Ultrasound approaches to nerve imaging
Michal Byra, Ph.D.1, Jonathan Wong, B.S.1, Eric Hentzen, MD, PhD1, Michael Andre, Ph.D.1, Eric Y Chang, MD2 and Sameer B. Shah, PhD3, (1)UCSD, La Jolla, CA, (2)VA San Diego Medical Center, San Diego, CA, (3)Orthopedic surgery, UCSD, San Diego, CA
Carpal tunnel syndrome (CTS), resulting from median nerve compression at the wrist, is the most common entrapment neuropathy. The etiology of CTS neuropathy is variable, but manifests itself through both structural and biomechanical changes to the nerve and its surrounding environment. We investigated the use of high-frequency quantitative ultrasound to evaluate features related to median nerve echogenicity and shape, for carpal tunnel syndrome diagnosis (CTS). We recruited 10 patients with CTS and 21 healthy participants for this study. US images were collected using a 30 MHz probe (Vevo MD clinical ultrasound system) from median nerves at wrist in two configurations, with wrist extended and at rest. Various morphological features, including cross-sectional area (CSA), were calculated to assess nerve shape and contour complexity in each configuration. As CTS also may results in changes to nerve morphology as well as that of its surrounding environment, we developed the nerve-tissue contrast index (NTI) method; NTI is a ratio of average brightness levels of tissue and median nerve, both calculated based on US B-mode images. Finally, backscatter coefficient and several other quantitative ultrasound (QUS) parameters were calculated. Area under receiver operating characteristic curve (AUC) and t-test were used to assess the usefulness of the features for differentiation of patients with CTS from controls. For B-mode measurements, we obtained significant differences in the CSA and NTI parameters between the patients with CTS and controls (p-values<0.01), with the corresponding highest AUC values equal to 0.885 and 0.938, respectively. For the remaining morphological features, AUC values were below 0.685 and the differences in means between the patients and controls were not statistically significant (p-values>0.10). Wrist configuration had no impact on differences in average parameter values (p-values>0.09). Among quantitative parameters, backscatter coefficient differed between CTS patients and controls. Our study indicates that US may potentially provide useful information on structural components of even very small nerves (2x4 mm) and fascicles for diagnosing and monitoring injury, and surgical planning.
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