PHYSICS 2 ARTIFACTS ✅

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TERM / DEFINITION FLASHCARDS

Ultrasound Artifacts — Core Concepts

Artifact An echo that does NOT represent real anatomy; can appear as structures that aren't real, missing anatomy, wrong location/depth, or wrong brightness/shape; key clue = disappears when you change angle or imaging plane

Machine Assumptions (that cause artifacts when violated) Sound travels in a straight line; speed = 1540 m/s (1.54 mm/µs); echoes come from the beam axis only; reflection strength equals tissue characteristics; imaging plane is infinitely thin

Dual Nature of Artifacts Artifacts can mislead diagnosis (bad) OR help confirm diagnoses (good); shadowing helps detect stones; enhancement confirms fluid-filled structures

Artifact Classification (4 types) Propagation artifacts, attenuation artifacts, resolution artifacts, Doppler artifacts

Resolution Artifacts

Axial Resolution Artifact Occurs when two reflectors are closer together than SPL/2 (half the spatial pulse length); they appear as ONE structure instead of two; reflectors must be parallel to the beam axis; fix = use higher frequency transducer (shorter SPL)

SPL (Spatial Pulse Length) Number of cycles × wavelength; determines axial resolution; shorter SPL = better axial resolution = fewer axial artifacts; improved by using higher frequency

Lateral Resolution Artifact Occurs when two reflectors are closer together than the beam width; they appear merged into one structure; reflectors must be perpendicular to the beam axis; fix = narrow beam, proper focal zone, higher frequency

Elevational Resolution Artifact (Slice Thickness / Section Thickness / Partial Volume / Edge Wall Artifact) Caused by beam thickness in the elevation plane; adds false echoes inside structures — example: cyst appears to contain debris when it doesn't; fix = harmonic imaging (narrower beam), 1.5D arrays, disc-shaped elements

Contrast Resolution Ability to distinguish different shades of gray; improved by increasing bit depth/gray scale or using B-scale; artifacts occur when gray shade differences are too subtle to display

Spatial Resolution (Overall) Combined image detail from pixel density, line density, and display monitor lines; improved by write magnification; pixel density itself cannot be changed by the operator

Propagation Artifacts

Speckle Grainy "salt and pepper" noise throughout the image; caused by small amplitude sound waves interfering with each other; fix = harmonic imaging

Refraction Beam bends at a tissue interface → produces a duplicate side-by-side image of a structure; fix = change transducer angle

Mirror Image Artifact A duplicate of a real structure appears deeper than the actual structure; caused by a strong reflector (most commonly the diaphragm); fix = change angle or adjust gain

Multipath Artifact Sound beam takes multiple different paths back to the transducer; causes echoes to appear at the wrong depth; machine assumes single straight-line path

Reverberation Artifact Sound bounces repeatedly between two strong reflectors; produces evenly spaced lines (ladder pattern or Venetian blind pattern); only the first echoes are real; fix = use alternative acoustic window, decrease near-field TGC, change angle

Comet Tail Artifact A type of reverberation; short, tapering posterior echoes; caused by metal or cholesterol crystals; distinguishing feature = tapers and shortens with depth

Ring Down Artifact A type of reverberation; long echoes that expand or continue posteriorly; caused by gas bubbles; distinguishing feature = continues and expands rather than tapering

Propagation Speed Error (Range Error) Occurs when tissue speed differs from the assumed 1540 m/s; faster medium → structure appears too shallow; slower medium → structure appears too deep; currently cannot be prevented; fix = use alternate viewing window or change beam angle

Focal Banding Increased image intensity caused by multiple focal zones creating overlapping areas of brightness; fix = decrease number of foci or change foci location

Side Lobes False echoes outside the main beam produced by a single-element transducer; create artifactual echoes inside fluid-filled structures like cysts or bladder

Grating Lobes False echoes outside the main beam produced by array transducers (multiple elements); similar effect to side lobes but specific to arrays; fix = apodization or subdicing

Apodization Technique to reduce side lobes and grating lobes; excites center elements with higher voltages and outer elements with weaker voltages; strengthens main beam and reduces off-axis artifacts

Subdicing Process of cutting a single transducer element into many smaller sub-elements; sub-elements are individually wired but fire together as one unit; helps reduce grating lobes

Attenuation Artifacts

Shadowing Dark area posterior to a strongly attenuating or reflecting structure; structure blocks sound from reaching deeper tissues; two types = clean and dirty; very important clinically

Clean Shadowing Dark anechoic shadow posterior to a highly reflective smooth interface; produced by stones (gallstones, kidney stones, calcified arteries); shadow has sharp, clear edges

Dirty Shadowing Cloudy or echogenic shadow posterior to a structure; produced by gas; less well-defined than clean shadowing

Enhancement (Posterior Acoustic Enhancement) Bright area posterior to a weakly attenuating structure; machine assumes all tissue attenuates equally — fluid attenuates less, so deeper echoes appear brighter; confirms fluid-filled structures like cysts and bladder

Doppler Artifacts

Aliasing Most common Doppler artifact; occurs when blood flow velocity exceeds the Nyquist limit (PRF ÷ 2); waveform appears reversed or wrapped around baseline on spectral display; first step to fix = adjust baseline; other fixes = increase PRF, lower baseline, use CW Doppler

Nyquist Limit Maximum measurable Doppler shift before aliasing occurs; = PRF ÷ 2; exceeded = aliasing; fix by increasing PRF to raise the Nyquist limit

HPRF (High Pulse Repetition Frequency) Doppler Special mode of PW Doppler using multiple sample volumes along the same scan line; allows higher PRF than normal PW; main goal = reduce aliasing; can measure faster velocities than regular PW Doppler

Crosstalk Mirror image of the spectral Doppler waveform appearing on the opposite side of the baseline; caused by Doppler gain set too high or beam angle close to perpendicular (90°)

Range Ambiguity PRF set too high → next pulse sent before previous echoes return → echoes appear to come from wrong depth; specific to PW Doppler; CW Doppler has no range resolution so it cannot have range ambiguity

Ghosting (Clutter) Low-frequency Doppler shifts caused by slow-moving tissue and vessel walls rather than blood; appears as noise near the baseline; fix = wall filter

Twinkle Artifact Rapidly changing color signal appearing posterior to a strong scatterer (like a kidney stone or calcification); helps detect stones; appears as rapid color flickering behind the reflector

Flash Artifact Sudden burst of false color throughout the image caused by probe or patient motion; not related to actual blood flow

Wall Filter Removes low-frequency Doppler signals from slow-moving tissue and vessel walls (ghosting/clutter); if set too high, eliminates real slow-flow signals

Q&A FLASHCARDS

Core Artifact Concepts

Q: What is an artifact and what is the key clinical clue that something is an artifact? A: An echo that does not represent real anatomy; key clue = it disappears or changes when you change the transducer angle or imaging plane

Q: What are the 4 main machine assumptions that, when violated, produce artifacts? A: Sound travels in a straight line; speed = 1540 m/s; echoes come only from the beam axis; reflection strength = tissue characteristics; imaging plane is infinitely thin

Q: Can artifacts ever be useful clinically? A: Yes — shadowing detects gallstones/kidney stones; enhancement confirms fluid-filled structures (cysts, bladder); twinkle artifact helps detect stones

Q: What are the 4 categories of ultrasound artifacts? A: Propagation artifacts, attenuation artifacts, resolution artifacts, Doppler artifacts

Resolution Artifacts Q&A

Q: When does an axial resolution artifact occur and how do you fix it? A: When two reflectors are closer together than SPL/2 and parallel to the beam; they merge into one; fix = use higher frequency transducer to shorten SPL

Q: When does a lateral resolution artifact occur and how do you fix it? A: When two reflectors are closer together than the beam width and perpendicular to the beam; they merge; fix = narrow beam, proper focal zone, higher frequency

Q: What causes the slice thickness (elevational) artifact and what is the classic example? A: Beam thickness in the elevation plane adds false echoes from outside the imaging plane into the image; classic example = a simple cyst appears to contain internal debris (pseudodebris) when it is actually anechoic

Q: How do you fix the slice thickness artifact? A: Use harmonic imaging (produces narrower beam); use 1.5D arrays or disc-shaped elements that produce thinner slices in the elevation plane

Q: What is the difference between axial and lateral resolution artifacts in terms of reflector orientation? A: Axial resolution artifact = reflectors parallel to the beam; lateral resolution artifact = reflectors perpendicular to the beam

Propagation Artifacts Q&A

Q: What causes speckle and how do you reduce it? A: Small amplitude sound waves interfere with each other producing grainy "salt and pepper" noise; fix = harmonic imaging

Q: What is the mirror image artifact and what commonly causes it? A: A duplicate of a real structure appears at a greater depth than the actual structure; most commonly caused by the diaphragm acting as a strong reflector

Q: What is the difference between comet tail and ring down artifacts? A: Both are reverberation types; comet tail = short, tapering echoes caused by metal or cholesterol; ring down = long, expanding echoes caused by gas bubbles

Q: What does a reverberation artifact look like and what causes it? A: Evenly spaced parallel lines (ladder pattern or Venetian blind pattern) deeper in the image; caused by sound bouncing repeatedly between two strong reflectors; only the first echoes are real

Q: How do you fix a reverberation artifact? A: Use an alternative acoustic window; decrease near-field TGC; change transducer angle

Q: What happens with propagation speed error and in which direction does the error go? A: If tissue speed is faster than 1540 m/s → structure appears too shallow; if tissue speed is slower → structure appears too deep; cannot currently be prevented

Q: What causes focal banding and how do you fix it? A: Multiple focal zones create overlapping areas of increased intensity; fix = decrease the number of foci or change foci locations

Q: What is the difference between side lobes and grating lobes? A: Side lobes = produced by single-element transducers; grating lobes = produced by array transducers (multiple elements); both create false echoes outside the main beam; fixed by apodization and subdicing

Q: What is apodization and what does it fix? A: Excites center elements with higher voltages and outer elements with weaker voltages; reduces side lobes and grating lobes; strengthens the main beam

Q: What is subdicing? A: Cutting a single transducer element into many smaller sub-elements; sub-elements are individually wired but fire together as one unit; reduces grating lobes

Q: What is refraction and what does it produce on the image? A: Beam bends at a curved tissue interface; produces a side-by-side duplicate of a structure; fix = change transducer angle

Attenuation Artifacts Q&A

Q: What is the difference between clean and dirty shadowing? A: Clean shadowing = sharp, anechoic (dark) shadow produced by stones (gallstones, kidney stones); dirty shadowing = cloudy, echogenic shadow produced by gas

Q: What machine assumption does posterior acoustic enhancement violate? A: The assumption that reflection strength is related only to tissue characteristics; fluid attenuates less than assumed, so tissues behind it receive more sound energy and appear brighter than they should

Q: What structures produce posterior acoustic enhancement? A: Fluid-filled structures — cysts, bladder, gallbladder (when no stones), any anechoic structure

Q: Why is shadowing clinically important? A: It helps detect highly reflective or attenuating structures — gallstones, kidney stones, calcified arteries; the presence of clean shadowing strongly suggests calcification or stone

Doppler Artifacts Q&A

Q: What is the most common Doppler artifact and what causes it? A: Aliasing; occurs when blood flow velocity exceeds the Nyquist limit (PRF ÷ 2); waveform appears wrapped around or reversed on spectral display

Q: What is the first step to fix aliasing in spectral Doppler? A: Adjust/shift the baseline; then increase PRF (scale); can also lower transducer frequency, decrease depth, or switch to CW Doppler

Q: What is HPRF Doppler and why is it used? A: High Pulse Repetition Frequency Doppler — a special PW Doppler mode using multiple sample volumes along the same scan line; allows higher PRF to raise the Nyquist limit; used to measure faster velocities while maintaining some depth information

Q: What causes crosstalk and what does it look like? A: Doppler gain set too high or beam angle close to 90°; produces a mirror image of the spectral waveform duplicated on the opposite side of the baseline

Q: What is range ambiguity and when does it occur? A: PRF set too high → next pulse transmitted before all echoes from the previous pulse return → echoes appear at the wrong depth; specific to PW Doppler

Q: What is ghosting (clutter) and how do you fix it? A: Low-frequency Doppler signals from slow-moving tissue and vessel walls rather than blood flow; appears as noise near baseline; fix = increase wall filter setting

Q: What is the twinkle artifact and why is it useful? A: Rapid flickering color signal posterior to a strong scatterer like a kidney stone; helps detect stones that might otherwise be hard to see; caused by multiple strong scatterers

Q: What causes flash artifact? A: Sudden probe or patient motion during color Doppler scanning; produces a burst of false color across the image unrelated to actual blood flow

Q: What happens if the wall filter is set too high? A: Real slow-flow blood signals near the baseline are eliminated along with the tissue noise; leads to missing clinically important low-velocity flow

Q: What is the key difference between aliasing and range ambiguity as Doppler artifacts? A: Aliasing = PRF too LOW → Nyquist exceeded → velocity appears wrong/reversed; range ambiguity = PRF too HIGH → echoes return after next pulse sent → depth appears wrong

Total card count: 38 term/definition cards + 27 Q&A cards = 65 flashcards covering all artifact types. Copy and paste wherever you need!