📚 Guideline basis
AIUM/ASE equipment performance and artefact standards; ASE 2019 comprehensive TTE examination (JASE 2019;32:1–64); Porter TR, et al. Clinical applications of ultrasonic enhancing agents in echocardiography: 2018 ASE guidelines update (JASE 2018;31:241–74).
Why artefacts matter more in the ICU
Artefacts are not image degradation; they are structures that are not there, or real structures displayed in the wrong place. In an ambulatory laboratory an ambiguous finding is resolved by repositioning the patient and repeating the study the next day. In the ICU it prompts a thrombolytic, a sternotomy, or an escalation of care within the hour. The single discipline that prevents most artefact-driven errors is stated once here and repeated throughout the book:
Every suspected mass, flap, thrombus or vegetation must be confirmed in at least two orthogonal imaging planes, from more than one acoustic window, and must persist across a range of gain settings. An artefact fails at least one of these tests.
The artefact classes and their physics
Artefact | Physical mechanism | Appearance | Discriminating feature |
Reverberation | The pulse bounces repeatedly between two strong reflectors; each round trip is displayed deeper | Equally spaced parallel echoes at multiples of the true depth | Regular spacing; extends beyond anatomical boundaries; moves with the generating structure |
Comet tail / ring-down | Densely spaced reverberations from a small strong reflector | Bright tapering trail | Arises from a discrete point (calcification, lead, prosthesis) |
Mirror image | A strong specular reflector (diaphragm, pericardium) redirects the beam; the returning echo is displayed as if it lay beyond the reflector | A duplicate structure equidistant on the far side of the reflector | Perfect symmetry about the reflector |
Side lobe / grating lobe | Off-axis beam energy returns from a strong reflector and is displayed as if it lay on the main beam axis | A curved, arcing linear echo crossing a chamber cavity | Follows an arc at constant range; does not respect anatomy; disappears on rotation |
Acoustic shadowing | Near-field reflector or attenuator blocks the beam | Anechoic band deep to calcification, prosthesis, lead, rib, or air | Everything deep to it is uninterpretable, not normal |
Acoustic enhancement | Reduced attenuation through fluid | Brightening deep to a cyst or effusion | Expected behind fluid |
Refraction (Snell) | Beam deviates at an interface of differing propagation speed | Lateral displacement or duplication of a structure | Typically at fat–muscle interfaces; duplication of the aortic root is described |
Range ambiguity | In high-PRF, an echo from a deep structure returns after the next pulse and is displayed superficially | Structure displayed at the wrong depth | Occurs when high PRF is enabled |
Speed-of-sound displacement | Machine assumes 1540 m/s; fat is ≈1450, bone ≈3500 | Structures displaced deeper or shallower | Obese patients; the reason depth calibration drifts |
Near-field clutter | High-amplitude oscillation of the transducer face | Haze in the first 1–2 cm of the sector | Fixed to the near field, not the anatomy |
Doppler-specific artefacts
Artefact | Mechanism | Remedy |
Aliasing | Velocity exceeds the Nyquist limit (half the PRF) | Shift baseline, raise scale, reduce depth, lower transmit frequency, use CW (Chapter 4) |
Mirror-image spectral artefact | Strong reflection displays a symmetric envelope below the baseline | Reduce gain; recognise the symmetry |
Colour blooming | Excessive colour gain spills colour beyond the true jet | Reduce colour gain until speckle just disappears from tissue |
Ghosting / flash | Rapid tissue or transducer motion produces transient colour across the sector | Increase wall filter; recognise the transience |
Spectral broadening / "bearding" | Over-gained spectral display | Reduce gain; measure the dense modal envelope, not the outer spray — bearding inflates measured peak velocity |
The artefacts that mimic emergencies
These are the specific pattern-matches that generate wrong decisions in critical care.
Mimic | The artefact | How to disprove it |
Aortic dissection flap | Side-lobe or reverberation artefact from the posterior aortic wall or a calcified plaque | A true flap has independent motion out of phase with the aortic wall, interrupts colour flow, and persists in two planes. An artefact moves with the wall and colour crosses it freely |
Left atrial thrombus | Side-lobe artefact, or the coumadin ridge (the muscular ridge between the LA appendage and the left upper pulmonary vein) | The ridge has a characteristic location and a bulbous ("Q-tip") tip continuous with the wall; thrombus is discrete with a defined border |
Apical LV thrombus | Near-field clutter in a poorly visualised apex | Use an ultrasound enhancing agent — this is a guideline indication; contrast fills the cavity and outlines a true filling defect |
Vegetation on a lead or prosthesis | Reverberation and comet-tail artefact | Two orthogonal planes; TEE; consider CT/PET (Chapter 24) |
Pericardial effusion | The epicardial fat pad — hypoechoic, anterior, moves with the heart, often granular rather than anechoic | Effusion is dependent and circumferential in the supine patient; fat is anterior and does not layer posteriorly |
Pericardial vs pleural effusion | Both appear posterior to the heart in PLAX | The descending thoracic aorta is the landmark: pericardial fluid tracks anterior to it, pleural fluid extends posterior to it |
"Severe RV dilatation" | Off-axis, non-RV-focused apical view | Confirm in the RV-focused A4C, PSAX septal morphology, and subcostal (Chapter 9) |
Intracardiac mass | Prominent Eustachian valve, Chiari network, crista terminalis, moderator band, false tendon | All have stereotyped anatomical locations; recognise them rather than report them |
The ICU obstacle set
Obstacle | Physics | Response |
Positive-pressure ventilation with high PEEP | Hyperinflated lung interposes air between probe and heart; the heart is displaced caudally | Scan at end-expiration; go subcostal first; lower transmit frequency |
Subcutaneous emphysema | Total reflection at the air interface | Subcostal; suprasternal; TEE if the question is urgent |
Chest drains and dressings | Physical obstruction | Image around them; subcostal; TEE |
Post-sternotomy | Absent parasternal and apical windows; mediastinal air | TEE is the default (Chapter 36) |
Obesity | Attenuation proportional to path length | Lower frequency; left lateral positioning if permitted; ultrasound enhancing agent |
Cannot be positioned laterally (spine precautions, instability) | Loss of the best apical windows | Subcostal; TEE |
Prone position | Transthoracic imaging generally unobtainable | TEE via the standard route, described in ARDS cohorts (Chapter 27) |
Intra-aortic balloon pump, ECMO cannulae, pacing leads | Reverberation and shadowing | Multiple windows; TEE |
The single most useful manoeuvre in a difficult ventilated patient is not more gel and more pressure. It is: reduce transmit frequency, move to the subcostal window, and image at end-expiration. If that fails, escalate to TEE rather than repeating inadequate transthoracic attempts.
Optimisation sequence
A disciplined order, applied in seconds:
- Depth — structure of interest fills two-thirds of the sector
- Frequency/preset — drop frequency for penetration in obese or hyperinflated patients
- Gain — blood pool just black, myocardium grey. Over-gaining is the commonest self-inflicted error: it fills the cavity with speckle, blurs the endocardium outward, and causes systematic underestimation of LV volumes and overestimation of EF
- Time-gain compensation — correct near/far brightness mismatch; avoid slider-induced horizontal bands
- Focus — at the depth of the structure being measured
- Sector width — narrow to raise frame rate; check the frame rate on screen (below 40 Hz in a tachycardic patient means the settings are wrong)
- Dynamic range — narrow for endocardial border definition; widen to appreciate tissue texture
- Harmonics — on by default for border definition; off for measuring valve thickness, sizing a vegetation, and measuring LVOT diameter (Chapter 2)
Ultrasound enhancing agents
Aspect | Detail |
ASE indication | Two or more contiguous LV segments non-diagnostic on non-contrast imaging; also for suspected LV thrombus, apical variant HCM, and apical aneurysm |
Technique | Low mechanical index (typically 0.1–0.3); high MI destroys the microbubbles and produces a falsely opacified-then-empty ventricle |
Swirling artefact | Contrast destruction at excessive MI creates a swirling apical defect mimicking thrombus — reduce MI and re-image |
Attenuation artefact | Excessive contrast concentration shadows the basal segments — reduce dose or infusion rate |
Safety | Well tolerated in critical illness, with established safety in a large ICU and unstable-patient literature. Right-to-left shunt is a consideration but is not an absolute barrier in current guidance |
Value in the ICU | Converts a non-diagnostic study into a diagnostic one — frequently the difference between escalating to TEE and not |
Contrast is systematically under-used in critical care echocardiography. A poorly seen apex in a patient with an anterior infarct, or an unmeasurable endocardial border in a patient whose EF will determine inotrope therapy, is a direct indication.
🛑 Critical pitfall: Reporting a linear echo in the aorta as a dissection flap without demonstrating independent motion and colour flow interruption in two planes. Reverberation from the posterior aortic wall is the classic mimic, and the consequence of acting on it is a needless emergency transfer — or, worse, the opposite error of dismissing a true flap as artefact.
🛑 Critical pitfall: Over-gaining a poor image "to see better". It degrades every subsequent measurement and biases EF upward.
🛑 Critical pitfall: Treating everything deep to an acoustic shadow as normal. Shadowed tissue is unassessed, and the report must say so — this is the mechanism by which prosthetic mitral regurgitation is falsely excluded (Chapter 23).
- 💡 Clinical pearl: The descending aorta settles pericardial versus pleural effusion in one image: pericardial fluid tracks anterior to it, pleural fluid posterior.
- 💡 Clinical pearl: If a suspected finding disappears when you rotate the probe 90°, it was an artefact. Make the rotation reflexive before reporting any new mass.
- 💡 Clinical pearl: Reach for contrast earlier. Two non-diagnostic contiguous segments is a guideline indication, not a last resort, and it frequently avoids an invasive study.
References
- Mitchell C, Rahko PS, Blauwet LA, et al. Guidelines for performing a comprehensive transthoracic echocardiographic examination in adults. J Am Soc Echocardiogr 2019;32:1–64.
- Porter TR, Mulvagh SL, Abdelmoneim SS, et al. Clinical applications of ultrasonic enhancing agents in echocardiography: 2018 ASE guidelines update. J Am Soc Echocardiogr 2018;31:241–74.
- American Institute of Ultrasound in Medicine. Statements on equipment performance and bioeffects.
- Klein AL, Abbara S, Agler DA, et al. ASE recommendations for multimodality cardiovascular imaging of patients with pericardial disease. J Am Soc Echocardiogr 2013;26:965–1012.