Diverging polymer lenses for 3D USCT

The latest generation of 3D Ultrasound Computed Tomography (USCT) systems developed at KIT for breast cancer screening employs 128 transducer arrays arranged over a hemispherical aperture. Each array features a piezocomposite disk housing 18 pseudo-randomly distributed single-PZT-fiber elements. The current design achieves isotropic ultrasound emission, a 134% fractional bandwidth, and a 43° opening angle at -10 dB. In this study, we investigated the effect of a diverging polymer lens mounted on the transducer to further increase its opening angle and sensitivity. The acoustic field of a transducer equipped with an in-house fabricated polymethyl methacrylate (PMMA) lens was characterized in an ultrasound testing setup, showing excellent agreement with finite element (FE) simulations. Additional FE simulations were conducted for various lens materials and lens-matching layer combinations, predicting substantial improvements in both the beam width and sensitivity.