A multifocal acoustic lens-transducer system for reverberant optical coherence elastography

Reverberant optical coherence elastography (RevOCE) relies on multiple external excitation sources, such as mechanical actuators or vibrators, to produce random waves propagating in arbitrary directions. In this work, a preliminary study on acoustic beam manipulation to produce multi-focal acoustic radiation force is introduced using a planar ultrasound transducer and a 3D-printed acoustic lens array for RevOCE. An unfocused acoustic beam generated by an ultrasound transducer with 1 MHz central frequency and 38-mm element diameter was coupled to seven uniformly distributed acoustic focusing lenses. The spatial distribution of the acoustic field at the focal plane was measured with a needle hydrophone. The effectiveness of the system in generating reverberant shear wave fields was assessed by performing RevOCE imaging of tissue-mimicking gelatin phantoms. The multi-focus acoustic lens-transducer system was coupled with a phase-sensitive optical coherence tomography (PhS-OCT) system. The RevOCE measurement was conducted by sending ten cycles of a tone burst at 2 kHz. The measured acoustic pressure field showed that the array of concave spherical acoustic lenses spatially distributed the acoustic energy into multiple focal spots in the desired focal plane. Furthermore, RevOCE imaging in tissue-mimicking phantom indicated the effectiveness of the acoustic lens-transducer system in inducing reverberant shear wave fields for probing mechanical properties.