Figure 4.

Images of a hypodermic needle inserted perpendicular to the US transducer. The needle is inserted horizontally through the pork loin sample. The transducer is located toward the top of the images. (a) US image of the needle cross section in pork sample; (b) PA image of needle cross section, where the needle is easily visible; (c) US image of the needle and tissue in the transducer imaging plane; and (d) PA image of the needle in the transducer imaging plane, where the metal needle is clearly visible. The dimensions of the pork loin are approximately 30×30×30 mm³. US images are displayed at 40 dB, PA images at 20 dB.