Master the ultrasound artifacts most likely to appear in SPI-style questions, including reverberation, comet tail, ring-down, mirror image, shadowing, enhancement, refraction, side lobes, beam-width artifact, speed error, range ambiguity, and Doppler artifacts.
Quick Answer
For the SPI exam, knowing an artifact’s name is not enough.
You should be able to answer three questions:
- What does the artifact look like?
- What physical assumption or interaction caused it?
- What scanning adjustment can reduce or confirm it?
The current ARDMS SPI content outline explicitly expects candidates to recognize and modify scanning technique in response to gray-scale artifacts, while image optimization and Doppler together make up a large portion of the exam.
The most important artifacts to know are:
- Reverberation
- Comet-tail
- Ring-down
- Posterior acoustic shadowing
- Posterior acoustic enhancement
- Mirror image
- Refraction
- Edge shadowing
- Side-lobe artifact
- Grating-lobe artifact
- Beam-width artifact
- Speed-displacement error
- Range ambiguity
- Slice-thickness artifact
- Speckle
- Aliasing
- Spectral mirror artifact
A good SPI rule is:
Appearance → Cause → Correction
If you understand that chain, artifact questions become much easier.
Why Ultrasound Artifacts Are High-Yield for SPI
Ultrasound systems make assumptions.
For example, the machine generally assumes that:
- Sound travels in a straight line.
- Sound travels at approximately 1,540 m/s through soft tissue.
- Echoes return directly from the structure that created them.
- The strongest echo came from the main beam.
- Each transmitted pulse returns before the next pulse is sent.
- The displayed depth is proportional to travel time.
When one of these assumptions is violated, the system can place echoes:
- Too deep
- Too shallow
- In the wrong location
- Multiple times
- Inside a structure that should be anechoic
- On the wrong side of a spectral baseline
That is how many artifacts are created.
A recent SPI-focused artifact guide published in September 2026 also reflects how active this keyword cluster currently is in search, with particular attention to reverberation, comet tail, ring-down, shadowing, enhancement, mirror image, and refraction.
Start With the Most Important Distinction
An artifact is not always “bad.”
Some artifacts:
- Reduce image quality.
- Create false anatomy.
- Hide pathology.
Others can actually help identify tissue characteristics.
For example:
Posterior acoustic shadowing
May support the presence of a highly attenuating structure such as a calcification or stone.
Posterior acoustic enhancement
May help confirm that a structure contains fluid.
So on the SPI exam, do not assume:
“Artifact = always remove it.”
Sometimes the artifact itself provides useful diagnostic information.
Reverberation Artifact
Reverberation occurs when sound repeatedly reflects between two strong interfaces.
Instead of returning to the transducer once, the sound bounces back and forth before finally returning.
The machine assumes each delayed echo traveled directly from a deeper structure.
So it places each additional echo progressively deeper.
What Reverberation Looks Like
Typical appearance:
- Multiple bright parallel echoes
- Approximately equally spaced
- Repeated deeper than the actual reflector
- Echoes may become weaker with depth
A common setup involves:
- Strong reflectors
- Interfaces near the transducer
- Metallic or highly reflective structures
Why the Echoes Are Equally Spaced
Suppose sound bounces between:
- Transducer
- Strong reflector
Each additional round trip takes approximately the same extra amount of time.
The scanner converts that additional travel time into additional depth.
That creates repeated echoes at regular intervals.
Reverberation SPI Shortcut
Multiple equally spaced lines = reverberation
How Can You Reduce Reverberation?
Possible adjustments include:
- Changing the transducer angle
- Changing the acoustic window
- Using tissue harmonic imaging
- Reducing unnecessary gain where appropriate
Changing the scanning angle can break the repeated reflection pathway.
Comet-Tail Artifact
Comet tail is generally considered a short-path reverberation-type artifact.
It appears when sound repeatedly reflects between closely spaced strong reflectors.
What Comet Tail Looks Like
Usually:
- Bright
- Short
- Tapering
- Immediately behind a strong reflector
It may appear as a dense trail of echoes rather than clearly separated horizontal lines.
Reverberation vs. Comet Tail
Reverberation
Usually:
- Multiple
- Distinct
- Equally spaced echoes
Comet Tail
Usually:
- Shorter
- Tapered
- Dense bright trail
Do not automatically label every bright tail as ring-down.
Ring-Down Artifact
Ring-down is associated with resonance involving gas bubbles.
It may appear as:
- Continuous bright band
- Echogenic streak extending deeper from gas
Current SPI artifact resources distinguish ring-down from the discrete repeated lines of standard reverberation.
Comet Tail vs. Ring-Down
This is a favorite conceptual distinction.
Comet Tail
Generally associated with repeated reflections between closely spaced strong reflectors.
Ring-Down
Associated with continuous resonance involving gas bubbles.
Visually, both can appear as bright trails.
The mechanism is what separates them.
Posterior Acoustic Shadowing
Shadowing occurs when a structure strongly:
- Attenuates
- Absorbs
- Reflects
the ultrasound beam.
Very little sound continues beyond the structure.
The area behind it receives fewer returning echoes.
What Shadowing Looks Like
A dark region:
posterior to a highly attenuating structure
Common examples may occur behind:
- Stones
- Calcifications
- Bone
- Gas
Why Shadowing Happens
Think:
“Not enough sound gets through.”
Less transmitted energy reaches deeper tissues.
Therefore:
Fewer echoes return from behind the structure.
Shadowing SPI Shortcut
Bright structure + dark region behind it = posterior acoustic shadowing
Clean vs. Dirty Shadowing
Students may encounter these terms in clinical sonography.
Clean shadowing
More sharply defined dark shadow, often associated with highly attenuating solid reflectors.
Dirty shadowing
More irregular shadowing often associated with gas and reverberation.
For SPI, focus first on the physics:
strong attenuation or reflection reduces energy distal to the structure.
Edge Shadowing
Edge shadowing appears along the edge of a curved structure.
It is often related to refraction.
As the beam encounters a curved interface at an oblique angle, the beam bends away.
Less sound reaches the region immediately behind the edge.
This creates a narrow shadow.
Posterior Acoustic Enhancement
Enhancement is essentially the opposite of shadowing.
It occurs when sound travels through a structure that attenuates the beam less than surrounding tissues.
More sound reaches the deeper tissues.
Therefore the region behind the structure appears brighter.
What Enhancement Looks Like
- Increased echogenicity
- Distal to a low-attenuation structure
- Often seen behind fluid
Why Fluid Produces Enhancement
Fluid generally attenuates sound less than many surrounding soft tissues.
So more ultrasound energy remains after traveling through it.
The tissues behind the fluid receive more sound and return stronger echoes.
Enhancement SPI Shortcut
Anechoic/fluid structure + increased brightness behind it = enhancement
Shadowing vs. Enhancement
| Artifact | What Happens to Sound? | Appearance Behind Structure |
|---|---|---|
| Shadowing | Strong attenuation | Darker |
| Enhancement | Low attenuation | Brighter |
This contrast is worth memorizing.
Mirror Image Artifact
Mirror image creates a duplicated structure on the opposite side of a strong reflector.
A common reflector capable of producing this artifact is a strong curved interface.
How Mirror Image Happens
Sound reaches a strong reflector and takes an indirect path.
The system assumes:
- Sound traveled straight.
- The returning echo came directly from the displayed location.
Because the indirect path took longer, the machine places the duplicated structure:
- Deeper
- On the opposite side of the reflector
What Mirror Image Looks Like
You may see:
- Real anatomy
- Strong reflector
- Duplicate copy of anatomy beyond the reflector
The duplicate may appear:
- Similar shape
- Similar distance relative to the reflector
Mirror Image SPI Shortcut
Duplicate anatomy across strong reflector = mirror image
How to Reduce or Confirm Mirror Artifact
Possible approach:
- Change transducer position
- Change insonation angle
- Use another acoustic window
A true anatomical structure should remain anatomically consistent.
An artifact may change or disappear when the beam path changes.
Refraction Artifact
Refraction means the ultrasound beam changes direction when crossing an interface at an oblique angle where propagation speeds differ.
The machine still assumes:
The beam traveled in a straight line.
That can cause anatomy to appear displaced.
Refraction Can Cause Duplication
One important consequence is lateral duplication.
A single structure may appear as two structures.
Refraction SPI Shortcut
Think:
Bent beam → wrong lateral position
Snell’s Law Concept
You generally do not need to turn every SPI question into advanced trigonometry.
The important idea is:
Refraction requires:
- Oblique incidence
- Different propagation speeds across the interface
At perpendicular incidence, refraction does not occur in the same way.
Speed-Displacement Error
The ultrasound system assumes sound travels through soft tissue at:
1,540 m/s
But actual propagation speed varies by material.
If sound travels through tissue faster or slower than the assumed speed, the scanner may place the reflector at the wrong depth.
If Sound Travels Slower Than 1,540 m/s
The echo takes longer to return.
The system assumes the structure must be deeper.
Therefore the reflector is displayed:
Too deep
If Sound Travels Faster Than 1,540 m/s
The echo returns sooner.
The system assumes the reflector is closer.
Therefore it is displayed:
Too shallow
Speed Error Memory Trick
Slower sound
Longer return time → displayed deeper
Faster sound
Shorter return time → displayed shallower
Side-Lobe Artifact
Side lobes are weak beams of sound that travel outside the main ultrasound beam.
If a side lobe encounters a strong reflector:
- An echo returns.
- The system assumes it came from the main beam.
The echo is therefore placed incorrectly.
What Side-Lobe Artifact May Look Like
False echoes may appear:
- Inside a cyst
- Inside a fluid-filled structure
- In an area that should be anechoic
Side-Lobe SPI Shortcut
Off-axis sound → echo displayed as if it came from main beam
Grating-Lobe Artifact
Grating lobes are similar in concept to side lobes but are associated particularly with array transducers.
They can produce off-axis energy that creates misplaced echoes.
Again, the core principle is:
The scanner assumes the echo originated from the main beam.
Beam-Width Artifact
The ultrasound beam has physical width.
If part of the beam encounters a strong reflector while another part passes through fluid, the returning echo may be assigned to the fluid-filled region.
This can create false internal echoes.
Beam-Width Artifact Example
A cyst should appear anechoic.
However, the beam is wider than the cyst.
Part of the beam strikes adjacent tissue.
The system places some of those echoes inside the cyst.
The cyst appears to contain debris even when it does not.
Beam-Width vs. Side-Lobe Artifact
Both can create false echoes inside fluid structures.
Side lobe
Energy exists outside the main beam.
Beam width
The actual main beam itself is wider than the structure.
Know the mechanism.
Slice-Thickness Artifact
Slice thickness is essentially the elevational dimension of the beam.
If the slice includes both:
- Fluid
- Adjacent tissue
echoes from outside the intended imaging plane may appear inside the fluid structure.
This is often considered the three-dimensional equivalent of beam-width artifact.
How to Reduce Slice-Thickness Artifact
Possible strategies include:
- Reposition the transducer
- Change imaging plane
- Use better elevational focusing
- Use a different transducer where appropriate
Range Ambiguity
Range ambiguity occurs when an echo from one pulse returns after the next pulse has already been transmitted.
The machine may assign the late echo to the wrong pulse.
As a result, the reflector is displayed at an incorrect depth.
When Is Range Ambiguity More Likely?
When PRF is very high.
Why?
The system sends pulses so rapidly that late echoes from deeper structures may arrive after the next pulse has already begun.
Range Ambiguity Memory Trick
PRF too high → system confuses which pulse produced the echo
Speckle
Speckle is the granular texture commonly seen in ultrasound images.
It results from interference between echoes returning from many small scatterers.
Speckle can:
- Reduce contrast resolution
- Make tissue appear grainy
Modern processing methods may attempt to reduce speckle while preserving anatomical information.
Spatial Compounding and Artifacts
Spatial compounding combines images acquired from different insonation angles.
It may help reduce some angle-dependent artifacts such as:
- Speckle
- Edge shadowing
- Certain reverberation patterns
But it may also reduce artifacts that are diagnostically useful.
Again:
Not every artifact should automatically be eliminated.
Harmonic Imaging and Artifacts
Tissue harmonic imaging uses harmonic frequencies generated as sound propagates through tissue.
Harmonic imaging may improve image quality by reducing certain:
- Reverberation artifacts
- Side-lobe artifacts
- Near-field clutter
It can also improve contrast resolution in some imaging situations.
Aliasing
Aliasing is a Doppler artifact.
It occurs when:
Doppler shift > Nyquist limit
and:
Nyquist Limit = PRF / 2
You already have a dedicated Medical Hero article on aliasing, so internally link to it rather than repeating the entire topic.
What Aliasing Looks Like
Spectral Doppler
Waveform wraps around the display.
Color Doppler
Color abruptly wraps to the opposite end of the color map.
The flow may appear to reverse even though true direction has not changed.
Spectral Mirror Artifact
Spectral mirror artifact creates a duplicate Doppler waveform on the opposite side of the baseline.
This may occur with:
- Excessive Doppler gain
- Strong signals
- Small Doppler angles
Aliasing vs. Spectral Mirror
Aliasing
Waveform wraps because Nyquist limit is exceeded.
Spectral Mirror
A duplicated waveform appears across the baseline.
They may both place information on the opposite side of the baseline, but the mechanisms are different.
Flash Artifact
Color flash artifact occurs when tissue or transducer motion creates low-frequency Doppler shifts that appear as sudden bursts of color.
Possible causes include:
- Patient motion
- Transducer movement
- Vessel-wall motion
How to Reduce Flash Artifact
Possible adjustments:
- Reduce transducer motion
- Increase wall filter when appropriate
- Adjust color gain
- Stabilize the scanning technique
Be careful:
A high wall filter can also eliminate real slow flow.
Blooming / Color Bleeding
Excessive color gain can cause color to extend beyond the actual vessel walls.
This may make the vessel appear larger or suggest flow where none exists.
Correction:
Reduce color gain.
Artifact Questions Often Test Machine Controls
A strong SPI question may ask:
A cyst contains false internal echoes. What should the sonographer do?
Possible approaches may include:
- Change transducer angle
- Reposition the patient
- Use harmonics
- Adjust focus
- Rescan in another plane
The best answer depends on the suspected artifact.
Artifact Scenario 1: Repeated Parallel Lines
An image shows several equally spaced echoes deep to a strong reflector.
Most likely artifact:
Reverberation
Reason:
Repeated back-and-forth reflections.
Artifact Scenario 2: Bright Region Behind a Cyst
A simple cyst is anechoic and the tissue behind it appears brighter.
Artifact:
Posterior acoustic enhancement
Cause:
Low attenuation through fluid.
Artifact Scenario 3: Dark Region Behind a Stone
A highly echogenic structure creates a dark region posteriorly.
Artifact:
Posterior acoustic shadowing
Cause:
Strong attenuation or reflection.
Artifact Scenario 4: Duplicate Anatomy Across the Diaphragm
A structure appears duplicated on the opposite side of a strong reflector.
Artifact:
Mirror image
Artifact Scenario 5: False Echoes Inside a Cyst
The cyst should be anechoic, but low-level internal echoes appear.
Possible causes include:
- Side lobes
- Beam-width artifact
- Slice-thickness artifact
The question stem should provide clues about the mechanism.
Artifact Scenario 6: Structure Appears Too Deep
Sound travels through a medium with propagation speed slower than assumed.
The system measures a longer return time.
Result:
Structure displayed too deep
Artifact Scenario 7: High PRF and Misplaced Deep Echo
A delayed echo from a previous pulse is assigned to the next pulse.
Artifact:
Range ambiguity
The Fastest SPI Artifact Method
When you see an artifact question, ask:
1. Is the problem axial, lateral, or Doppler?
Where is the error displayed?
2. Is the image repeated, missing, displaced, or falsely filled?
That narrows the mechanism.
3. Which ultrasound assumption failed?
Examples:
- Straight-line propagation
- 1,540 m/s speed
- Direct return path
- Main-beam origin
- Correct pulse assignment
4. What scanner adjustment affects that mechanism?
Do not randomly change gain.
High-Yield Artifact Table
| Artifact | Appearance | Main Cause |
|---|---|---|
| Reverberation | Repeated parallel echoes | Multiple reflections |
| Comet tail | Short bright tapering trail | Closely spaced reverberations |
| Ring-down | Continuous bright trail | Gas resonance |
| Shadowing | Dark distal region | Strong attenuation |
| Enhancement | Bright distal region | Low attenuation |
| Mirror image | Duplicate anatomy | Indirect reflection path |
| Refraction | Displaced/duplicated anatomy | Beam bending |
| Side lobe | False echoes | Off-axis energy |
| Beam width | False echoes in fluid | Beam wider than structure |
| Slice thickness | False echoes in fluid | Elevational beam thickness |
| Speed error | Wrong depth | Speed differs from 1,540 m/s |
| Range ambiguity | Wrong depth | Echo assigned to wrong pulse |
| Aliasing | Wraparound | Doppler shift exceeds Nyquist |
| Spectral mirror | Duplicate waveform | Strong signal/excessive gain |
Common SPI Artifact Traps
Trap 1: Every dark region is shadowing
Not necessarily.
Consider anatomy, dropout, gain, and beam geometry.
Trap 2: Every bright posterior region is enhancement
Confirm that the beam passed through a low-attenuation structure.
Trap 3: Comet tail and ring-down are identical
Their appearance may overlap, but their physical mechanisms differ.
Trap 4: Aliasing is fixed by increasing gain
No.
Aliasing is fundamentally a sampling problem.
Trap 5: Mirror image means true duplicated anatomy
No.
Change the beam path and reassess.
Trap 6: False echoes in a cyst always mean pathology
Artifacts such as side lobes, beam width, and slice thickness can create pseudodebris.
Trap 7: Sound always travels exactly 1,540 m/s
The scanner assumes this value for soft tissue, but actual tissues vary.
Frequently Asked Questions
Are ultrasound artifacts tested on the SPI exam?
Yes. The current ARDMS SPI outline explicitly includes identifying and modifying scanning technique in response to gray-scale artifacts and places substantial emphasis on image optimization and Doppler concepts.
What is the most common ultrasound artifact to know for SPI?
There is no single artifact guaranteed to appear, but reverberation, shadowing, enhancement, mirror image, refraction, beam-related artifacts, and Doppler artifacts are all high-value concepts.
What causes reverberation?
Repeated reflection of sound between strong interfaces.
What causes posterior enhancement?
Low attenuation through a structure such as fluid allows relatively more sound to reach tissues behind it.
What causes mirror image artifact?
An indirect reflected sound path is interpreted by the system as though the sound traveled directly.
How do I tell side-lobe artifact from true debris?
Rescan in another plane or angle. Artifact echoes may change or disappear while true internal material remains anatomically consistent.
Why is artifact recognition important?
Because some artifacts hide anatomy, some imitate pathology, and others provide useful clues about tissue composition.
Key Takeaways
- SPI artifact questions are best solved using appearance → cause → correction.
- Reverberation creates repeated echoes from multiple reflections.
- Comet tail is a short reverberation-type artifact.
- Ring-down is associated with gas resonance.
- Shadowing occurs behind strongly attenuating structures.
- Enhancement occurs behind low-attenuation structures such as fluid.
- Mirror image duplicates anatomy across a strong reflector.
- Refraction can displace or duplicate anatomy.
- Beam-width, side-lobe, and slice-thickness artifacts can create false echoes in fluid.
- Speed error causes incorrect depth placement.
- Range ambiguity occurs when echoes are assigned to the wrong pulse.
- Not every artifact is undesirable.
- Changing the insonation angle or imaging plane is often one of the best ways to distinguish artifact from true anatomy.
Test Your SPI Artifact Knowledge
Do not memorize artifacts as isolated vocabulary words.
For every artifact, learn:
What does it look like?
Which physics principle caused it?
What would happen if I changed the beam, frequency, PRF, gain, or imaging angle?
That is the reasoning the SPI exam rewards.
Take our full SPI Practice Test to practice artifact recognition, Doppler, transducers, image optimization, ultrasound physics, and safety questions aligned with the current ARDMS blueprint.
