Quantitative assessment of nerve echogenicity: comparison of methods for evaluating nerve echogenicity in ulnar...

The objective is to evaluate different methods to assess nerve echogenicity in a quantitative way by comparing a group of patients with ulnar neuropathy at the elbow (UNE) and a healthy control group, subsequently selecting the best tests for quantitative assessment of nerve echogenicity.

We included 56 patients with UNE and 37 healthy controls. High-resolution ultrasonography images of the ulnar nerve at the level of the medial epicondyle were saved in JPEG, TIFF or DICOM format, with a 19 pixels/mm resolution. Hypoechoic fraction was calculated by using 1 manual and 16 automatic thresholding methods.

A significant difference in mean hypoechoic fraction between patients and controls was found using the following automatic thresholding methods: MaxEntropy 82% versus 74% (p < 0.001), RenyiEntropy 80% versus 69% (p < 0.001), Shanbhag 76% versus 68% (p = 0.002), Triangle 45% versus 58% (p = 0.036) and Yen 79% versus 67% (p < 0.001). Of these five tests a significant correlation between hypoechoic fraction and the cross-sectional area was found for: MaxEntropy 0.542 (p < 0.001), RenyiEntropy 0.558 (p < 0.001), Shanbhag 0.219 (p = 0.035) and Yen 0.513 (p < 0.001). The manual thresholding method did not detect a significant difference in hypoechoic fraction between patients and controls, and inter-rater agreement in hypoechoic fraction for manual thresholding was poor.

Quantitative nerve echogenicity assessment can be successfully used to distinguish between a group of patients with UNE and a healthy control group, preferably by using the MaxEntropy, RenyiEntropy or Yen methods.

Automatic thresholding techniques using the MaxEntropy, RenyiEntropy or Yen methods are the best quantitative tests, and these quantitative measures can probably be used in further studies evaluating echogenicity in mono- and polyneuropathies.