Hybrid dual frequency transducer and Scanhead for micro-ultrasound imaging

We report on the design, assembly and evaluation of a dual frequency mechanically scanned transducer for ultrasound bubble manipulation and real time high frequency imaging applications. A low frequency 2 MHz annulus was designed to fit on the outside of a commercially available 30 MHz, 100% bandwidth single element fixed focus transducer such that the axial axes of each transducer would be substantially aligned. The acoustic pressure and beam characteristics of the low frequency transducer were characterized as a function of transmit center frequency and drive voltage. The focal depths of the low and high frequencies were measured to be 11.8-12.1 mm and 12.7 mm for transmit pulses of 2-3 MHz and 30 MHz respectively. The probe was integrated into a commercially available Visualsonics RMV Scanhead and could achieve a frame rate of 20 fps. The dual frequency probe provided an average of >12 dB enhancement of contrast to tissue ratios in rat kidney and rat xenograft Fibrosarcoma models.