1. Accuracy and Reliability of Peripheral Nerve Diameter Measurement in Long Axis
Fadeel H. Mahmood1, Jeffrey A. Strakowski1,2, Marcie A. Bockbrader1, Daniel J. Kim1
Ohio State University, Columbus, OH, United States. 
Riverside Methodist Hospital and the McConnell Spine, Sport and Joint Center, Columbus, OH, United States. 
Introduction
Nerve Measurements
Results
Proximal
Distal
Expert and Novice diameter measurements (in cm) for distal and proximal ultrasound images
Distal Proximal
Nerve Model Expert Novice Expert Novice
Mean Mean (SE) 95% CI [LB,UB] Mean Mean (SE) 95% CI [LB,UB]
Median (0.036) [0.140, 0.325] (0.035) [0.171, 0.353]
(0.045) [0.184, 0.417] (0.065) [0.010, 0.344]
(0.005) [0.173, 0.198] (0.008) [0.142, 0.185]
Avg (0.026) [0.172, 0.307] (0.034) [0.114, 0.288]
Ulnar (0.017) [0.187, 0.273] (0.003) [0.170, 0.186]
(0.010) [0.196, 0.250] (0.020) [0.101, 0.204]
(0.009) [0.135, 0.182] (0.007) [0.138, 0.174]
Avg (0.011) [0.176, 0.231] (0.010) [0.137, 0.187]
Radial (0.004) [0.174, 0.195] (0.022) [0.173, 0.284]
(0.017) [0.195, 0.285] (0.013) [0.184, 0.250]
(0.016) [0.111, 0.193] (0.023) [0.149, 0.266]
Avg (0.011) [0.165, 0.220] (0.017) [0.173, 0.262]
Tibial (0.006) [0.228, 0.260] (0.012) [0.213, 0.274]
(0.030) [0.202, 0.354] (0.013) [0.255, 0.321]
(0.007) [0.156, 0.190] (0.021) [0.217, 0.324]
Avg (0.013) [0.197, 0.266] (0.012) [0.236, 0.298]
SE = Standard Error, CI = Confidence Interval, LB = Lower Bound, UB = Upper Bound 
Ultrasound is well-established as a complementary tool in the diagnosis of carpal tunnel syndrome as well as other entrapment neuropathies.
Although cadaver based studies confirm sonographic accuracy in describing peripheral nerve anatomy, more studies are needed to standardize measurement protocols.
Previous studies addressing neuropathy have utilized cross-sectional area (CSA) to assess pathology. Prior studies have shown good reliability and accuracy measurement of peripheral nerve CSA in short axis with recently trained examiners (Shoreman et al., Strakowski et al.).
Pathology should always be assessed in two planes during ultrasound evaluations, but this is frequently neglected with peripheral nerves. Our study was performed to evaluate accuracy and reliability of peripheral nerve measurement in long axis.
Median Nerve
Objective
Ulnar Nerve
Evaluate inter-rater and intra-rater reliability of peripheral nerve diameter measurement in the long axis by novice examiners.
Novice intra-rater reliability (Φ), inter-rater reliability (ρ^2), and precision (smallest detectable difference, SDD) for peripheral nerve diameter measurements
INTRA-RATER RELIABILITY INTER-RATER RELIABILITY SDD (cm)
Proximal Distal Proximal Distal Proximal Distal
Median Moderate Moderate Moderate Moderate
Ulnar Moderate Poor Moderate Good
Radial Good Poor Moderate Good
Tibial Moderate Poor Moderate Moderate
OVERALL Good Moderate Good Good
Methods
Design: Cross sectional study
Setting: Academic Medical Center
Participants:
IRB Approval: Ohio Health IRB #OH
Interventions:
Novice examiners completed two ultrasound training sessions
Our expert examiner obtained longitudinal ultrasound images of the radial, median, ulnar, and tibial nerves at proximal and distal sites for each healthy model
Novice examiners measured the diameter of each nerve at each site for each model three separate times (total of 72 measurements). The measurement order was randomized and all examiners were blinded to their numerical values. 
Main Outcome Measures:
Inter-rater reliability (generalizability coefficient - ρ^2)
intra-rater reliability (dependability coefficient - Φ)
Smallest detectable difference (SDD)
Ultrasound Observers
Observer
Experience 1
Novice 2 3 4 5 6 7
Expert
Healthy Nerve Models
Model
Age
Gender 1 29 F 2 M 3 30
Radial Nerve
Conclusions
Across all nerves and across all measurement sites intra-rater reliability was moderate (Φ=0.634) and inter-rater reliability was good (ρ^2 = 0.855), and precision (SDD) was 0.4 cm.
These coefficients varied by nerve and site. Across proximal and distal sites, the ulnar, tibial, and radial nerves all demonstrated good intra-rater reliability (Φ= 0.876, 0.844, respectively), inter-rater reliability (ρ^2=0.976, 0.958, respectively), and moderate precision (SDD =0.3, 0.4, 0.3 cm respectively). However, median nerve diameter measurements were not as reliable (intra- and inter-rater reliability: Φ=0.633 and ρ^2=0.698, respectively) or as precise (SDD = 1.0 cm).
Peripheral nerve diameter can be measured relatively reliably in the long axis with ultrasound by novice examiners with limited training. Further improvement in reliability could be reasonably expected with additional training.
Therefore, long axis diameter measurements should be incorporated into ultrasound training programs for use in the routine assessment of peripheral nerve size with high frequency ultrasound. 
Tibial Nerve
References
Shoreman, Strakowski, Bockbrader, Bradshaw, Mahmood, Tornero. “Accuracy and reliability of direct versus indirect peripheral nerve cross-sectional area” presented at American Institute for Ultrasound Medicine annual meeting in NYC, NY in March 2013. 
Strakowski, Shoreman, Bockbrader. “Accuracy and Reliability of Direct Peripheral Nerve Cross-Sectional Area Measurement with Comparison of the Indirect Method” presented at International Society of Peripheral Neurophysiological Imaging (ISPNI) annual meeting in Charleston, SC in May 2013.
Jeffrey Strakowski. Ultrasound Evaluation of Focal Neuropathies: Correlation with Electrodiagnosis. New York: Demos Medical Publishing, 2013.