Fig. 1.

Drawing and photos of a 20-MHz Doppler probe designed to measure blood flow velocity noninvasively in mice. The probe consists of a ∼1-mm square piezoelectric crystal, air-backed using Styrofoam, and mounted into a 2-mm-diameter stainless-steel tube with epoxy. A concave epoxy lens is molded to the front face to focus the sound beam at a depth of ∼4 mm. A 10-MHz probe uses a 3-mm tube and is focused at ∼6 mm.