High frequency transducers for medical ultrasonic imaging

A wide variety of fabrication techniques and materials produce ultrasound transducers with very different performance characteristics. High frequency (50 MHz), focused single element transducers using lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO₃) ceramic, polyvinylidene fluoride (PVDF) polymer and lithium niobate (LiNbO₃) single crystal are compared in design and performance. The transducers were all contacted with a 3 mm aperture and f-number of 2-3. Design considerations discussed include optimization of designs using different lens, backing and matching materials for acoustic matching and the use of several electrical tuning techniques to match the transducers to the 50 Ω circuitry. Transducers were tested for insertion loss and -6 dB bandwidth using a quartz fiat-plate target. Insertion loss measurements between transducers were -20 dB to -50 dB with bandwidths in the range of 50-120%. Through the use of an ultrasound backscatter microscope (UBM), the transducers were compared using in vitro images of the human eye. Images of a wire phantom were also made for comparison of lateral and axial resolution of each device.