Artifacts and the visualization of fetal distal extremities using three-dimensional ultrasound.

OBJECTIVES: To demonstrate that acoustic shadowing in 3D US may give rise to artifacts simulating limb defects and provide a solution to eliminate its occurrence. METHODS: Twenty second trimester fetuses (gestational age 15-24 weeks) were scanned with three-dimensional ultrasound (3D US) using a sagittal acquisition plane. Fetal tibia/fibula and radius/ulna pairs were assessed for completeness of imaging. A further 20 fetuses (gestational age 20-26 weeks) were scanned in both axial and sagittal planes and the results compared to verify clear visualization of both bones. RESULTS: Shadowing from adjacent structures produced an apparent limb defect in 55% of the first 20 fetuses imaged only sagittally (18% of limb pairs). Acquiring data from more than one orientation avoided this artifact. CONCLUSIONS: The 3D US is subject to the same artifacts as two-dimensional (2D US) in terms of acoustic shadowing, although their presentation may be different. Awareness of this fact is essential for correct interpretation of 3D US studies. Three-dimensional scanning protocols should be modified to ensure that fetal structures are adequately visualized by acquiring volume data in more than one acquisition orientation.