Abstract: A method is provided for measuring soft tissue deformation based on the image morphology
in order to obtain the amount of tissue deformation during needle insertion procedure accurately. The
algorithms of edge detection, image expansion and corrosion are explained and employed to enhance
the images of the markers embedded into soft tissue. The centroids of the markers are extracted and
stored into the measurement matrix M. A measurement platform, including the precision motion stage,
industrial camera, light source and crystal artificial tissue with marker, is built. The real-time images are
collected during needle insertion procedure. The displacements of the markers are calculated using the
morphology-based method. The measurement error is less than 0.7 mm with the compensation. The
method could improve the accuracy and precision of robot-assisted needle insertion surgeries.

Key words: soft tissue, needle insertion, tissue deformation, morphology