Cardiac Ultrasound Artifacts
Juan-Carlos Brenes
Craig R. Asher
1. Which of the following fundamental principles of echocardiography is assumed to be correct when interpreting an ultrasound image?
A. All reflections are received from each pulse after the next pulse is sent.
B. The distance to the reflecting object is inversely proportional to the round-trip travel time.
C. The sound emitted by the transducer travels in straight lines.
D. Sound travels in tissue at a speed of 900 m/s.
View Answer
1. Answer: C. The only statement that is correct regarding the fundamentals of echocardiography is that sound travels in a straight line. The other statements are incorrect. Echocardiography is based on the physical principles of sound, which travels through a medium in the form of a propagating wave. There are several assumptions of ultrasound imaging that apply to echocardiography, and the violation of any of these can result in an artifact (Tables 2-1 and 2-2). Artifacts are images that are either not real, located in the wrong place, have an inappropriate brightness, shape, size, or represent structures that are missing.
The ultrasonic wave emitted by the ultrasound probe travels along a straight-line path to and from the transducer. All the echoes that are detected along that straight line originate from the axis of the main beam only. All reflections are received from each pulse before the next pulse is sent. Sound travels in tissue at a speed of 1,540 m/s. The distance to the reflecting object is determined by the elapsed time between the transmitted pulse and the detected echo. This distance is proportional to the round-trip travel time. The amplitude of returning echoes is related directly to the reflecting or scattering properties of distant objects.
2. Which of the following statements regarding the Starr-Edwards mechanical valve (ball and cage) is correct?
A. The speed of sound in the silastic ball is faster than the speed of sound in tissue so that the shape of the ball appears distorted.
B. The speed of sound in the silastic ball is slower than the speed of sound in tissue so that the shape of the ball appears distorted.
C. Ball and cage valves cause a resolution-type artifact.
D. The propagation speed of ultrasound in tissue is assumed to be 13 microseconds to a depth of 1 mm.
View Answer
2. Answer: B. The speed of ultrasound in the silastic ball is slower than the speed of sound in tissue so the shape of the ball appears distorted. One of the basic assumptions of ultrasound is that the speed of ultrasound in tissue is 1,540 m/s (or 13 microseconds/cm). However, different tissues (air, fat, bone), depending on their density and stiffness properties, may speed up or slow down the velocity of ultrasound. The silastic ball of a ball-cage valve (Starr-Edwards valve) slows the velocity of ultrasound. This has the effect of distorting the appearance of the ball from a round to a more oval shape instead of affecting the depth of the ball. This type of artifact is referred to as a propagation speed error artifact not a resolution-type artifact. When the velocity of ultrasound in tissue is slower than expected by the ultrasound machine, the object imaged will be assumed to be farther than it truly is from the transducer. In contrast, when the velocity of ultrasound in tissue is faster than expected by the ultrasound machine, the object imaged will be assumed to be closer than it truly is from the transducer (Fig. 2-13).
Table 2-1. Assumptions of Ultrasound and Artifacts That Occur with Violation | ||||||||||||
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Table 2-2. Common Imaging Artifacts in Two-Dimensional Echocardiography | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 Figure 2-13 |
3. Which of the following statements regarding the development of ascending aorta artifacts during transesophageal echocardiography (TEE) is correct?
A. Linear artifacts within the ascending aorta are most commonly caused by ultrasound refraction.
B. Artifacts are more likely to appear when the aortic diameter is smaller than the left atrial diameter.
C. A linear structure located at half the distance from the transducer as from the anterior aortic wall is most likely an artifact.
D. M-mode echocardiography has proven to be useful in distinguishing artifacts from true aortic flaps.
View Answer
3. Answer: D. M-mode echocardiography remains a useful tool to distinguish ascending aortic artifacts from intimal flaps. There is in vivo and in vitro evidence to support that linear artifacts within the ascending aorta are caused by ultrasound reverberation. In their classic experiment, Appelbe and collaborators introduced an ultrasound probe in a water tank containing two balloons placed in series: a posterior “left atrial balloon” closest to the probe and an anterior “aortic balloon.” They observed that a linear image was consistently present within the aortic balloon when its diameter exceeded the diameter of the left atrial balloon, and since these contained only water, the image was by definition an artifact.
Clinically, it is essential to be able to distinguish artifacts from an intimal flap associated with an aortic dissection. The utilization of criteria to define artifacts in this scenario has been shown to improve the specificity of transesophageal echocardiography (TEE) for the diagnosis of aortic dissection. Artifacts are more likely to appear when the aortic diameter exceeds the left atrial diameter. When applying color Doppler, artifacts usually do not produce turbulence or interruption in the pattern of blood flow as would be seen with the presence of a true and false lumen.
Evangelista et al. described the utility of M-mode applied during TEE in recognizing artifacts as they evaluated 132 patients with suspected aortic dissection. They distinguished several types of artifacts in the ascending aorta. The most common of which were type A and B artifacts. A type A artifact within the ascending aorta was defined as that located twice as far from the transducer as from the posterior aortic wall as shown in Figure 2-14A (AA, ascending aorta; LA, left atrium; T, transducer). By using M-mode echocardiography, they were able to show that intimal flaps have independent motion to the posterior aortic wall and that artifacts usually move parallel to the posterior aortic wall and therefore do not have independent motion. Artifacts also lack rapid oscillatory movements, which are usually associated with intimal flaps.
 Figure 2-14A |
 Figure 2-14B |
Answer A is incorrect since these linear artifacts in the aorta are caused by reverberation, not refraction. Answer B is incorrect since aortic artifacts in the aorta more typically occur when the aortic diameter is larger, not smaller, than the left atrial diameter. Answer C is incorrect since artifacts are usually created at the posterior aortic wall interface with the left atrium not the anterior aortic wall.
A type B artifact is located at twice the distance from the right pulmonary artery posterior wall as from the posterior aortic wall (Fig. 2-14B) (AA, ascending aorta; RPA, right pulmonary artery).
4. Which of the following statements regarding reverberation-type artifacts is correct?
A. They result from repeated reflections off the transducer or other strong reflectors.
B. Reverberation lines are equally spaced located perpendicular to the main axis of the sound beam.
C. Reverberation lines increase in intensity as the distance from the transducer increases.
D. Reverberations occur when the acoustic impedance of two media through which sound is passing is similar.
View Answer
4. Answer: A. Reverberation-type artifacts occur because of multiple reflections off the transducer or strong reflectors. When a strongly reflected echo created at an interface returns to the transducer, some of its energy is redirected back into the patient and it can be reflected again at the same interface. This second echo returns to the transducer at a later time, and the image will be displayed farther away from the real structure since it is assumed to have arisen from a greater depth. Multiple reflections may occur when several interfaces are present for reflection, such as is the case of a mechanical valve disc. The intensity of reverberation lines decreases as the distance from the transducer increases. The reverberation lines are equally spaced and parallel to the main sound beam. Refraction artifacts, not reverberation artifacts, are affected by the difference in acoustic impedance between two media. Figure 2-15 shows two examples of how reverberation artifacts are created (L, returned pulse; R, reflected pulse; T, transmitted pulse).
 Figure 2-15 |
5. Which of the following statements regarding comet tail artifacts is most accurate?
A. They resemble reverberation artifacts with equidistant spaced lines of decreasing intensity associated with increased depth.
B. They violate the straight beam assumption of ultrasound.
C. Common causes of comet tail artifacts include mechanical valves.
D. They cause hypoechoic artifacts that are located parallel to the sound beam.
View Answer
5. Answer: C. Common causes of comet tail artifacts include mechanical valves. Comet-tail artifacts occur when there are highly reflective objects and can occur with various metallic objects but also occur without prosthetic materials. This results in a reverberation-type artifact where there is ringing of the transducer to create a solid hyperechoic beam of ultrasound distal to the object. The creation of a comet tail artifact is similar to reverberation artifacts though the appearance differs in that the comet tail does not have equidistant spaced lines of decreasing intensity (Fig. 2-16, see the arrow). The artifact is located parallel to the sound’s beam and is a violation of time of flight and speed of sound assumptions.
 Figure 2-16 |
6. Which of the following statements regarding the development of beam width artifacts is correct?
A. They occur at the focal zone where lateral resolution is least optimal.
B. They occur distal to the focal zone where lateral resolution is least optimal.
C. Focusing can increase the chance of development of beam width artifacts.
D. They cannot be avoided by adjustments in instrumentation.
View Answer
6. Answer: B. Beam width artifacts occur distal to the focal zone where lateral resolution is least optimal. Two types of beam width artifact may occur: (1) related to slice thickness with superimposition of images from different planes and (2) related to suboptimal lateral resolution distal to the focal zone of the beam. The ultrasound beam has a near field (proximal area to the transducer), focal zone, and far field (distal area to the transducer). In the focal zone, the beam width of the ultrasound reaches its minimum diameter. In the far zone, the beam width becomes wider, and the lateral resolution degrades (lateral resolution diminishes as the depth increases). When the lateral resolution is reduced, a beam width-type of artifact can appear, leading to an alteration in the size or shape of a structure. For example, struts on a prosthetic valve can look longer than the actual size—similar to a side lobe type artifact. The ultrasound beam is two-dimensional and sometimes may superimpose out-of-plane images. An example is the superimposition of shadows from the aorta or aortic valve in the right atrium in an apical 4-chamber view. Focusing (adjustment of the focal zone of the beam) narrows the beam width and the lateral resolution improves, hence reducing the possibility of developing a beam width artifact. Figure 2-17 shows on the left panel that two far-field objects are superimposed on the screen display. On the right panel, the focal zone is adjusted allowing for adequate spatial resolution to distinguish each object separately.
7. Which of the following statements regarding Snell’s law is most accurate?
A. It is the principle that explains the physics of reverberation artifacts.
B. It requires information on the angle of incidence and transmit frequency of the transducer.
C. It requires information on the speed of propagation of ultrasound in two different media and the transmit frequency of the transducer.
D. It requires information on the angle of incidence of the ultrasound beam and speed of propagation of ultrasound in two different media.
View Answer
7. Answer: D. Snell’s law describes the principle by which refraction of ultrasound occurs and contributes to the development of refraction-type artifacts. It requires information on the angle of incidence of the ultrasound beam and speed of propagation of ultrasound in two different media. Under normal conditions if the speed of ultrasound is the same in two media, the transmission angle will equal the incident angle. However, if the speed of ultrasound is greater or less in one media relative to another, the transmission angle will be greater or less than the incident angle and refraction will occur. In other words, refraction refers to the bending of an ultrasound wave as it passes from one media to another and requires different speeds of ultrasound and an oblique angle of incidence to occur.
 Figure 2-17 |
8. Which of the following statements regarding side lobe artifacts is correct?
A. Side lobe artifacts are generated by a weakly reflective object that is close to the central beam of ultrasound.
B. In a side lobe artifact, an image will appear at the wrong location, lateral to the true object location.
C. Side lobe artifacts are created after echoes are returned from highly reflective objects located within the pathway of the central beam.
D. All the energy emitted from an ultrasound transducer remains within the central (main) beam.
View Answer
8. Answer: B. In a side lobe artifact, an image will appear at the wrong location, lateral to the true object location. Most of the energy emitted by the ultrasound machine is concentrated along a central beam. However, not all the energy remains within this central beam. Some of the energy of a mechanical array transducer is also directed to the sides of the central beam (side lobes) that can produce echoes that will return to the transducer particularly if a strong reflector is encountered. The machine assumes that these echoes originate from points along the central beam axis, and the image will be displayed within this central beam. In a side lobe artifact, an image will appear in the wrong location because it places a second echo added laterally to an object seen by the central beam. In Figure 2-18, the top panel shows the ultrasound beam with the central beam (red) and side lobes (gray). The side lobes detect reflectors (gray object) as the transducer rotates side to side and superimposes them on the screen display aside the black object detected by the central beam.
 Figure 2-18 |
9. Which of the following statements regarding refraction type of artifacts is correct?
A. Refraction artifacts develop when the ultrasound beam is completely reflected.
B. Refraction artifacts violate the assumption of ultrasound that all reflections return from a narrow transmit beam.
C. Refraction can cause the appearance of a doubleimage (side-by-side) artifact.
D. Refraction makes structures appear closer to the transducer than they actually are.
View Answer
9. Answer: C. Refraction is produced when the transmitted ultrasound beam is deviated from its straight path line (change in the angle of incidence) as it crosses the boundary between two media with different propagation velocities. In other words, the sound beam bends and causes and artifact displaying a “duplicated” structure. The refracted beam is reflected back to the transducer, leading to an image being displayed in the wrong location. In essence, refraction leads to the lateral displacement of structures from their correct location. Refraction artifacts violate the assumption that ultrasound travels in a straight line and that all pulses are received from a central beam. See Figure 2-19A (L, returned pulse; L′, returned refracted pulse; T, transmitted pulse; T′, transmitted and refracted pulse) and Figure 2-19B (subcostal 4-chamber view; solid white arrows point to right atrial and ventricular walls; dashed white arrows point to the refracted, “duplicated” right atrial and right ventricular wall).
 Figure 2-19A |
 Figure 2-19B |
10. Which of the following statements regarding range ambiguity is true?
A. Range ambiguity occurs when echoes from deep structures created by a first pulse arrive at the transducer before the second pulse has been emitted.
B. Range ambiguity occurs when echoes from deep structures created by a first pulse arrive at the transducer after the second pulse has been emitted.
C. The pulse repetition frequency (PRF) is not affected by the imaging depth.
D. To avoid range ambiguity, PRF is increased when scanning deeper structures.
View Answer
10. Answer: B. Range ambiguity occurs when echoes from deep structures created by a first pulse arrive at the transducer after the second pulse has been emitted. The correct imaging of deep structures is determined by the pulse repetition frequency (PRF). PRF is related to the depth of view. As imaging depth increases, PRF decreases. To avoid range ambiguity, the PRF is reduced when scanning deeper structures, allowing the impulse to return to the transducer on time before the next pulse is emitted. Range ambiguity can lead to the incorrect placement of structures closer to the transducer than their actual location.
11. Which of the following statements regarding mirror-image artifact in spectral Doppler echocardiography is correct?
A. It usually appears when the Doppler gains are set too low.
B. Symmetric spectral images on the opposite side of the baseline from the true signal are created.
C. The mirror image is usually more intense but otherwise very similar to the true signal.
D. It can be reduced by increasing the power output and better alignment of the Doppler beam with the flow direction.
View Answer
11. Answer B. The mirror-image artifact (also known as crosstalk) in spectral Doppler echocardiography appears as a symmetric signal of usually less intensity than the true flow signal on the opposite side of the baseline. The spectral mirror image occurs when the Doppler gains are set too high and it can be reduced by decreasing the power output or gain and optimizing the angle between the ultrasound beam and Doppler flow.
12. Which of the following techniques can help distinguish a left ventricular thrombus from a nearfield clutter artifact?
A. Increasing the depth.
B. Decreasing the transducer frequency.
C. Changing from fundamental to harmonic imaging.
D. Increasing the mechanical index when giving contrast.
View Answer
12. Answer: C. Changing from fundamental to harmonic imaging is helpful in reducing several types of artifacts (side lobes, grating lobes, reverberations, and near-field clutter). Increasing the transducer frequency, decreasing the depth, using multiple views, or the utilization of contrast agents can all help distinguish a left ventricular thrombus from an artifact. Left ventricular thrombus develops almost exclusively in the region of a wall motion abnormality, most commonly seen in an akinetic, dyskinetic, or aneurysmal segment, usually at the apex. Thrombus is usually laminar, with discrete shape and borders, and may appear as protruding or mobile. Its motion is usually concordant with the left ventricular wall. The mechanical index should be decreased when using contrast to avoid excessive destruction of the bubbles. Several structures can mimic a thrombus in the LV (Table 2-3).
Table 2-3. Differential of Structures/Artifacts in the Left Ventricle | ||||
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13. True structures, as opposed to artifacts, are characterized by the following:
A. Ill-defined borders.
B. Visualization in a single view.
C. Not crossing anatomical borders.
D. Lack of attachments to nearby structures.
View Answer
13. Answer: C. True structures do not typically cross anatomic borders, will usually have well-defined borders and attachments to nearby structures, and can be visualized in multiple views. Artifacts may cross anatomic borders, have indistinct borders and no obvious attachments, and are not seen in multiple views.
14. A mirror-image artifact in two-dimensional echocardiography develops when:
A. A structure is located behind a weak reflector resulting in a mirror-image copy of the structure in a shallower position.
B. A structure is located in front of a highly reflective surface resulting in a mirror-image copy of the structure in a deeper position.
C. A mirror is located in a straight line between the transducer and the structure.
D. A violation in the central beam principle of ultrasound occurs.
View Answer
14. Answer: B. A structure is located in front of a highly reflective surface resulting in a mirror-image copy of the structure in a deeper position. The transducer assumes a single reflection from the strong reflector to the transducer, though on its path back to the transducer, the ultrasound is instead reflected back to the structure and then finally back to the transducer. Given this delay in time to return to the transducer, the image is assumed to be similar but at a greater depth. Therefore, mirror-image artifacts violate the time of flight and straight-line principles of ultrasound. Mirror-image artifacts are duplicates of the original structure that are on the same axis as the transducer beam and the mirror.
15. Which of the following statements is correct regarding ring-down artifact?
A. It is a type of refraction artifact.
B. It is a type of reverberation artifact.
C. It is a type of ultrasound machine artifact caused when the transducer crystal is defective.
D. It is a type of artifact that is not seen in cardiac imaging.
View Answer
15. Answer: B. It is a type of reverberation artifact. Ring-down artifact occurs when the sound beam hits a strong reflector that causes multiple reverberations with distal echogenic lines. Ring down can be caused by gas particles or other strong reflectors. In the gastrointestinal system, when a central fluid collection is trapped by a ring of air bubbles, the pocket of fluid and air may continuously resonate reflecting back ultrasound and creating a bright reflector. Distal to this bright reflector of vibrating fluid and air is a linear beam of ultrasound referred to as a ring-down artifact. In cardiovascular imaging, ring-down artifact is similar to but appears mechanistically different than a comet tail artifact. Strong repetitive reverberations may cause ringing of the transducer crystal and thus the nomenclature of ring-down artifact.
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