Needle visibility for deep punctures with curved arrays

Sonography is the standard technique for monitoring local punctures with needles. Using convex arrays for deeper puncture targets, an increasingly poorer needle visibility is expected. However, it is observed that the needle reappears for large incidence angles of the ultrasound wave to the needle. It is investigated, whether this effect is caused by resonant scattering of the needle. Measurements and simulations demonstrate that resonant scattering occurs for angles of incidence larger than the Rayleigh-angle caused by the excitation of helical guided waves propagating circumferentially and axially. This effect could be exploited to improve needle visibility by adaptive beamforming.