Usg artifacts
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This document discusses various types of artifacts that can appear on ultrasound images and their causes. It describes artifacts such as reverberation caused by parallel reflective surfaces, ring-down artifacts appearing behind gas collections due to resonant vibrations, comet-tail artifacts caused by multiple closely spaced reflections from structures like surgical clips, and shadowing caused by attenuation from structures like calcifications. It also discusses artifacts that can appear on Doppler ultrasound images including aliasing from very high velocities, mirror images from signal leakage, and flash artifacts from probe or body motion. Prevention techniques are provided for some artifacts.
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Usg artifacts
- 1. ULTRASOUND - ARTIFACTS Dr Saket Jain 3rd year resident MGM HOSPITAL
- 2. ARTIFACTS - GRAY-SCALE • are echoes that appear on the image but do not have a true correspondence to an anatomical structure
- 3. REVERBERATION • Appearance- Multiple equidistantly spaced linear reflections , ladder • Physics - parallel highly reflective surfaces, the echoes generated from a primary US beam may be repeatedly reflected back and forth before returning to the transducer for detection • Prevention – decrease TGC near in the near gain Change beam angle / alternative window
- 4. RING-DOWN ARTIFACT • Appearance - A line or series of parallel bands extending posterior to a gas collection • Physics - US energy causes resonant vibrations of the air bubbles • Occurs - Posterior to collections of gas (eg, pneumobilia, portal venous gas, gas in abscesses, bowel).
- 5. COMET-TAIL ARTIFACT • Appearance - Series of multiple, closely spaced small bands of echoes . • Physics - is a form of reverberation , two reflective interfaces and thus sequential echoes are closely spaced that individual signals are not perceivable in the image . • Occurs - surgical clips. copper intrauterine device • Prevention – decrease TGC near in the near gain Change beam angle / alternative window
- 6. SHADOWING • Appearance - Dark or hypoechoic band deep to a highly attenuating structure , clean shadowing • Physics - US beam encounters a tissue that attenuates the sound to a greater or lesser extent than in the surrounding tissue, the strength of the beam distal to this structure will be either weaker or stronger than in the surrounding field. • Occurs - Calcified lesions, dense tumors • Prevention - Image structure in different angles
- 7. DIRTY SHADOWING • Appearance - Low-level echoes in the shadow deep to gas • Physics - due to the high degree of reflection at gas/tissue interfaces
- 8. INCREASED THROUGH-TRANSMISSION / ENHANCEMENT • Appearance - Hyperechoic area behind a structure • Physics - Fluid-containing structures attenuate the sound much less than solid structures • Occurs - Behind fluid-filled structures and occasionally behind solid lesions that attenuate sound less than surrounding tissue (eg, fibroadenoma). • Prevention – Reduced with spatial compounding different direction
- 9. “GHOSTING” • Appearance - Duplication of a structure or structures appearing wider on the US image • Physics - speed of sound varies in different tissues – fat < fliud < ST . • Sound is refracted & degree of this change in direction is dependent on both the angle of the incident US beam and the difference in velocity between the two media • Prevention – angle change
- 10. REFRACTIVE SHADOWING (EDGE ARTIFACT, LATERAL CYSTIC SHADOWING) • Appearance - Shadow occurring at the edge of a curved surface • Physics - Sound waves encountering a cyst wall or a curved surface at a tangential angle are scattered and refracted . • Occurs - Cysts, urinary bladder (appearance of a defect in the bladder wall), diaphragm if there is fluid on either side (appearance of a defect in the diaphragm). • Prevention - disappear when changing the angle
- 11. SIDE LOBES AND GRATING LOBE ARTIFACTS • Appearance - Hyperechoic rounded object within an anechoic or hypoechoic structure - urinary bladder or gallbladder lumen • Physics - In linear array transducers, multiple other low-amplitude beams project radially at different angles away from the main-beam axis. These are termed side lobes. • Occurs - Urinary bladder, gallbladder, needle biopsy • Grating lobe artifacts are reduced by using very closely spaced elements in the array
- 13. VOLUME AVERAGING (SECTION THICKNESS, SLICE THICKNESS) • Appearance - False sludge or debris within anechoic cystic structures • Physics - As the beam propagates away from the transducer, it narrows gradually until it reaches the focal zone. It then gradually widens again. • minimized by placing the focal zone at the level of the tissue • Occurs - Urinary bladder, gallbladder, and cysts
- 14. MIRROR-IMAGE ARTIFACT • Appearance - Duplicated structure equidistant from a strongly reflective interface • Physics - The return of sound beams is delayed, and therefore the structures from which these delayed beams are reflected are displayed at a greater depth than their true anatomic depth • Occurs - Diaphragm with liver lesions or the liver itself being duplicated. • Prevention – scan from different angle , adjust focal zone or TGC at the level of the diaphragm , scan from multiple windows
- 15. ELECTRONIC INTERFERENCE/SPIKING • Appearance - Bands of noise • Physics - This can occur when there is not a dedicated electrical outlet that is appropriately grounded
- 16. SPECKLE • Appearance - The random granular texture that obscures anatomy in US images (noise) • Physics - complex interference of US echoes made by reflectors spaced closer together than the US system’s resolution limit . • Reduced using techniques that reduce noise (i.e, higher-frequency transducer, real-time compounding, adaptive post-processing, and harmonic imaging
- 17. ANISOTROPY • Appearance - Hypoechoic area in a structure • Physics - transducer’s angle of incidence is not perpendicular to the structure • Occurs - Tendons, and to a lesser extent muscles, ligaments, and nerves.
- 18. SPECTRAL & DOPPLER ARTIFACTS
- 19. ALIASING • Appearance – blood flow direction appears to be reversed & on waveforms, the high-frequency component is wrapped around to the negative extreme • Physics - when the velocity of the sampled object is too great for the Doppler frequency to be determined by the system. • Diminished or eliminated by increasing the PRF , increasing the velocity scale (which increases the PRF), increasing the Doppler angle (which decreases Doppler shift), changing the baseline setting, or using a lower US frequency
- 20. MIRROR IMAGE (CROSS TALK) • Appearance - Mirror image of the spectral display on the opposite side of the baseline. • Physics - When a strong sound signal in one direction channel leaks into another. • Occurs - Equipment malfunction & Doppler gain too high , Doppler angle close to 90. • Prevention – Change angle
- 21. TISSUE VIBRATION Appearance - Red and blue Doppler signal in perivascular soft tissue Physics – turbulence = fluctuation in lumen = vibration of vessel wall & adjacent ST • Occurs - Arteriovenous fistulas and shunts
- 22. TWINKLE Appearance - discrete focus of alternating colors behind a echogenic object Physics - dependent on US machine settings motion of the object scanned with respect to the transducer, and equipment used.
- 23. FLASH ARTIFACT • Appearance - Spurious appearance of blood flow • Physics - motion of the patient’s body, motion of the probe, or motion of an anatomic structure secondary to an external force • Prevention - motion discriminator function that can be found in most US machines
- 24. VASCULAR MOTION ARTIFACT • Appearance - Artifactual increase and decrease of spectral Doppler velocity pattern in a cyclical fashion • Physics – cyclical motion of liver due to heart • Occurs - Hepatic vessels.
- 25. SPURIOUS THROMBOSIS RELATED TO VELOCITY SCALE, WALL FILTER, AND GAIN • Appearance - Spurious thrombosis • Physics - Result of setting the velocity scale or wall filter too high or the gain too low . occurs - Veins.
- 26. INCORRECT COLOR STEERING/ANGLE Appearance – color may not present where flow exists Physics - Angle to flow closer to 0 or 180 degrees and not close to 90 degrees
- 27. OVERGAINING COLOR • Appearance – bleeding over in non flow regions
- 28. 3-D ULTRASOUND ARTIFACT • PHYSICS – Motion or vibration of the targeted organ • Shadowing from adjacent organ
- 29. THANK YOU
Editor's Notes
- sound travels in a straight line and at a constant speed, the only source of sound is the transducer, that sound is attenuated uniformly throughout the scan plane, each reflector in the body will only produce one echo, and the thickness of the slice is assumed to be infinitely thin. When these assumptions are not accurate, artifacts are produced
- US image algorithm assumes that an echo returns to the transducer after a single reflection and that the depth of an object is related to the time for this round trip -- The echo that returns to the transducer after a single reflection will be displayed in the proper location. The sequential echoes will take longer to return to the transducer, and the US processor will erroneously place the delayed echoes at an increased distance from the transducer
- vibrations create a continuous sound wave that is transmitted back to the transducer. This phenomenon is displayed as a line or series of parallel bands extending posterior to a gas collection adenomyomatosis
- The later echoes may have decreased amplitude secondary to attenuation; this decreased amplitude is displayed as decreased width
- US beam encounters a strongly attenuating or highly reflective structure, the amplitude of the beam distal to this structure is diminished
- energy of a sound pulse reflected off same as the transmitted pulse, the reflected pulse will interact with the interfaces in front of the gas and produce secondary reflections that travel back to the gas surface and then reflect from this surface back to the transducer. These secondary reflections produce low-level echoes in the shadow deep to the gas, accounting for the “dirty” appearance.
- ,strength of the sound pulse is greater after passing through fluid interfaces deep to cystic structures will produce stronger reflections and appear brighter than identical interfaces deep to solid tissue
- Occurs - interface between the rectus abdominis muscles and abdominal wall adipose tissue; at the interface between liver or spleen and adjacent adipose tissues Refraction artifact may cause structures to appear wider than they actually are or may cause an apparent duplication of structures
- The result is a lack of echoes returning from the lateral cyst wall and anything in a direct path posterior to it. This has an appearance of a linear shadow.
- Side-lobe and grating lobe beams may be reflected back transducer/machine cannot differentiate between reflected beams returning from the main beam versus those return-ing from off-axis lobes Off-axis lobes are lower in amplitude than the main axis beam, and therefore in order to be detected by the transducer, they must be reflected by a highly reflective (ie, highly echogenic) structure
- Structures that are proximal to and distal from the focal zone are more prone to artifacts resulting from volume averaging between adjacent objects that both fall within the thickness of the beam
- This delay occurs in the presence of highly reflective interfaces, such as the diaphragm/lung base interface on a right upper quadrant scan A pulse from the main beam travels through the liver and is reflected off the diaphragm. This reflected echo reaches the liver lesion and reflects back to the diaphragm.14 From the diaphragm, the echo finally reaches the transducer.
- If a non-dedicated electrical outlet is used and another piece of equipment is turned on, electric signals may enter the US machine
- Speckle interferes with the ability of a US system to detect low-contrast objects
- When a tendon (highly anisotropic) is imaged perpendicular to the US beam, a characteristic hyperechoic fibrillar appear-ance is displayed
- A minimum of two pulses per cycle of Doppler shift frequency is required to determine the corresponding velocity.When there is an insufficient PRF relative to the Doppler signals generated by moving blood, aliased signals occur gives the false appearance of reversal of flow within the vessel
- in bi-directional Doppler systems has a forward channel (I channel) and a reverse channel (Q channel) so that forward flow can be differentiated from reverse flow. If some of a true signal “leaks” into the reverse channel, an artificial signal is presented reflected across the baseline
- vibration artifact is produced in nonflow areas by bruits, arteriovenous fistulas, and shunts The vibrational motion is both towards and away from the transducer, resulting in a color-assignment mixture or red and blue
- (color, gray-scale gain, and PRF), there is a strong reflector with a rough surface, these slight variations in beam direction could be magnified to produce apparent aliased Doppler shifts. Multiple reverberations would further magnify this effect by projecting the artifact below the reflecting surface.
- The motion of the reflectors results in a Doppler shift, giving a spurious appearance of blood flow.
- The vessel thus moves in relation to the fixed location of the sampling box. This results in sampling of a continuum of locations within the cross section of the blood vessel. As the sample box interrogates toward the periphery and back toward the center, the spectral Doppler velocity pattern will artifactually decrease and increase in a cyclical fashion
- wall filter is used to remove high-amplitude low-frequency Doppler shifts caused by reflection from the slowly moving vessel wall.
- Color Doppler is angle dependent changed by either manually rocking the transducer or using a different imaging window the angle approaches 90 degrees, no Doppler shift is detected and.
- Once color is presented, increasing the color gain potentially will cause very little change in the color image until the gain is high enough that the noise floor signals are amplified above the threshold & color noise speckle becomes apparent in the image appreciated by color presentation bleeding over in non-flow regions
- for example, an apparent limb defect or cleft lip and palate