A preliminary engineering design of intravascular dual-frequency transducers for contrast-enhanced acoustic angiography and molecular imaging

Abstract

Current intravascular ultrasound (IVUS) probes are not optimized for contrast detection because of their design for high-frequency fundamental-mode imaging. However, data from transcutaneous contrast imaging suggests the possibility of utilizing contrast ultrasound for molecular imaging or vasa vasorum assessment to further elucidate atherosclerotic plaque deposition. This paper presents the design, fabrication, and characterization of a small-aperture (0.6 × 3 mm) IVUS probe optimized for high-frequency contrast imaging. The design utilizes a dual-frequency (6.5 MHz/30 MHz) transducer arrangement for exciting microbubbles at low frequencies (near their resonance) and detecting their broadband harmonics at high frequencies, minimizing detected tissue backscatter. The prototype probe is able to generate nonlinear microbubble response with more than 1.2 MPa of rarefractional pressure (mechanical index: 0.48) at 6.5 MHz, and is also able to detect microbubble response with a broadband receiving element (center frequency: 30 MHz, −6-dB fractional bandwidth: 58.6%). Nonlinear super-harmonics from microbubbles flowing through a 200-µm-diameter micro-tube were clearly detected with a signal-to-noise ratio higher than 12 dB. Preliminary phantom imaging at the fundamental frequency (30 MHz) and dual-frequency super-harmonic imaging results suggest the promise of small aperture, dual-frequency IVUS transducers for contrast-enhanced IVUS imaging.

Intravascular Molecular Imaging for Atherosclerosis

“…A new type of dual-frequency IVUS for detecting microbubbles was recently proposed for imaging vaso vasorum within arteries. 1 The contrast agents were originally non-specific perfusion materials, but are currently more targeted with a coating linked to an …”

Development of transmitters in dual-frequency transducers for interventional contrast enhanced imaging and acoustic angiography

“…The 4/30 MHz dual frequency transducer design was introduced with highfrequency 3-D contrast imaging of in vivo microvasculature [1,5], but the transducer size was not practical for interventional applications. Recently, the sandwich design of a small-aperture 6.5/30 MHz transducer made of PMN-PT crystals for the application of the contrast enhanced intravascular ultrasound (CE-IVUS) has been reported [7]. The simple design of this dual-frequency transducer showed promising performance with a small size aperture (0.6 × 3 mm 2 aperture and < 600 μm thickness).…”

An acoustic filter based on layered structure

“…Filters are fundamental devices that underpin the functionality of a broad range of multiple frequency systems including microwave, 1 optical, 2 digital, 3 and mechanical 4,5 systems. Specifically in multi-frequency vibration systems, delicate wave propagation control is needed to make sure of the soundness and efficiency of the system.…”

“…[13][14][15][16] In multi-frequency acoustic systems, the wave sources and propagation are typically spatial-asymmetric. For instance, in dual frequency ultrasound transducers 4,17,18 that showed promising results for super-harmonic microscopy, 19 fundamental, and harmonic frequency ultrasound waves propagate in opposite directions. It is necessary that the low frequency (LF) wave propagates forward efficiently, while the harmonic high frequency (HF) wave does not propagate backward after reaching the high frequency active layer ( Fig.…”

“…This acoustic filter is readily implemented in multi-frequency acoustic systems, such as dual frequency ultrasonic transducers, which could be used in super-harmonic imaging 4 and therapy-imaging 5 applications. This acoustic filter design is guided by the microwave circuit design theory, and does not involve any microstructures or non-linearity, making its fabrication cost-effective.…”