Target displacement cased by tissue deformation is a major technical challenge in ultrasound-guided needle insertion for breast tumor treatment or biopsy. We previously developed a preloading-based needle insertion method, which consists of a preloading phase and an insertion phase, and validated its placement accuracy. The present study furthered this research by focusing on a new concave preloading probe to enhance needle insertion targeting. With this probe, we evaluated the several probe size for different tumor diameters and locations to investigate the geometry effect on insertion accuracy. In this in vitro study, preloading-based needle insertion with concave probe of the same diameter as that of the tumor showed the highest placement accuracy for shallow tumors, while concave probe of a larger diameter than that of the tumor showed the highest placement accuracy for deep tumors. Overall, the concave preloading probe described in this study decreased needle placement error. Future research focused on its evaluation by structural analysis based on soft tissue modelling and deformation simulation.
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