Color Doppler twinkling artifact & SPI Ultrasound physics-part 1.

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Back in 1984 I started doing pulse doppler on more than 100 minerals, metals, and other elements after smooth the edge of each item like copper, bones, iron, glass etc. then put the pencil probe with CW doppler perpendicular over it and measures the peak velocity Color and other doppler graphs to find a way to figure out if CW doppler can detect the type of mineral in nature.

I didn't have Color flow like we are having now days, but I found out the early reflections in different shades when I scan bones, stones, and that was my early discovery of the twinkling artifact with non-color doppler. So, I consider myself one of the early sonographers who found out about this phenomenon.

Doppler twinkling artifact is a rapid alternation of colors posterior to a stationary echogenic structure, giving the impact of pseudo dynamicity.

It appears posterior to bright focus instead of grayscale acoustic shadow that’s why it is also called color comet?tail. First time it was introduced and described in 1996 by Rahmouni et al., he described twinkling artifact appeared to be generated by a strongly reflecting medium composed of individual reflectors.

It was concluded that color Doppler signal close to calcifications should be evaluated carefully to eliminate the twinkling artifact. Twinkling artifact is used since long to identify and confirm renal stones, calcification in the liver, thyroid nodules or fibroid, encrusted indwelling urinary stents, bowel gas, metallic foreign bodies and to some extent gallstones, choledocholithiasis, gallbladder adenomyomatosis, hepatic bile duct hamartoma, and chronic pancreatitis.

Nowadays, the twinkling artifact is increasingly used in the identification and differentiation of renal pelvic stones from the adjacent fats in the renal, central echo complex.

Color Doppler twinkling artifact is considered useful on the diagnostic point of view, the clinical significance of this artifact is that; it can differentiate among different echogenic structures.

As for as the mechanism of this artifact is concerned, and hence the exact mechanism is still unknown, but there are two hypotheses regarding twinkling artifacts. First, which was offered by Rahmouni et al.

suggested that when a sound beam is reflected from a rough surface, the acoustic beam split into a complex pattern with phase difference among?

individual wavelets caused by up and down of the surface, resulting in a long spatial pulse length. Doppler ultrasound machine assumes this complex beam pattern as moment of the reflector. it is an intrinsic machine noise probably caused by random time fluctuations in the path lengths of reflected and transmitted sound waves.

It was postulated that slight time fluctuations occur due to sound waves strike against a strong reflector with a rough surface. This slight time variation gives rise to aliased Doppler shifts appear as twinkling artifact

Twinkling artifact is very useful in the detection and confirmation of stones, especially in the urinary tract. It has very high specificity and sensitivity as compared to relaying merely on acoustic shadow in grayscale sonography.

However, the kidney is very richly supplied with blood flow, and the plexus of vessels in the renal hilum and sinus sometimes superimpose on the twinkling artifact, this changing color appearance in a vessel mimic turbulent blood flow.

Intrarenal vascular abnormalities, i.e., arteriovenous fistula and intrarenal artery stenosis cause turbulence and aliasing, but this type of appearance could also be generated by color twinkling artifact caused by a rough surfaced strong reflector such as the kidney stone, foreign?body, or calcification.

Variable color?write priority, gray?scale gain, pulse repetition frequency (PRF), and spectral Doppler gain were varied. They observed that machine settings effect the appearance of the twinkling artifact. It was also evident that rough surface creates more twinkling artifact.?

Ultrasound Artifacts

Ultrasound artifacts represent a false portrayal of image anatomy or image degradations related to false assumptions regarding the propagation and interaction of ultrasound with tissues, as well as malfunctioning or maladjusted equipment.

Understanding how artifacts are generated and how they can be recognized is crucial, which places high demands on the knowledge of the sonographer and the interpreting physician. Most artifacts arise from violations of assumptions for creating the ultrasound image, including but not limited to ultrasound travels at a constant speed in all tissues (1540 m/s);

ultrasound travels in a straight path; reflections occur from the initial ultrasound beam with one interaction at a perpendicular incidence for each boundary; attenuation of ultrasound echoes is uniform;

all of the energy emitted by the ultrasound transducer exists in the main beam; the operator has transmit, receive gain, and other settings properly adjusted; and all of the elements in the transducer array, as well as the remainder of the imaging system, are operating optimally.

Artifacts are caused by a variety of mechanisms that contradict the assumptions listed above. In respective order are responses to these assumptions: Sound travels at different speeds in different media based on compressibility and density characteristics.

The ultrasound system uses the average speed in soft tissue of 1540 m/s to map echo amplitude depths as a function of time in the image matrix. Most notably, for fat with a speed of 1450 m/s (about a 6% difference), echoes along the trajectory, including fat structures, are displaced farther in terms of depth from the actual location.

Even minor differences in ultrasound speed between tissues alter the transmitted beam direction from a straight-line trajectory when the incident ultrasound beam is Non perpendicular to the boundary, causing a change in wavelength (the ultrasound frequency remains constant in stationary tissues).

The transmitted ultrasound beam is redirected at an angle of transmission different from the angle of incidence (known as?refraction), potentially causing mis-mapped anatomic locations.

Multiple reflections of ultrasound occur from all directions within the complex environment of the human body, complicating the mapping of anatomic boundaries in the ultrasound image.

Ultrasound attenuation varies greatly from high to low in typical tissues and structures encountered, with resultant artifactually shadowing or enhancement of tissues at greater depths in the image.

Transducer crystal expansion and contraction in the thickness mode produces the main ultrasound beam, but at the same time radial contraction and expansion also occur. This results in ultrasound energy emitted outside of the main beam producing echoes that can appear as if in the beam and creating false information in the image.

Improper use of user-adjusted overall receive-gain or time gain compensation (TGC) results in images that may not be representative of the acoustic properties at a given depth in the image.

Pulse repetition frequency (PRF) settings must ensure adequate time for listening for echoes before the next pulse. Additionally, proper transducer frequencies must be selected to achieve the desired depth of penetration in the image.

The ultrasound system is dependent on all components of the imaging chain, including the transducer array, gain and filter settings, and image display, to be functioning normally. When there are component failures, the ultrasound images may not be accurately portrayed.

Fortunately, most ultrasound artifacts can be identified by the experienced sonographer because of obvious effects on the image or the transient nature of mis-mapped anatomy that appears and disappears during the scan.

Some artifacts can be used to advantage as diagnostic aids in the characterization of tissue structures and composition. The following descriptions represent some typical artifacts encountered in diagnostic ultrasound.

Refraction

Refraction represents a change in the transmitted ultrasound pulse direction at a boundary with non-perpendicular incidence when the two adjacent tissues support a different speed of sound.

Misplaced anatomy can occur in the image from the beam redirection as the echoes propagate back to the transducer over a similar return path. The sonographer must be aware of objects appearing and disappearing with slight differences in orientation of the transducer array.

At the edges of smooth-rounded organs, refraction of the beam at nonnormal incidence can redirect the beam away from the edge, creating a shadow of reduced intensity beyond the edge and resulting in an edge artifact.

In many situations, the cause of the refraction artifact can be traced back to anatomic structures.

Speed Displacement

The speed displacement artifact results from the substantial variability of sound speed in fat (1450 m/s) relative to soft tissues (1540 m/s)—about a 6% slower propagation speed. Anatomic borders are displaced distally when ultrasound interacts with structures containing fat compared with the nondisplaced borders through the soft tissues.

In the situation of a soft tissue structure surrounded by a fatty liver, the border is proximally displaced behind the soft tissue structure. An image of a liver with a fatty region demonstrates a displacement and disruption of the distal border.

The differences in speed also affect the accuracy of distance measurements along the direction of ultrasound travel when fat is present in the beam.

Shadowing and Enhancement

Acoustic shadowing is the result of several physical mechanisms. Objects with high attenuation, such as kidney stones and gallstones, can assist in diagnosis by producing shadowing or streaks, but they can also be a hindrance if a large attenuator, such as a rib, produces shadows that precludes optimal imaging of distal anatomy.

Shadowing is also the result of reflection and refraction, as shown in the edge shadowing artifact in.

Acoustic enhancement occurs distal to low-attenuation, fluid-filled structures such as cysts and the bladder where increased transmission of sound occurs, resulting in distal hyperintense signals. “Through transmission” is commonly described for this occurrence.

Reverberation, Comet Tail, and Ring-Down

Reverberation artifacts arise from multiple echoes generated between highly reflective and parallel structures that interact at a perpendicular angle to the ultrasound beam.

These artifacts are often caused by reflections between a reflective interface and the transducer or between reflective interfaces, such as metallic objects (e.g., bullet fragments), calcified tissues, or air pocket/partial liquid areas of the anatomy and are typically manifested as multiple equally spaced parallel lines at progressive depth with decreasing amplitude.

Comet tail artifact is a form of reverberation between two closely spaced reflectors and appears as bright lines along the direction of ultrasound propagation. It is manifested as a tapering shape and decreasing width with depth of travel.

Reverberation artifacts are useful in assessing the characteristic structures of tissues but can also hinder visualization of deeper anatomy. Effects of reverberation can be reduced by adjusting the transducer angle of incidence or by decreasing the distance between the reflective structure and the transducer.

Harmonic imaging reduces these artifacts by receiving the first harmonic frequency and filtering out the fundamental frequency.

Ring-down artifacts arise from resonant vibrations within fluid trapped between a tetrahedron of air bubbles, which creates a continuous sound wave that is transmitted back to the transducer and displayed as a series of parallel bands extending posterior to a collection of gas.

Mirror Image and Multipath Reflection

Mirror image artifacts occur when the ultrasound beam encounters a highly reflective non-perpendicular or curved boundary such as the diaphragm.

The redirected beam encounters a specular reflector, producing a series of echoes that are reflected along the same path back to the transducer. As the field of view is scanned,

the beam interacts with the same specular reflector to record its true position. Later echoes of the specular reflector from the redirected beam arrive and are mapped as distal objects on the opposite side of the strong reflector, appearing as a mirror image because of the double reflection.

A common mirror image artifact occurs at the interface of the liver and the diaphragm in abdominal imaging. In one direction, the ultrasound beam correctly positions the echoes emanating from a lesion in the liver.

As the ultrasound beam moves through the liver, echoes are strongly reflected from the curved diaphragm away from the main beam to interact with the lesion, generating echoes that travel back to the diaphragm and ultimately back to the transducer.

The back-and-forth travel distance of these echoes creates artifactually anatomy that resembles a mirror image of the mass, placed beyond the diaphragm that would otherwise not have anatomy present in the image

Other strong reflectors that generate mirror image artifacts include the pericardium and bowel, which might be more difficult to detect due to the presence of other anatomic structures in the same area.

As a Point of Care Ultrasound (POCUS) enthusiast, you may dread the term “Ultrasound Physics” and wished there was a simple way on how to learn and understand the principles of ultrasound physics that are?actually relevant?to your clinical practice.

But many of the resources on ultrasound physics that you encounter may seem too technical or don’t actually relate to the clinical use of Point of Care Ultrasound (POCUS).

What is the Definition of Ultrasound?

The definition of “ultrasound” is simply the vibration of sound with a frequency that is above the threshold of what humans can hear. The frequency of ultrasound is by definition, any frequency greater than 20,000 Hz. However, ultrasound used in medical practice is typically 1,000,000 Hz (1 Megahertz) or greater.

So the next time you pick up an ultrasound probe or transducer just notice what “Frequency” the probe is. It will usually range (termed?bandwidth) between 2 Megahertz to 10 Megahertz. For example, 2.5-3.5 MHz for general abdominal imaging and 5.0-10 MHz for superficial imaging.

How Ultrasound Creates a Picture – The Piezoelectric Effect

Next let’s go over how an ultrasound device uses ultrasonic waves to create pictures on the screen for you.

It traditionally does this by using an effect called the?“Piezoelectric Effect.” This is simply the vibration of a piezoelectric crystal at the tip of the transducer that generates a specific ultrasonic frequency to create ultrasound waves. (FYI These crystals are easily broken and cost thousands of dollars to replace. Think about that each time you drop a probe. Yikes!)

These ultrasonic waves can then penetrate through the body’s soft tissue and return to the transducer as reflected ultrasound waves. These returning waves are then converted into an ultrasound image on the screen for you to view.

Therefore, all ultrasound principles are based on the physics of “waves” and if you can understand some basic physics principles that pertain to waves, you can derive exactly how ultrasound images are formed, ultrasound artifacts are created, and even how to use more advanced ultrasound applications such as Doppler.

Just think of Ultrasound in terms of “Waves”

An ultrasound device creates images, simply by sending short bursts of “waves” into the body. Understanding how these waves behave will be helpful in understanding how to optimize your ultrasound settings and images. I’ll make it as simple as possible for you and just go over the things I have found to be most relevant to be able to use the ultrasound machine.

Frequency and Wavelengths

Now I’m sure you’ve heard the word “Frequency” a lot when it comes to ultrasound transducers. Such as high versus low frequency ultrasound probes. But what exactly does that mean? Okay let’s get some definitions out of the way:

Wavelength?= length or distance of a single cycle of a wave.

Frequency?= the number of sound wave cycles per second.

The equation for?Frequency = Speed of sound wave/Wavelength

So you can see from the equation, as wavelength increases, frequency decreases (and vice versa). This is because Frequency is inversely related to wavelength. The SHORTER the wavelength the HIGHER the frequency and the LONGER the wavelength the LOWER the frequency.

This is why higher frequency ultrasound probes will give you better resolution compared to a lower frequency probe. A high-frequency ultrasound probe will emit shorter wavelengths, so tissues will receive more ultrasound “waves” per unit of time with a high-frequency probe.

However, the trade-off with high-frequency probes is decreased penetration because the piezoelectric crystal can only send so many ultrasound waves out before the waves dissipate.

Speed of Sound in Different Mediums, and that was my first research I worked on for more than 100 different materials back in 1984.

Now the “speed of sound” is also often referred to with ultrasound. So why is the speed or velocity of sound so important?

Well, the exact speed of sound in specific tissue does not actually mean much to you clinically. However, the?change in speed?between two different mediums is extremely important. This is the essence of how ultrasound waves reflect and refract to create important ultrasound artifacts.

So while you don’t need to know the exact speed of sound in certain tissue you do need to understand how the speed of sound changes between different mediums such as soft tissue, fluid, air, and bone.

The average speed/velocity of sound in all mediums is 1540 cm/s. However, depending on what medium the sound waves travel through, it can drastically change the propagation speed of sound as it passes through.

Two of the factors that affect the speed of sound are the?stiffness and density?of the material it is traveling through. The stiffer the medium, the faster the sound waves will travel and that is why sound waves travel faster in solids than in liquids or gases. So the ultrasound propagation speed from slowest to fastest is: Lung (air) << Fat < Soft tissue << Bone. This happens because stiffer mediums have tighter particles to propagate the ultrasound wave and therefore the velocity is greater.

Acoustic Impedance – Reflection and Refraction

Acoustic Impedance?is the Resistance to Ultrasound Propagation as it Passes Through a Tissue

Acoustic Impedance is probably one of the most confusing terms when trying to learn ultrasound physics.

Acoustic Impedance (Z) is actually a physical property of a medium or tissue. It is dependent on the tissue density and the speed of sound through that tissue.

Impedance?= Density x Propagation Speed of Sound Wave

So if the density of a tissue increases, the impedance (resistance) will increase as well. Refer to the ultrasound physics table again:

Reflection of Ultrasound Waves

The importance of Impedance in ultrasound becomes apparent at the interface of two tissue types with significantly different impedance values. Ultrasound waves will reflect when this situation occurs. The proportion of ultrasound waves reflected back is proportional to the difference in impedance (or density) of two tissue types.

REFLECTION?occurs with ultrasound waves when two adjacent tissues have?Significantly Different Impedance Values.

This is why bone and air appear as bright lines on ultrasound and also why you get the reflected “A-Lines” with pulmonary ultrasound. There is such a large difference between impedance of tissue and bone/air that they will cause almost all of the ultrasound waves to reflect back instead of penetrating through. What is interesting is that the impedance values of Air (extremely low at 0.0004) and bone (very high at 12), both cause reflection because of its drastic difference from the impedance of soft tissue (approximately 1.6).

Refraction of Ultrasound Waves

REFRACTION?occurs with ultrasound waves when two adjacent tissues have?Slightly Different Impedance Values.

So when ultrasound waves travel through tissue and meet another tissue with slightly different impedance values, the speed changes somewhat and cause the ultrasound waves to change in direction. This change in direction is called Refraction!

The degree of how much refraction occurs is dependent on what angle the ultrasound wave encounters the second medium and how much of a change in speed there is in the second medium.

This is seen mostly in situations at the rounded interfaces between a fluid-filled circular structure and the adjacent soft tissue. This is what gives rise to the edge artifact seen in ultrasound with black lines arising from the edge of fluid-filled structures such as the gallbladder, cyst, vessels, and bladder.

Attenuation – Absorption

ATTENUATION?is the Loss and Absorption of Ultrasound Energy Through a Medium

Attenuation is a fairly easy concept to understand compared to impedance. It just describes how rapidly does a medium reduce the intensity of an ultrasound wave as it passes through it. The two mediums with the highest amounts of attenuation are actually AIR and BONE!

As you can see attenuation is not simply dependent on the density of the material like impedance is. Look at ultrasound physics table below to see the relationship between tissue density, impedance, and attenuation:

This is the reason that ultrasound waves can’t pass through air or bone. The ultrasound waves either get reflected back (impedance mismatch) or gets absorbed (high attenuation).

Attenuation will account for the “Shadowing” artifact seen in bone or gall stones.

“Echogenicity” refers to how bright (echogenic) a tissue appears on ultrasound relative to another tissue.

Anechoic?(Black)

The term?“Anechoic”?on ultrasound means no internal echoes are emitted and there is a completely black appearance. This is most commonly seen with fluid-filled structures since ultrasound waves pass through fluid without reflecting any echoes back to the ultrasound machine.

Here is a list of structures that appear “Anechoic” or black on ultrasound: blood (unclotted), bladder, transudative pleural effusions, ascites, simple cysts, gallbladder.

Hyperechoic?(Bright/White)

The term “Hyperechoic” on ultrasound means that a specific structure gives off MORE echoes relative to its surrounding structures resulting in a brighter/whiter appearance. Below is an example of the pleural line which is “Hyperechoic” (bright/white) compared to the surrounding soft tissue.

Hypoechoic?(Darker/Grey)

The term?“Hypoechoic” on ultrasound means that a specific structure gives off fewer echoes relative to its surrounding structures resulting in a darker or more grey appearance.

In the image below this patient has hepatitis with a Hypoechoic (darker) appearing liver compared to the right kidney:

Isoechoic (Similar)

The term?“Isoechoic”?on ultrasound means that a specific structure gives off similar echoes relative to another structure on the ultrasound screen. For example, you may say the Renal Cortex is isoechoic to the Spleen Parenchyma like the image below:

Ultrasound Doppler?

One of the most used modes with ultrasound is Doppler. Initially, Doppler may seem confusing with all of the different Doppler modes available to you (color Doppler, power Doppler, pulse wave Doppler, continuous wave Doppler, and tissue Doppler).

But if you just think of Doppler signals as detecting the speed of movement either Towards or Away from your probe you can derive all of the different Doppler ultrasound modes.

The Doppler Effect (or Doppler Shift) is used to evaluate movement either towards or away from the ultrasound probe/transducer. The most common Doppler ultrasound application we think of is detecting movement of blood, but we can also use Doppler on ultrasound to evaluate tissue and muscle movement.

Doppler Shift Equation:

Doppler Shift?= (2 x?Velocity of blood?x transducer frequency x?cos?θ)/ Propagation speed

*θ?=?Angle of Insonation?(angle of incidence between the ultrasound beam and the direction of flow)

So, the Doppler shift is mainly related to TWO things:

1. The Velocity of the blood cells
2. The Angle of Insonation

So the most important thing you can do to improve your Doppler technique for any mode is to make sure that the movement of whatever you are measuring is parallel to your ultrasound probe as much as possible (zero degrees). Anything above 25-30 degrees will significantly underestimate your measurements. And if you are perpendicular, the cosine of 90 degrees = 0 and the ultrasound Doppler will read no flow or movement.

Color Doppler

The most common Doppler mode you will use is color Doppler. This mode allows you to see the movement of blood movement in arteries and veins with blue and red patterns on the ultrasound screen.

A common question that comes up with color Doppler is:?What do the colors on ultrasound mean??The answer is: RED means there is flow TOWARDS the ultrasound probe and BLUE means that there is flow AWAY from the ultrasound probe. It is a misconception that red is arterial and blue is venous. It actually just depends on the direction blood is flowing relative to the angle of your ultrasound beam.

An easy way to remember this is to use the?BART mnemonic:?Blue AWAY,?Red TOWARDS.

There is a mode similar to color Doppler that you may encounter called Power Doppler. This mode does not show up as red or blue on the screen but only uses a single yellow color signifying the amplitude of flow. It is more sensitive than color Doppler and is used to detect low flow states such as venous flow in the thyroid or testicles.

The “Other Doppler Modes”

Now some learners may feel like the “other doppler modes” such as?Pulse wave, Continuous wave, and Tissue Doppler?are very advanced settings. However, the same principles of color Doppler apply to these other Doppler modes as well. The ultrasound probe is just detecting flow or motion either TOWARDS or AWAY from it. If it is towards the probe there will be a positive deflection and if it is away from the probe there will be a negative deflection.

Essential Ultrasound Artifacts

Ultrasound artifacts are frequently encountered and can be a source of confusion for interpreting providers. Ultrasound artifacts can be understood with a basic understanding of the ultrasound physics we just discussed pertaining to reflection, refraction, and attenuation.

The ability to recognize and fix correctable ultrasound artifacts is important for getting quality ultrasound images and optimizing the care of your patients.

My sets of questions and answers will also cover all the the ultrasound artifacts such as:

• Mirror Image Artifact
• Acoustic Shadowing Artifact
• Posterior Acoustic Enhancement
• Edge Shadowing Artifact
• Reverberation Artifact
• Comet Tail Artifact
• Ring Down Artifact
• Side Lobe Artifact

Mirror Image Artifact

The mirror image artifact on ultrasound occurs when ultrasound waves encounter a highly reflective surface that is adjacent to air.

The most common instance of this is the pleural-diaphragm interface causing the appearance of “liver” or “spleen” inside the lung. You can also see mirror image artifact when you are performing cardiac ultrasound as the ultrasound waves, approach the pleural-pericardium interface. These are normal findings.

Acoustic Shadowing Artifact

Acoustic shadowing occurs when ultrasound waves encounter a structure that has a high attenuation coefficient.

You will most commonly encounter the acoustic shadowing artifacts in the following structures: bones, ribs, and gallstones.

Posterior Acoustic Enhancement

This is the opposite of the acoustic shadowing artifact and occurs when ultrasound waves pass through a structure with significantly low attenuation such as blood or fluid-filled structures.

The most common situation you will see posterior acoustic enhancement: bladder, gallbladder, cysts, vessels, ocular ultrasound.

Edge Shadowing Artifact

Edge artifact on ultrasound occurs because of refraction. Ultrasound waves are deflected from their original path when they encounter curved and smooth-walled structures. This will result in a shadow-like line that comes off of the edge of these structures. The most common times you will see this are: vessel walls, gallbladder, cystic structures, testicle, aorta.

Reverberation Artifact

In the presence of highly reflective surfaces, echoes may reflect back and forth between the reflective surface and the ultrasound probe. This can cause the ultrasound screen to record and display multiple echoes on the screen. This ultrasound artifact is known as Reverberation Artifact.

Let’s use the highly reflective pleural line as an example below. The ultrasound waves that return after a single reflection represents the actual pleural line (white arrows/line in the figure below).

All of the subsequent echoes (blue, green, and red arrows/lines) will take longer to return the probe and the ultrasound will interpret those as increased equidistantly spaced linear reflections. These other lines are also known as “A-lines” and are a form of reverberation artifact in normal lung.

Comet Tail Artifact

Comet tail artifact is a form of reverberation artifact. In comet tail artifact the two reflective surfaces are closely spaced together (such as the bevel of a metallic needle). The reflective surfaces are so close that it is difficult to distinguish between each reflected echo.

Comet tail artifact is different from ring down artifact (described next) because the comet tail artifact dissipates with depth and has a triangular and tapered shape. See the image below of a comet tail artifact arising from a needle tip.

Ring Down Artifact

Previously, the ring down artifact was thought to be a type of comet tail artifact, since both have bright “echogenic” lines arising from a specific location. However, the ring down artifact has a distinct feature compared to the comet tail artifact in that the echo's do NOT dissipate as the depth of the image is increased.

These echogenic vertical lines will go all the way to the bottom of the screen, regardless of depth. This has become known as the “ring down artifact” and is most commonly seen as “B-lines” in lung ultrasound, signifying interstitial edema.

The theory for the ring down artifact is that when fluid is trapped in a tetrahedron of air bubbles, the ultrasound waves reflect infinitely and result in an infinitely long vertical echogenic line.

Side lobe Artifact

Side lobe artifact occurs when the beam of an off-axis side lobe encounters a structure and returns this off-axis object as coming from the main beam. This creates a duplicate structure on the screen but in a different area.

In the example below, it seems like there is a moving structure in the left atrium, but it is actually a side lobe artifact resulting from the mitral valve leaflet. This is important because oftentimes these side lobe artifacts may be mistaken for clots or foreign bodies. It is always a good habit to get multiple views to confirm that what you are seeing is artifact versus pathology.

Best Ultrasound Physics Book Reference – Sidney K. Edelman PhD

I hope you found this ultrasound physics post helpful and clinically relevant. Of course, I could not cover every detail of ultrasound physics in one post, but if you went through this post, you would have all the ultrasound physics basics to help your scanning.

However, if you want to learn more about ultrasound physics, I recommend checking out this book by Sidney K. Edelman PhD. It will go over all of the ultrasound physics you could ever want but in a very reader-friendly way. It’s definitely a staple on my ultrasound bookshelf!

Some of the questions and answers in my (3000) sale set example ;

Name and describe the two useful imaging artifacts?

The two attenuation artifacts are shadowing and enhancement.

1-Shadowing: the weakening of echoes distal to a strongly attenuating or reflecting structure or from the edges of a refracting structure.

2-Enhancement: the strengthening of echoes distal to a weakly attenuating structure.

Which artifacts are reduced with spatial compounding?

Spatial compound is the averaging of frames that view anatomy from different angles. Several approaches to each anatomical site are used allowing the beam to "get under" the attenuating or enhancing structure. This is useful with shadowing because it can uncover structures located in the shadow. It can also reduce the effects of enhancement.

How are side lobes and grating lobes similar?

Similar: Side lobe and grating lobes are additional weak sound beams that travel in different directions than the primary beam. They normally do not produce echoes that are displayed on the image.

The mirror image artifact is a form of ________.

Reverberation

If the pulse repetition frequency (PRF) is 10 kHz, what Doppler shift would produce aliasing?

Doppler shifts greater than 5 kHz would produce aliasing.

Refraction displaces structures ____________ from their correct location.

Laterally

Define aliasing.

Aliasing indicates improper representation of information that has been insufficiently sampled. It is the appearance of Doppler information on the wrong side of the baseline. It occurs when the Nyquist limit has been exceeded. The Nyquist limit is equal to one half of the PRF.

What is range ambiguity?

Range ambiguity occurs when all echoes are not received before the next pulse is emitted. . The range ambiguity artifact places structures much closer to the surface than the correct location.

How can range ambiguity be eliminated in pulse Doppler?

Decreasing the pulse repetition frequency will eliminate range ambiguity.

What would occur if the propagation speed of soft tissue was greater than 1.54 mm/μs?

If the propagation speed exceeds 1.54 mm/us, the calculated distance to the reflector is too small, and the display will place the reflector too close to the transducer (too shallow). This occurs because the increased speed causes the echoes to arrive sooner than anticipated by the ultrasound system.

00:0201:30

Give an example of an optical form of temporal aliasing.

An example of optical temporal aliasing can be demonstrated in motion pictures when wagon or car wheels appear to rotate at various speeds and reverse direction.

What is the importance of the Nyquist limit?

The Nyquist limit is the upper limit of Doppler shift that can be detected properly by pulsed instruments. It is equal to one half of the pulse repetition frequency.

Name an advantage of continuous-wave Doppler ultrasound.

Advantage: Continuous-wave Doppler does not experience aliasing.

List the sonographic artifacts included in the propagation group.

Comet tail, grating lobe, mirror image, range ambiguity, refraction, reverberation, ring down, slice (section) thickness, speckle, and speed error.

List the sonographic artifacts included in the attenuation group.

Enhancement, focal banding (enhancement), edge shadow (refraction), and shadowing

Describe slice thickness artifact.

Echoes from the third dimension perpendicular to scan plane of the sound beam are included in the two-dimensional image.

What is a comet-tail artifact?

Comet-tail artifact is a form of reverberation, when two closely spaced surfaces generate a series of closely spaced discrete echoes.

What is clutter?

Clutter is as also called the flash artifact, resulting from tissue, heart wall or valve, or vessel wall motion. Such clutter is eliminated by wall filters.

List ways to eliminate aliasing

Ways to eliminate aliasing include shifting the baseline, increasing the PRF, decreasing the Doppler angle, decreasing the distance to the sample volume (which increases the PRF), and using CW Doppler.

How are side lobes and grating lobes different?

Different: Side lobes are beams propagated from a single element while grating lobes are additional beams emitted from an array transducer.

What can cause range ambiguity

High PRF can cause range ambiguity in spectral and color Doppler.

How to avoid range ambiguity

To avoid range ambiguity, PRF automatically reduces in deeper imaging, and multiple sample volumes may appear

How to get rid of slice thickness artifact

It may be possible to resolve this artifact using harmonic imaging, because the sound beam in this mode is narrower than in the conventional gray-scale mode.

References

1. Ultrasound physics book by Sidney Eidelman, PhD.
2. Dr kremkua physics book .
3. Feldman, M., Katyal, S., Blackwood, M.?(2009).?US artifacts.?Radiographics: a review publication of the Radiological Society of North America, Inc 29(4), 1179 – 1189.

You can also read many articles in my blog, www.moleopedia.com under the ultrasound section, and ultrasound cases section.

For those who wants to pass the SPI- ARDMS national exam ,you can email me to buy my designed 3000 questions and answers to cover everything in the national exam.it is only 100 usa dollars , 99% passing rate.

Steve Ramsey, PhD.