Detection of soft tissue foreign bodies in the presence of soft tissue gas.

Objective: To determine the effect of soft tissue gas on the accuracy of foreign body detection by realtime sonography.
Methods: This was a prospective randomized study using glass, metal, and bone inserted into turkey breasts to simulate human soft tissue foreign bodies. Air was subsequently injected around a random selection of the foreign bodies to simulate soft tissue gas that can accompany a blast or high-force injury. Using a linear transducer, physicians credentialed in the use of sonography were each asked to scan the breasts, identify the location of any foreign body, and describe whether the object located was bone, metal, or glass. They were also asked to describe the characteristics of the foreign body, including surface echogenicity, visibility, and artifacts, if any.
Results: The sensitivity for localization of each foreign body by each sonographer was 100% (48 of 48) and was unaffected by the presence of soft tissue gas. The accuracy of classifying the foreign body was poor except with bone. Glass and metal were often confused with each other. With the addition of soft tissue gas over the foreign bodies, the sensitivity of classifying the foreign body was decreased further from a combined 58% to 28%. The presence of soft tissue gas decreased the amount of reflection of the foreign body and obscured the subtle differences in the brightness of each foreign body, leading to a decrease in the accuracy of identification but not localization of the foreign body.
Conclusions: In an experimental model, soft tissue gas does not affect the localization of soft tissue foreign bodies. However, correct identification of the type of foreign body is limited by soft tissue gas because of loss of the typical sonographic characteristics.