent with

3.6.22 Chapter 3: Patient Assessment

Figure 19
Evaluation of a Cardiac Mass 3
The protocol consists of (a) one or more stacks of single-shot imaging that combines rapid image acquisition with comprehensive anatomic coverage to
quickly delineate morphology; (b) cine imaging to view motion during the cardiac cycle; (c) first-pass perfusion imaging during the transit of an intravenous
bolus of gadolinium contrast; and (d) post-contrast delayed-enhancement magnetic resonance imaging (DE-MRI), which accentuates differences in contrast
uptake between the mass and normal myocardium and between different regions of the mass. In this patient with a left atrial mass (arrows), biopsy
demonstrated recurrent invasive thymoma (note that several extracardiac masses are also present). Perfusion is reduced compared with left ventricular
myocardium. Hyperenhancement is present in a heterogeneous fashion.
Reproduced with permission from Fuster V, Kim RJ. Frontiers in cardiovascular magnetic resonance. Circulation 2005;112:135-44.

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3.6.26 Chapter 3: Patient Assessment