Vet Detective · Ultrasound artefact teaching guide

Mirror Image Artefact

How a redirected pulse can return late and be displayed beyond a strong reflector.

SHOW:

Direct outgoing path

Direct returning echo

Reflected multi-segment path

Strong specular reflector

⬚ Physics View · Two Paths to One Target The reflected route is longer, so its echo returns later.

▣ B-Mode View · Displayed Echo Position In this model, the later echo is assigned a greater calculated depth.

Illustrated direct path

— units

Reference path; not a physical measurement

Illustrated reflected path

— units

Probe → reflector → target → reflector → probe

Illustrated ghost depth

— units

Calculated from reflected round-trip time

Relative path difference

—%

Reflected versus direct

Compare the two paths. The cyan packet follows the direct route to the illustrated target and back. The purple packet follows a longer, multi-segment route involving the strong reflector and the same target. Its echo therefore returns later. Because the imaging system assumes a straight path and a single round trip, it assigns the later echo a greater calculated depth and displays an artefactual copy beyond the reflector.

Clinical interpretation. A mirror image artefact represents misplaced information from real anatomy; it is not an additional structure. A familiar veterinary example is the gallbladder and surrounding liver displayed beyond the diaphragm in a subxiphoid or cranial abdominal view. The duplicated image may resemble the true structure but can be weaker or distorted. Confirm unexpected anatomy in another imaging plane before diagnosing thoracic pathology or diaphragmatic disruption.

How to test the appearance. Change the imaging plane or beam angle so the strong reflector is no longer in the same path. A mirror image may shift, weaken or disappear, while the real anatomy remains anatomically consistent across views. Review gain and confirm the finding with a complete examination rather than relying on a single image.