Which ultrasound artifact occurs when the slice thickness is wider than the structure being imaged?

• A. Partial volume artifact
• B. Mirror image artifact
• C. Shadowing
• D. Ring-down

Answer: (A)

The key idea is partial-volume artifact, which happens when the ultrasound beam’s elevational (slice) thickness is wider than the structure being imaged. In this situation, echoes from multiple tissues within a single slice are averaged together by the system, so the display represents a mix of signals rather than a single plane. This volume averaging blurs edges and can make a small structure appear with altered echogenicity or even seem smeared into surrounding tissue. It’s a masking effect from scanning a thicker slab than the structure occupies.

Other common artifacts come from different causes: mirror images arise from strong reflectors causing duplication, shadowing from highly attenuating material behind a structure, and ring-down from resonant gas bubbles. But the slice-thickness issue specifically leads to partial-volume averaging.