Design and acoustic characterization of a multi-frequency harmonic array for nonlinear contrast imaging

Two novel ultrasound multi-frequency harmonic transducer arrays (MFHA´s) for contrast enhanced second harmonic (HI) and subharmonic (SHI) imaging have been designed. Each consisted of 3 multi-element piezo-composite sub-arrays (A, B & C) mounted in an arch with a common mechanical focus of 5 cm. The sub-arrays were constructed so the center frequencies were 4f_A=2f_B=f_C (2.5/5.0/10.0 MHz and 1.75/3.5/7.0 MHz). This enabled SHI by transmitting on sub-array C receiving on B and, similarly, from B to A as well as HI by transmitting on A receiving on B and, likewise, from B to C. Transmit and receive pressure levels of the arrays were measured. Following contrast administration, in vitro HI and SHI S/N ratios of up to 40 dB were obtained. In conclusion, the special design of the MFHA produced S/N ratios for HI and SHI comparable to that of regular B-mode and better than commercially available HI systems