Vet Detective · Ultrasound artefact teaching guide
Posterior Acoustic Shadowing & Enhancement
How relative attenuation creates darker or brighter tissue deep to a structure.
Animation paused. Compare Side-by-Side mode selected.
Outgoing illustrated wave packet
Returning illustrated echo
High-attenuation reflector: mineral example
Low-attenuation path: simple-fluid example
How to read the dots: In this simplified teaching illustration, dot size and brightness represent remaining relative pulse strength. All outgoing pulses start equal. The simple-fluid path loses less energy, so its dots remain larger than adjacent tissue paths at the same depth, but they never exceed their starting size. The size difference is deliberately exaggerated to make the comparison easy to see.
⬚ Physics View
The truth — what sound waves actually do
▣ B-Mode Image
What the machine renders on screen
Compare the two paths. In the mineral example, marked attenuation leaves less acoustic energy available to interrogate deeper tissue, so fewer echoes return from beyond the structure and a posterior shadow is displayed. In the simple-fluid example, the beam is attenuated less than through adjacent tissue. Echoes returning from tissue deep to the fluid are therefore stronger relative to neighbouring tissue at the same depth, producing posterior acoustic enhancement. The fluid does not add energy to the beam.
Clinical interpretation. Posterior shadowing and enhancement are useful image features, not standalone diagnoses. Shadowing supports marked attenuation from a strong reflector or absorber; enhancement supports lower attenuation along the beam path. Assess the structure itself, compare adjacent tissue at the same depth, scan in another plane and review the machine settings before drawing a conclusion.