fig1
Figure 1. Needle visibility depends on the insertion technique used and needle insertion angle. (A) For in-plane insertion (top), both the shaft and tip are visible; however, for out-of-plane insertion, (bottom), only the tip is visible (bottom)[15]; (B) For shallow insertion angles, (first column), specular reflection is high and the needle is visible; however, for steeper insertion angles, (second and third column), needle visibility is lost.
