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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5189_Библиотеки_им_академика_М_И_Перельмана.pdf
10 Artifacts andPitfalls inTransesophageal Echocardiography
Fig. 10.2 Descending
aortic short axis with an
example of a mirror
image artifact of the
descending aorta
117
To generate an image, a sound beam is emitted
and travels through tissues. Normally, the sound is
then reected by the structure and travels back to
the probe unaltered and uninterrupted. Some of the
ultrasound beam, however, can be reected by a
second reector (i.e., vessel wall, pericardium). The
beam returns for the second time towards the original reector before reecting back again towards
the probe. The processing software locates this second signal as an object located twice the distance
from the probe because it listened for twice the transit time before receiving the ultrasound beam [4, 5].
Common reectors in clinical echo include
the anterior wall of the aorta, the left atrial–aortic
wall interface, and the pulmonary artery–aortic
interface. The two gures in this section show
two examples of the aortic wall (the rst reector) and the resulting artifact. Mirror artifact can
manifest a whole mirror image below the anatomical aorta resulting in a double barrel aortic
artifact (Fig.10.1) or an artifact aorta below the
real one in cross section (Fig.10.2). Reverberation
artifacts always occur as a reoccurring structures
equidistant from each other below the real object.
generation occurs from excitation of piezoelectric crystals within the probe, which contract and expand as an acoustic wave in the
direction of the probe. The piezoelectric elements also contract and expand radially and
produce secondary beams. These are unwanted
but will be present. These radial beams are
called side-lobe beams and are low-intensity
beams surrounding the central beam. Side-lobe
artifacts occur when enough side lobe hit a
highly reective surface and get interpreted as
returning with the main beam. Figure 10.3
visually demonstrates side-lobe artifact. The
intensity of the side-lobe beams are usually
less than the main beam, so the artifact is often
less echogenic on screen and can be linear or
curvilinear [4, 6].
[There are three things to look for in an
ultrasound image when a side-lobe artifact
is suspected; (1) A strong reector with an
(2) acoustic shadow below it and (3) lateral
displacement of the side-lobe artifact from
the strong reector.]
Side-Lobe Artifact
A side-lobe artifact violates the assumption
that all echoes originate from objects located
on the transducer axis. Typically, ultrasound
118
Side lobesSide
M. Behrens and T. T. Tauh
A
Main beam
C
B
Side lobes: Forming of the
ultrasound beam is associated
with some ultrasound energy
travelling off-axis in so-called
side lobes.
The main beam sweeps through the sector
to obtain the image.
321
The objects is
recoreded by
the main beam.
Fig. 10.3 Part (a) demonstrates how the ultrasound beam
actually forms a focal point, creating a main lobe with
side lobes fanning radially. Part (b) demonstrates how the
The objects is
recoreded by
Grating lobes
Side lobes
The objects is
recoreded by the
second side lobe.
main beam continuously sweeps through the sector during
image acquisition. Part (c) demonstrates how side lobe
artifact is created
Resulting image
shows a side lobe
artifact.
10 Artifacts andPitfalls inTransesophageal Echocardiography
119
Grating artifacts tend to occur at more oblique
angles (90°), more echogenic and are transducer
dependent. Side lobe is another artifact that can
clinically mimic an aortic dissection intimal ap
as seen in Fig.10.4.
Reverberation and side-lobe artifacts at the
ascending aorta are predictable and expected.
Fig. 10.4 Starting at
the midesophageal aortic
valve long axis view, the
echocardiographer has
withdrawn the probe and
is demonstrating the
ascending aorta in a
nonstandard view. A
side-lobe artifact
mimicking a dissection
ap is visualized
Particularly at the pulmonary arterial–aortic
interface or the left atrial–aorta interface. Tips
to identify artifacts and solutions to avoiding
them are summarized in Table10.2.
Table 10.2
1 Optimize spatial resolution by decreasing gain and eld of view
2 Look for strong reectors above the reverberation artifact, this is usually the left atrial-aortic interface or
3 Both reverberation and side-lobe artifacts do not obey anatomical boundaries and can be seen extending
4 Both reverberation and side-lobe artifacts usually have ill-dened borders
5 Use color ow doppler to establish if ow are the same in both lumens. The presence of similar blood ow
6 Aortic dissection intimal aps often oscillate with the cardiac cycle and blood ow whereas a linear artifact
7 Harmonic imaging mode can limit the side lobes threshold and decrease both side-lobe and grating artifacts
8 Change the echocardiographic view to remove the strong reector interface. E.g., move to a trans-gastric
9 Use multiplane imaging with a systematic approach
10 Clinical correlation and pretest probability should be considered if a pathology is suspected
Tips for identifying and overcoming artifacts in the ascending aorta [7]
Optimize temporal resolution by setting the depth to just below the structure of interest
pulmonary artery–aorta interface
beyond the aorta
velocities on both sides of the ap suggests linear artifact rather than dissection
will be relatively xed with respect to the aortic wall
view from mid esophageal
120
M. Behrens and T. T. Tauh
Intravascular Devices
The echocardiographer will encounter a plethora of intravascular devices in the ICU patient.
While not exhaustive this list may include central venous catheters, pulmonary artery catheters, transvenous pacing wires, prosthetic
valves, percutaneous microaxial circulatory
support, extracorporeal membrane oxygenator
(ECMO) cannulas, and intraortic balloon
pumps (IABP).
Identifying the type of devices will be based
on clinical scenario, anatomic location, size, and
structure. It is not uncommon for critical care
patients to have multiple devices in situ. Any of
the listed devices can be linear structures and can
create both acoustic shadowing and artifacts.
Prosthetic valves, since they have a combination of graft and metallic components, produce
acoustic shadowing. This will limit visualization
distal to the prosthesis. One of the artifacts unique
to intravascular devices is the ring down effect.
This artifact is very common from mechanical
prosthetic valves. The mechanism of ringdown
artifact is the same as reverberation artifact. This
time instead of having only a second reected
sound beam, there are multiple re-reected sound
waves each producing an artifact below the
device. An example of reverberation artifact from
a percutaneous microaxial pump can be seen in
Fig.10.5 [8, 9].
3D Ultrasound
The modern transesophageal echocardiography
(TEE) probe is composed of electrically
independent matrix array transducer allowing for
imaging of cardiac structures in either twodimensional (2D) multiplane imaging, “live” or
“real time” imaging in three-dimensional (3D),
or electrocardiogram- gated multi-beat 3D imaging. While a 2D image is acquired via axial
images, 3D images include the addition of
“depth” or the “Z” plane that allows for real-time
volumetric imaging and acquisition of pyramidal
data sets. ECG-gated 3D acquisitions are multiple sub- volumes added together to complete an
entire 3D image (Fig. 10.6). Technological
advances have improved making it a viable
modality in the clinical setting [10, 11].
3D imaging requires high-quality 2D imaging
and is still governed by the same physics and
constraints of ultrasound. Artifacts exist in 3D as
well. The mechanism of artifact creations are
similar between both modalities. Additional artifacts are unique to how 3D images are acquired
and postprocessed.
Fig. 10.5 Midesophageal long axis view of a
percutaneous microaxial
pump with both ring
down and reverberation
artifact
10 Artifacts andPitfalls inTransesophageal Echocardiography
Fig. 10.6 Multi-beat
3D acquisition of an
aortic valve. Appreciate
how each beat, a
sub-volume of the
structure, is acquired
and “stitched” together
to form the entire 3D
volume and nal image
121
Fig. 10.7 Three-dimensional image of the mitral valve from the surgeons view acquired with multi-beat acquisition
showing a complete 3D volume on the left compared with a 3D volume with these linear artifacts called stich artifacts
Stitch Artifact
the patient’s respiratory cycle, or transducer
movement. Stich artifact appears as shifting or
Stitch artifacts, otherwise known as reconstruction artifact, are misalignment of two or more
contiguous sub-volumes created during ECGgated acquisitions in post processing. In acquiring multi-beat 3D images, sequential volumes of
data are acquired with each beat and then
“stitched” together (Fig. 10.7). The misalignments are most commonly secondary to arrythmia, electrocautery, patient movement including
oscillating sliced segments with demarcated
lines due to the improper merging of the pyramidal sub-volumes. In an irregular rhythm, multibeat ECG-gated 3D acquisition is seldom
practical. Reverting back to single-beat 3D
acquisition or 2D multiplane mode are ways to
circumvent this limitation while still taking
advantage of technology afforded on modern
echo probes.
122
M. Behrens and T. T. Tauh
Blurring andBlooming Artifacts
Blurring artifacts occur as a result of side-lobe
ultrasound beams emitting radially, reecting
and being misinterpreted as part of the main
ultrasound beam (Fig. 10.5). The side-lobe
echoes are then “added” onto the central beam
resulting in objects appearing thicker than they
really are and with indistinct and blurring edges.
In 2D imaging, we are able to adjust axial and
lateral resolution, as well as the focus to minimize side-lobe and beam-width artifacts. In 3D
echocardiography, the elevation (Z plane) is xed
and commonly causes this blurring artifact.
Blooming artifacts are when a blurring artifact
occurs secondary to metallic structures interacting with the ultrasound beam (Fig. 10.8).
Decreasing gain will mitigate blurring or blooming artifact at the expense of resolution and
increase risk of dropout artifact.
Dropout andRailroad Artifacts
signals. While increasing gain can reduce the artifact, it can compromise global image sharpness
and worsening blurring or blooming artifact.
Conversely, over gain artifact in 3D echocardiography appear as brown speckles with blood signal
typically obscuring any structure of interest below.
Railroad artifact is created by vascular catheters
or cannulas with large lumens, for example, ECMO
cannulas or pulmonary artery catheters. Similar to
dropout artifact, the sections of the device that
interact with the ultrasound beam at an oblique
angle return weak or without signal (Table10.3).
Dropout artifacts occur most commonly to thin
structures, such as valve leaets or the inter-atrial
septum when imaged in a non-perpendicular orientation (Fig. 10.9). This oblique interrogation
with the ultrasound beam coupled with a poor
reector results in scattering of the ultrasound
beam and suboptimal signals. Dropout artifact
appears as transparent tissues, holes, or perforations on the 3D image due to a paucity of returning
Fig. 10.9 Threedimensional short axis
of the aortic valve with
an example of drop out
artifact at the level of the
aortic leaets
Fig. 10.8 Three-dimensional full volume showing an
example of a blurring artifact from a pulmonary artery
(PA) catheter
10 Artifacts andPitfalls inTransesophageal Echocardiography
123
Table 10.3
Artifact Description Tips
Stitch Reconstruction artifact due to
Blurring and blooming Side-lobe beams adding to the main
Drop-out and railroad Thin structures with oblique angles
Common Anatomical Variants
andPitfalls
Artifacts in three-dimensional (3D) echocardiography
improper merging of multiple beat
sub-volumes
beam inappropriately
The focus is not at the area of
interest
to the ultrasound beam
The eustachian valve is seen in approximately a
quarter of adults as a 1–2cm crescent-shaped thin
• Arrythmia, electrocautery, patient movement
• Respiratory artifact, hold ventilator
• Decrease the number of multi-beats acquired
• If unable to acquire 3D, then trial 2D
• Adjust the focus point to the structure of
• Optimize spatial resolution by decreasing
• Optimize temporal resolution by setting the
• Harmonic imaging mode can limit the side
• Optimize gain to bring in drop-out areas
• Change the viewing window to optimize
band of tissue originating at the posterior junction
Anatomic variants typically are either normal
anatomy or remnants of embryologic gestation
that are misinterpreted for pathology.
Classication of anatomic variants is easiest via
anatomic location. A complete list of common
anatomical variants is organized in Table 10.4.
While a complete list of all the possible variants
is beyond the scope of this chapter, the highest
yield structures both clinically and for examination are discussed below in more detail.
of the inferior vena cava (IVC) and the right atrium,
and extends both anteriorly and superiorly
(Fig.10.11). As a remnant, its purpose was to preferentially direct blood ow towards the patent foramen ovale. The eustachian valve is most commonly
seen near the IVC in the mid- esophageal bicaval
view or the right ventricular inow outow view.
The eustachian valve typically does not directly
cause ow acceleration on color ow doppler.
Rarely, it has been mistaken for thrombus. However,
the eustachian valve can complicate IVC cannulation or be a site for endocarditis or thrombosis [7].
Right Atrium: Crista Terminalis, Eustachian Valve, Chiari Network
Another anatomical variant, the Chiari network, can arise anterior to the orice of the
IVC. This network is a thin lamentous, fenes-
The crista terminalis is located at the junction of
the superior vena cava (SVC) and the right atrium
near the right atrial appendage. Anatomically, it
separates the smooth and trabeculated layers of
the atrial wall. The crista terminalis is typically
seen by the SVC in the mid-esophageal bicaval
view and can be misinterpreted as a tumor or
thrombus (Fig.10.10).
trated, mobile structure and is an embryological
remanent of the sinus venosus (Fig. 10.12). It
commonly originates at the IVC and RA junction;
however, it can originate from other structures
including the right atrium, inter-atrial septum, or
the coronary sinus. Similar to the Eustachian
valve, the Chiari network most commonly arises
from the orice of IVC, but the Chiari network is
worsen artifact
multiplane
interest to minimize wide beam artifact
gain and eld of view
depth to just below the structure of interest
lobe’s threshold and decrease side-lobe and
grating artifacts
while minimizing blurring
reecting angle as close to 90° as possible
124
M. Behrens and T. T. Tauh
Table 10.4
Right atrium Right ventricle Left atrium Left ventricle
Chiari network Moderator
Crista terminalis Left atrial appendage False tendons and LV
Dilate coronary sinus and persistent
SVC
Eustachian valve Transverse sinus
Fossa ovalis
Interatrial septum aneurysm
Lipomatous interatrial septum
Right atrial appendage
Thebesian valve
Trabeculations and pectinate
muscles
Fig. 10.10 Crista
terminalis is labeled in a
modied bicaval view
Common anatomic variants grouped by anatomical location
Coumadin ridge Calcied chordae
band
Trabeculations and pectinate
muscles
tendineae
bands
Lambl’s excrescence
thinner and more mobile. In echocardiography,
the Chiari network may be mistaken for tricuspid
vegetation, ail tricuspid valve, free RA thrombus, and tumors. Thorough investigation can trace
its attachment most commonly to the IVC and
rarely the interatrial septum and coronary sinus.
Right Ventricle-Moderator Band
The moderator band is a prominent myocardial
trabeculation seen in the mid to apical right ventricle and can be found in much of the population.
Functionally, it is involved in the cardiac conduc-
tion system. The moderator band is commonly
seen in the mid-esophageal four chamber view.
To distinguish it from tumor, thrombus, or catheter, the band is a hyperechoic linear structure on
ultrasound that originates on either wall of the
right ventricle (Fig.10.13).
Left Ventricle: Fibroelastoma Versus Lambl’s Excrescence
Lambl’s excrescence are thin structures typically arising from the aortic valve leaet tips.
Historically, there has been a thought that they
10 Artifacts andPitfalls inTransesophageal Echocardiography
develop from repeated shear forces on the heart
valves at the lines of closure. It has also been
suggested that Lambl’s excrescence could be a
variant of papillary broelastoma. A papillary
broelastoma is pedunculated, speckled pattern, independent in its motion and is associated with either side of the valve surface.
Lambl’s excrescence is more liform, moves
with undulating motion and has the highest
density at valve leaet tips (Fig.10.14). Lambl’s
excrescence have very rarely been associated
with ischemic stroke, making surgical removal
of incidentally found Lambl’s excrescence
quite controversial. Lambl’s excrescence are
best seen in the midesophageal aortic valve
long-axis view [7].
Fig. 10.11 Midesophageal bicaval view with an example
of an eustachian valve (labeled with white arrow) at the
inferior vena cava (IVC) and right atrial (RA) junction
(black arrow). Appreciate how the eustachian valve would
direct blood through the foramen ovale of the intra-atrial
septum (IAS). LA left atrium
125
Fig. 10.12 Chiari network shown in two different views at the inferior vena cava (IVC) and right atrial (RA) junction
126
Fig. 10.13 Midesophageal four
chamber demonstrating
an example of the
moderator band
Fig. 10.14 A zoomed in midesophageal aortic valve
long-axis view with a Lambl’s excrescence, labeled with a
white arrow. RCA right coronary artery
Summary Points
• Ultrasound images are generated by receiving
reecting echoes and by the machine utilizing
certain assumptions, see Table10.1. After post
processing creates an image.
M. Behrens and T. T. Tauh
• Artifacts occur for three reasons: the violation
of ultrasound imaging assumptions, equipment
malfunction, and interactions within an external device.
• Artifacts do not obey anatomical boundaries.
• Artifacts usually need a strong reector. In
TEE, this reector is usually the left atrial–
aortic interface, the pulmonary artery–aortic
interface, or an intravascular device.
• Interrogating the structure of interest from an
alternative view or multiplane imaging will
clinically help avoid erroneous classication
as pathology versus artifact.
• The pretest probability and clinical correlation
of an aortic dissection should be made and
care should be taken to rule out an artifact on
TEE mimicking an aortic intimal ap.
• 3D echo also has artifacts including stich,
blurring, blooming, and those seen in 2D echo
cardiography.
• There are many anatomical variants that
should not be mistaken for artifacts or
pathology.