Correction of Thickness Measurement by Ultrasound for Articular Cartilage Using Sound Velocity Estimation

Abstract

Background. Ultrasound measurement of osteoarthritis cartilage thickness is not sufficiently accurate if constant sound velocity is used. The aim of this study was to investigate the applicability of estimating the sound velocity using echo reflectance from the cartilage surface. Methods. Change in measurement error of cartilage thickness was evaluated using collagenase-treated osteochondral plugs. Sound velocity was calculated from the reflectance ratio, and the reference thickness was measured using a needle method. Findings. The relative errors of thickness measurements using constant sound velocity were increased after collagenase treatment. The errors using calculated sound velocity showed no significant difference between intact and degenerated samples. Interpretation. The collagenase treatment-induced error was reduced from 7% to 2% in absolute value, suggesting the applicability of the correction method for ultrasound measurement.