Bahram Jadidian

25 MHz ultrasonic transducers with lead- free piezoceramic, 1-3 PZT fiber-epoxy composite, and PVDF polymer active elements

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K0.44Na0.52Li0.04)(Nb0.84Ta0.10S0.06b)O3 powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and kt of 0.50, the KNN-LT-LS composition may be a good candidate for high frequency transducer applications. PZT fibers with 25 mum diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged kt = 0.64 and d33 = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 Omega and higher thickness coupling coefficient of the ceramic transducer.

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

Two novel ultrasound multi-frequency harmonic transducer arrays (MFHAs) 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/sub A/=2f/sub B/=f/sub 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.

Synthetic Structural Imaging (SSI): A new ultrasound method for tracking breast cancer morphology

A new signal interrogation concept, based on Synthetic Structural Imaging (SSI) physics, has been developed to guide therapies. The SSI method was previously successful in radar and sonar imaging; here it is demonstrated for acoustic scattering from penetrable biological targets. Operating at ultrasonic frequencies of several hundred kilohertz, SSI trades the higher resolution of typical B-mode ultrasound imaging for a significantly stronger correlation to target shape and volume, which are among the primary tissue classifiers. Tissue phantom models were fabricated with embedded spheroidal inclusions ranging from 2.41 mm through 6.3 mm in diameter. The phantom medium was 10 wt% porcine gelatin and the inclusions were 28 wt% porcine gelatin. The inclusion dimensions were measured with calipers. The phantom was interrogated with two impulse-excited Panametrics transducers: a model V301 with a peak frequency of 0.50 MHz and a −6 dB bandwidth of 81%, and a model V314 with a peak frequency of 0.99 MHz and a −6 dB bandwidth of 77%. The backscattered RF data were digitized, recorded, and digitally bandpass-filtered. The experimental profile functions were computed. Volumes were estimated by integrating the experimental profile functions. SSI-determined volume ratios were demonstrated to be within 7% to 18% of caliper-determined volume ratios.