2D spiral array with defocusing lenses for 3D optoacoustics

Three-dimensional optoacoustic imaging requires either the use of 2D arrays, scanning of single element transducers or 1D arrays. While the latter is time consuming and prone to motion artefacts, fully populated arrays need driving electronics with extremely high channel counts. Sparse arrays are a promising alternative and have shown that similar resolution can be achieved with a considerably reduced element count. However, reducing the element size means a larger active aperture with consequences on the sensitivity. To improve the sensitivity while maintaining a larger element opening angle, which is beneficial for beamforming, we developed a 2D spiral array equipped with element-matched micro-lenses. By applying 256 micro-lenses on top of 4 MHz piezocomposite elements with a diameter of 1.6 mm, we were able to double the opening angle from 15 to 30°. The micro-lense enhanced array was characterized in a phantom study yielding a resolution in the range of 700 μm with delay and sum beamforming. A vessel-like phantom could be reconstructed from a single data set highlighting the potential for 3D optoacoustic imaging.