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Intervertebral disc, high-frequency ultrasound, strain, direct deformation estimation


High-resolution ultrasound imaging employs high-frequency sound waves that can be used to noninvasively visualize the structures within the body, facilitating medical diagnosis without the need for open surgery. The widespread utilization of ultrasound is attributed to its affordability, non-invasive characteristics, and use of non-ionizing radiation. Nevertheless, ultrasound is prone to artifacts originating from the surrounding environment, gas-liquid interfaces, or dense tissue. These artifacts are common in ultrasound images and can cause dropout, noise, and degraded resolution. In this study we analyzed intervertebral disc (IVD) strain during two axial compression testing cycles of bovine intervertebral discs with a 2-dimensional direct deformation estimation (2D-DDE) strain mapping approach. Currently, signal dropout and noise can inhibit accurate strain analysis. With electrical noise present in the images collected, we focused on reduction of the artifact present after acquisition. Specifically, ultrasound images were averaged across compression cycles to increase the signal-to-noise ratio. This improved the quality of the image and reduced strain dropout when conducting 2D-DDE strain analysis. Image artifacts caused less dropout when averaging ultrasound images across each cycle. These results suggest that the quality of IVD strain analysis from high frequency ultrasound could be improved by image averaging. Future work with additional animal and human studies where disc strain is quantified could help improve our understanding of the relationship between IVD loading and herniation.