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 experi-enced. 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 dy-namic US image interpretation, and higher probe frequency. These findings support the clinical utility of ultrahigh-frequency US for detailed evaluation of superficial nerves.
