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Purpose: To determine the smallest suture needles visible in post-operative abdominal radiographs of small, medium, and large patients, by correlating calculated suture needle detectability with radiologists’ detection confidence.
Methods: A suture needle phantom was constructed by arranging nine taper-style steel suture needles measuring from 5 mm to 13 mm in length in a 3x3 grid. Portable radiographs of the needle phantom were obtained within various thicknesses of soft tissue-equivalent material (Superflab bolus material, Mick Radio-Nuclear Instruments, Inc.) and an anthropomorphic phantom (Alderson phantom patient) following current post-op institutional imaging protocol. One board-certified abdominal radiologist with 30+ years of experience and three radiology residents assessed needle visibility on a diagnostic review monitor using a 4-point Likert scale (not visible, barely visible, visible, obviously visible). A template-matching observer model was implemented to compute suture needle detectability. Correlation between model observer performance and radiologist rankings were assessed using Kendall’s tau.
Results: Suture needle detectability decreased with increasing phantom thickness. 5 mm suture needles were not visible in any phantom image. In homogeneous phantom radiographs, suture needles of 8 mm, 9 mm, and 13 mm were visible at homogenous soft tissue-equivalent material thicknesses of 15cm, 22.5cm and 30cm, respectively. Suture needles 10 mm and larger were visible in anthropomorphic phantom images, even when obscured by under- or overlying bony structures. Radiologists’ assessment and model observer performance were correlated with a Kendall’s tau of 0.75.
Conclusion: Current Association of periOperative Registered Nurses (AORN) guidelines are based on suture needle size alone; however, this work suggests a post-operative imaging guideline based upon both patient- and suture-needle size would be more appropriate. Small patients may benefit from updated guidelines when very fine suture needles (below 10 mm) are suspected to be retained. Future work includes optimizing radiographic technique factors for patient size-specific retained suture needle detection.
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