Effect of needle rotation (A-I) compared with no rotation (J-R) in a non-surgical subject needled on the thigh bilaterally shown with ultrasound B-scans (A,C,J,L), tissue displacement maps (B,K) and semi-variogram plots (D-I,M-R). Needle position is indicated by oblique line originating from left upper corner of images. Tissue displacement maps show maximal tissue displacement in the area surrounding the needle with rotation (B) compared with no rotation (K). Semi-variograms were computed from all ultrasound data points included in the region of interest (10 mm × 5 mm) indicated by box in the directions parallel (D-F, M-O) and perpendicular (G-I, P-R) to the skin. In Panels D-I, each semi-variogram line represents one ultrasound frame before rotation (D,G), during rotation (E,H) and after 8 full uni-directional rotations (F,I). Panels M-R show semi-variograms for sequential frames with needle insertion alone without rotation (time period equivalent to panels D-I). Frame numbers are shown in inset for each semi-variogram.