Evaluation of the effects of depth and frequency on foreign body detection in ultrasonographic imaging

Aim: Foreign bodies are defined as materials that penetrate the body from an external source and become lodged within tissues as a result of traumatic events. The detection and imaging of such foreign bodies are of significant importance for diagnosis and treatment. The aim of this study is to evaluate various foreign bodies of different sizes that may be present in the maxillofacial region in terms of echogenicity and artifacts on ultrasonographic (USG) images, and to investigate the effects of depth and frequency variations on size measurements in vitro. Material and Method: In this study, a total of 114 samples comprising ten different types of foreign bodies including glass, plastic, stone, graphite, wood, shotgun pellet, amalgam, composite, resin, and orthodontic wire were examined. The actual sizes of the foreign bodies were measured using a digital caliper. Subsequently, all samples were placed in agar agar superficially (10±2 mm) and deeply (30±2 mm) and examined with USG. Echogenicity and artifacts of the foreign bodies were assessed, and size measurements were performed separately at 7, 12 and 15 MHz frequencies. Measurements were compared using one-way ANOVA, and a Tukey post hoc test was performed when significant differences were observed. Agreement and systematic deviation (bias) were evaluated using Bland-Altman analysis (p<0.05). Results: All examined samples were imaged as hyperechoic on USG. In all foreign bodies, the mean sizes measured by USG were found to be higher than the mean actual sizes. A statistically significant difference between the actual size and the USG-measured sizes at different frequencies was observed only in the deeply seated stone and wood samples (p=0.001 and p=0.005, respectively). For the other foreign bodies, no significant differences were found between the actual and USG-measured sizes (p>0.05). When the effect of depth on size measurement was evaluated, a significant difference was found between the actual size of stone and wood specimens at all frequencies and the USG-measured size of deeply seated specimens (p<0.05). Conclusion: In this study, size measurements performed at different frequencies using the same probe revealed statistically significant differences only in deeply seated stone and wood samples. No significant differences were observed for other types of foreign bodies across frequencies. These findings suggest consistent measurement reliability, regardless of frequency differences in the same probe or the depth of foreign body localization, in most materials. Keywords: Agar agar, Bland-Altman, Ultrasonography, Foreign body