POCUS Standoff: Comparing Ultrasound Interfaces for Soft Tissue Foreign Body Imaging.

Background: Point-of-care ultrasound can be used to identify foreign bodies (FBs) in soft tissue. Imaging interfaces such as standoff pads and water baths can improve image resolution for superficial soft tissue structures. Our objective was to determine the optimal interface for FB detection. We hypothesized that water baths would be associated with the greatest FB detection accuracy and image quality.

Methods: Prospective analysis of ultrasound imaging interfaces to detect FBs. 18 emergency physicians in training were enrolled: 8 interns, 8 senior residents, and 2 fellows. Four imaging interfaces were compared: gel, saline bag standoff, water bath, and a novel proposed interface: water-filled patient belongings bag (PBB). Standardized FBs (wood, plastic, and metal) were inserted into porcine models, which were imaged by participants using the interfaces. The primary outcome was the accuracy of FB detection for the interfaces. Secondary outcomes included time to FB detection, image quality, and impact of training level. Ultrasounds were reviewed by 2 blinded ultrasound fellowship-trained emergency physicians to determine FB visibility and image quality. Data analysis was performed using the χ2 test and Kruskal-Wallis test with GraphPad Prism Software.

Results: Eighteen participants completed 16 stations. Two hundred eighty-eight ultrasounds total. Interface types demonstrated a trend of greatest accuracy for PBB, followed by water bath, gel, and saline bag. Gel was significantly more accurate than saline bag (P=0.0120). Gel did not have a significant difference from PBB (P=0.1425) or water bath (P=0.125). As training level increased, time to FB detection significantly decreased (P=0.02), and accuracy increased. Accuracy for fellows was significantly greater than for senior residents (P=0.0473) and interns (P=0.0027). There was a trend of greater accuracy in senior residents from interns.However, there was no significant difference (P=0.0729).

Conclusions: PBBs may be a viable alternative interface for soft tissue FB detection. PBBs, water baths, and gel should be considered prior to saline standoffs.