The needle tip echo.

The echo of the needle tip used in sonographically guided needle aspiration biopsies was studied in A mode. The biopsy transducer was placed in a water tank and needles parallel to the beam axis were used. The beveled needle tip produced two echoes, which where probably generated by diffraction at the edge of the far end of the tip and by the sharp edge of the needle tip opening. The distal echo was more intense than the proximal one. When a stylet was inserted the proximal echo disappeared as the diffracting edges decreased to a single echo