Image Optimization, Artifacts, and Contrast Echocardiography

Image Optimization Controls

Before interpretation, every 2D, M-mode, or Doppler image must be technically optimized. Five controls account for the great majority of routine adjustments:

Gain and TGC both affect brightness, but gain acts uniformly across the whole image while TGC acts selectively by depth — a frequently tested distinction. Adult transthoracic imaging typically uses a lower-frequency phased-array transducer than pediatric or vascular imaging because ultrasound must penetrate the chest wall and, often, lung to reach the heart; the frequency selected is always a deliberate trade-off, never simply "higher is always better."

Common Imaging Artifacts

An artifact is any structure appearing in the image that does not correspond to real anatomy, produced when an echo path violates an assumption the system uses to build its image — straight-line travel, constant propagation speed, and one reflection per pulse.

• Reverberation — sound bounces repeatedly back and forth between two strong, closely spaced reflectors (for example, the pericardium and an adjacent structure, or the two surfaces of a prosthetic valve) before finally returning to the transducer. Because the system assumes every returning echo came from a single reflection, each additional bounce is displayed as a separate, equally spaced band, producing a ladder of parallel bright lines extending to increasing depth.
• Acoustic shadowing — a strongly attenuating or highly reflective structure, such as dense calcification, a prosthetic valve, or a mechanical occluder disc, blocks most of the ultrasound energy from reaching structures directly behind it, producing an anechoic (dark) zone distal to the strong reflector. Shadowing can hide real pathology, such as a vegetation or thrombus, located behind a calcified annulus or prosthetic valve.
• Side-lobe artifact — a transducer's main beam is always accompanied by weaker, off-axis side lobes. When a side lobe strikes a strong reflector, the returning echo is displayed as though it originated from the main beam axis, misplacing it in the image. Side-lobe artifacts classically appear as spurious linear or punctate echoes projected into an otherwise echo-free space, such as false "smoke" or debris within the aorta or an atrial chamber.
• Mirror-image artifact — when the ultrasound beam encounters a strong, curved reflector (classically the diaphragm–lung interface), part of the beam reflects off that surface at an angle before continuing on to a true structure and back, so the system displays a duplicate, mirrored copy of the real structure at a false, deeper position equidistant beyond the strong reflector. This is a recognized pitfall in subcostal and apical views (duplicating cardiac structures beyond the diaphragm) and can also mimic a dissection flap in the descending thoracic aorta.

Contrast Echocardiography

Ultrasound-enhancing agents (UEAs) — Definity (perflutren lipid microsphere), Optison (perflutren protein-Type A microspheres with a human serum albumin shell), and Lumason (sulfur hexafluoride lipid-type A microspheres) — are gas-filled microbubbles small enough to pass through pulmonary capillaries and reach the left heart after peripheral IV injection. Combined with harmonic imaging, they are indicated primarily for left ventricular opacification and endocardial border definition when two or more contiguous LV segments are not adequately seen on unenhanced images, improving the accuracy of ejection fraction, wall-motion, and mass/thrombus assessment, and are also used to enhance Doppler and stress-echo endpoint detection.

Safety. Serious adverse reactions are rare but real. After post-marketing reports of a small number of deaths and cardiopulmonary reactions temporally associated with Definity/Optison administration, the FDA issued a boxed warning in 2007, later revised in 2008 to narrow the highest-risk population to patients with unstable cardiopulmonary conditions — recent acute coronary syndrome, worsening or decompensated heart failure, serious arrhythmias, respiratory failure, severe emphysema, pulmonary embolism, or other causes of pulmonary hypertension — who require cautious use and close monitoring. Anaphylactoid/anaphylactic reactions occur in only a very small fraction of administered doses; patients should be observed during administration and for at least 30 minutes afterward, with resuscitation equipment and trained personnel immediately available.

Contraindications are agent-specific and tied to composition:

A frequently misremembered point: known or suspected right-to-left, bidirectional, or transient right-to-left cardiac shunt is no longer an absolute contraindication for any of the three current agents. It was removed from the labeling of Optison, Lumason, and Definity between 2016 and 2017 after safety reviews found no scientific basis for the theoretical risk that microbubbles could bypass pulmonary filtration and enter the systemic circulation; it remains addressed today only as a warning/precaution regarding possible systemic embolization, not as a reason to withhold contrast.