Validation of displacement measurements obtained from ultrasonic images during indentation testing

Biomechanical features of soft tissue are commonly investigated by indentation, a procedure where a blunt probe is advanced and the ensuing deformation of the tissue surface recorded. If it were possible to visualize subsurface anatomy during the indentation process, biomechanical investigation of internal tissue features might be feasible. The purpose of this experiment was to determine the accuracy of ultrasonically-derived measures of displacement obtained during indentation testing of an ultrasonic phantom. Using a 5-MHz sector transducer mounted to an automated indentation device, ultrasonic estimates of distance between a stationary target surface and the moving ultrasonic transducer were obtained and validated to a criterion. Depending on the method used to locate the target surface on the resulting B-mode image, the mean displacement error ranged from 14.37% to 22.05%. Use of this protocol for human tissue assessment, in vivo or otherwise, may be appropriate if the displacements of interest are greater than the error of the procedure.