Gas at abdominal US: appearance, relevance, and analysis of artifacts.
OBJECTIVE
To describe the spectrum of ultrasonographic (US) appearances of intraluminal gas, including two clinically relevant gas artifacts.


METHODS
Observations were made in patients and reproduced in an animal model, an ex vivo gut preparation, and a tissue-mimicking phantom. Appearances were classified according to a physical model of the interaction between sound and collections of gas.


RESULTS
Free bubbles of gas appeared as bright echogenic foci extending artifactually owing to lateral and axial blooming. This causes bubbles that abut the gut wall to enhance the layer one echo, which corresponds to the interface between the mucosa and the luminal contents. Such bubbles can also falsely appear to be within the gut wall itself owing to elevation averaging and thereby cause the artifact pseudo-pneumatosis intestinalis. Isolated groups of small bubbles created a characteristic periodicity and tapering of the distal echo pattern. In the extreme case, in which many such echoes are superimposed, "dirty shadowing" occurs. A contiguous pocket of gas may cause the gut wall to appear artifactually thickened (i.e., pseudo-thickened gut). This was shown to be a form of mirror image artifact.


CONCLUSIONS
Classification of the effects of gas on US images according to their physical characteristics may aid in their interpretation. Appreciating two previously undescribed artifacts, pseudo-pneumatosis intestinalis and pseudo-thickened gut, will improve the usefulness of abdominal US.
Wilson
S R
SR
Department of Medical Imaging, University of Toronto, Ontario, Canada.
Burns
P N
PN
Wilkinson
L M
LM
Simpson
D H
DH
Muradali
D
D
D000005:Abdomen / Q000000981:diagnostic imaging*; D000818:Animals; D016477:Artifacts; D004064:Digestive System / Q000000981:diagnostic imaging; D005740:Gases; D006801:Humans; D066298:In Vitro Techniques; D019047:Phantoms, Imaging; D011006:Pneumatosis Cystoides Intestinalis / Q000000981:diagnostic imaging; D013552:Swine; D014463:Ultrasonography
D005740:Gases