Diagnostic Performance of Shear Wave Elastography for Carpal Tunnel Syndrome Combined with High Frequency Ultrasound Imaging

Abstract

Ultrasound imaging has been investigated to aid the diagnosis of Carpal Tunnel Syndrome (CTS). The cross-sectional area (CSA), vascularity, and stiffness of median nerve (MN) have been suggested as diagnostic markers. Relative to the CSA, evaluation of vascularity and stiffness of the MN are more variable in their diagnostic performance. In this study, the diagnostic performance of MN stiffness from Shear Wave Elastography (SWE) at two sites and the vascularity from four different imaging techniques was compared. Additionally, a new criteria for MN stiffness evaluation, the stiffness ratio between MN and surrounding muscle was introduced and evaluated. SWE was acquired using an i18LX5 probe on an Aplio i800 system (Canon Medical Systems, Tustin, CA, USA) at the level of the wrist (site 1) and proximal to the pronator quadratus (site 2). Stiffness in the MN and surrounding muscle were quantified using a built-in software tool. The CSA and vascularity of MN were assessed at the wrist using an i24LX8 probe. Blood flow images were obtained using Color Doppler Imaging (CDI), Power Doppler Imaging (PDI), Monochrome and Color Superb Microvascular Imaging (mSMI and cSMI, respectively). The area of vascularity assessed by each technique was quantified offline by counting pixels of blood flow using Matlab (MathWorks, Natick, MA, USA). The diagnosis and severity of CTS was determined by clinical and electrodiagnostic tests. Diagnostic performance of the ultrasound features was assessed by t-tests, ANOVAs, and ROC analysis. The study included 20 control wrists and 26 CTS wrists. All ultrasound features were significantly different between the CTS and control wrists ( $\mathrm{p} ). The stiffness of MN at site 1 showed a higher accuracy than at site 2. The combination of CSA and MN stiffness ratio from site 2 showed an overall accuracy of 96% with a specificity and sensitivity of 95% and 92%, respectively. The CSA, MN stiffness from site 1 or 2, and CDI combination improved the diagnostic accuracy to 96% with specificity and sensitivity of 100% and 92%, respectively. SWE with high-frequency ultrasound imaging showed potential for the diagnosis of CTS, although no ultrasound feature differentiated all stages of CTS severity.