Recent studies have shown the feasibility of tissue and contrast harmonic imaging with a prototype nonlinear intravascular ultrasound (IVUS) system using a conventional single-element rotating IVUS catheter. In this study, a dual-frequency transducer element was mounted in an IVUS catheter and its second harmonic imaging performance was investigated and compared with that of a conventional IVUS catheter. Hydrophone measurements showed a transmit efficiency improvement of > 6 dB for the dual-frequency catheter at 20 MHz. In vitro phantom experiments showed a signal-to noise ratio improvement of > 5 dB in second harmonic mode at 40 MHz (H40) with the dual-frequency catheter, when using equal transmit voltage for both catheters. Finally, in vivo experiments were conducted and showed image improvement in H40 acquisitions with respect to the conventional IVUS catheter.

A recent study has shown the feasibility of tissue harmonic imaging (THI) using an intravascular ultrasound (IVUS) transducer. This correspondence describes the design, fabrication, and characterization of a THI-optimized piezoelectric transducer with oval aperture of 0.75 mm by 1 mm. The transducer operated at 20 MHz and 40 MHz, and was comprised of a single piezoelectric layer with additional passive layers. The Krimholtz-Leedom-Matthaei (KLM) model was used to iteratively find optimal material properties of the different layers. The transducer characterization showed -6 dB fractional bandwidths of 30% and 25%, and two-way insertion losses of -20 dB and -36 dB, respectively.

Recent studies have suggested the feasibility of tissue harmonic imaging (THI) with intravascular ultrasound (IVUS). This paper describes the design, fabrication and characterization of a piezoelectric transducer optimized for tissue harmonic IVUS. Ideally, such a transducer should efficiently transmit a short acoustic pulse at the fundamental transmission frequency and should be sensitive to its second harmonic echo, for which we have chosen 20 MHz and 40 MHz, respectively. The intravascular application limits the transducer dimensions to 0.75 mm by 1 mm. The transducer comprises of a single piezoelectric layer design with additional passive layers for tuning and efficiency improvement, and the Krimholtz-Leedom-Matthaei (KLM) model was used to find iteratively optimal material properties of the different layers. Based on the optimized design a prototype of the transducer was built. The transducer was characterized by water-tank hydrophone measurements and pulse-echo measurements. These measurements showed the transducer to have two frequency bands around 20 MHz and 40 MHz with -6dB fractional bandwidths of 30% and 25%, and round-trip insertion losses of -19 dB and -34 dB, respectively.