Luka Pušnik, Natalie Winter, Maks Matej Cuzak, Igor Serša, Nejc Umek, Žiga Snoj, Gregor Omejec
PURPOSE: To determine the influence of evaluator experience, dynamic versus static ultrasound (US) image interpretation, and probe frequency on fascicle differentiation. METHODS: Evaluator experience and dynamic versus static US image interpretation were assessed on 12 cadaveric forearms. Median nerves were scanned using a 23-MHz US probe, followed by nerve excision and high-field magnetic resonance imaging (MRI) at 9.4-T. Five independent evaluators with different experience levels delineated fascicles twice, using static and dynamic US images. Delineations were compared with high-field MRI. The influence of probe frequency was evaluated on 12 median nerves of healthy volunteers. Median nerves at wrist were scanned using 14-, 18-, 24-, and 70-MHz US probes. Images were cross-referenced, and fascicle counts were compared relative to the highest-frequency probe. RESULTS: Dynamic imaging improved fascicle differentiation by 27.6% to 51.2% compared to static (P < .001), with a greater benefit for less experienced evaluators. The most experienced evaluator identified on average 62.3% more fascicles in dynamic assessment compared to the least experienced. The 70-MHz probe showed the highest mean fascicle count (27.6 ± 3.7), while 24-, 18-, and 14-MHz probes differentiated 26%, 46%, and 63% fewer fascicles, respectively (P <. 0001). CONCLUSIONS: Fascicle differentiation improves significantly with evaluator experience, using dynamic US image interpretation, and higher probe frequency. These findings support the clinical utility of ultrahigh-frequency US for detailed evaluation of superficial nerves. CLINICAL RELEVANCE: Experience and dynamic image interpretation are important for reliable fascicle recognition and to minimize misinterpretation. Ultrahigh-frequency US probes substantially improve fascicle differentiation, but their limited penetration requires careful selection of probe frequency based on nerve depth.