Development of single-fiber piezocomposite transducers for 3D ultrasound computer tomography

Ultrasound Computer Tomography (USCT) medical imaging is a promising approach for early detection of breast cancer. At Karlsruhe Institute of Technology (KIT) a 3D USCT system is developed. The system operates 2041 ultrasound transducers in a semi-ellipsoidal aperture surrounding a region of interest (ROI) of 10 cm x 10 cm x 10 cm. Results from a first patient study reveal the requirement of a significantly increased ROI to cover bodily variations. Design considerations and simulations show a demand for circular transducers of approximately 500 mm diameter, increasing the opening angle of the transducers to approximately 60°. Piezofiber composite technology is predestinated to simply provide circular transducers of the required dimensions. Moreover, piezocomposites based on single PZT (lead zirconate titanate Pb[ZrxTi1-x]O3) fibers enable a cost-effective and series-production alternative to currently used dice-and-fill composites. A transducer design is presented which utilizes individually arranged single piezoceramic fibers with 460 µm in diameter within piezocomposite discs. As result fibers are independently addressable as single transducer elements allowing for the desired transducer arrangement. The electrical performance of each piezoceramic fiber is determined proofing a strong dependence of coupling coefficient and resonance frequency from transducer thickness. In further processing, the piezocomposite discs are connected to printed circuits, integrated into a cylindrical housing and backfilled with polyurethane. Ultrasound characteristics such as sound pressure and opening angle are evaluated quantitatively. The transducer opening angles are in the expected range, desired center frequency is achieved and bandwidth preserved compared to former dice-and-fill transducers.