ACCURACY OF A VIDEO STRAIN-MEASUREMENT SYSTEM

The purpose of this study was to determine the accuracy of a video sys tem which our laboratory has been using to measure soft tissue strain. Both static and dynamic error analyses were performed to assess the a ccuracy of our video system. Static error was defined as the amount of movement reported by the video system for markers that were stationar y. Dynamic error was defined as the difference between the motion of t he markers as reported by the video system and their actual motion. Tw o sets of fluorescent markers were attached to a servo-hydraulic mater ials test machine. One marker set was attached to the hydraulic actuat or (moving markers) and the other set was attached to the base of the machine (stationary markers). Five different marker sizes, Eve camera distances, and seven different loading rates were studied. Results ind icated that the static error was independent of marker size, and that the dynamic error was independent of the loading rate and marker size for loading rates of 50% of the camera field of view (CFV) per second or slower. For loading rates greater than 50% of CFV per second, the m arker size did have an affect on the dynamic error. The mean static er ror was found to be 0.026% of CFV and the mean dynamic error was found to be 0.062% of CFV. (C) 1996 Elsevier Science Ltd.