Design factors of intravascular dual frequency transducers for super-harmonic contrast imaging and acoustic angiography

Abstract

Imaging of coronary vasa vasorum may lead to assessment of the vulnerable plaque development in diagnosis of atherosclerosis diseases. Dual frequency transducers capable of detection of microbubble super-harmonics have shown promise as a new contrast-enhanced intravascular ultrasound (CE-IVUS) platform with the capability of vasa vasorum imaging. Contrast-to-tissue ratio (CTR) in CE-IVUS imaging can be closely associated with the low frequency transmitter performance. In this paper, transducer designs encompassing different transducer layouts, transmitting frequencies, and transducer materials are compared for optimization of imaging performance. In the layout selection, the stacked configuration showed superior super-harmonic imaging compared with the interleaved configuration. In the transmitter frequency selection, a decrease in frequency from 6.5 MHz to 5 MHz resulted in an increase of CTR from 15 dB to 22 dB when receiving frequency was kept constant at 30 MHz. In the material selection, the dual frequency transducer with the lead magnesium niobate-lead titanate (PMN-PT) 1-3 composite transmitter yielded higher axial resolution compared to single crystal transmitters (70 μm compared to 150 μm pulse length). These comparisons provide guidelines for design of intravascular acoustic angiography transducers.

Dual-frequency IVUS array for contrast enhanced intravascular ultrasound imaging

“…The thickness of the PI substrate is 12.5 μm and a 2 μm copper circuit was patterned on it. This isolation layer does not significantly affect the low frequency transmission because the isolation layer is thin compared to the wavelength of the low frequency mode in PI (1244 μm) [16][17][18]. Similarly, it was expected that the 2 μm thick copper electrode would not impact the isolation function since it is negligibly thin compared to the wavelength of the receiving array in copper (170 μm).…”

Intravascular Ultrasound Imaging With Virtual Source Synthetic Aperture Focusing and Coherence Factor Weighting

“…Integrated IVUS and optical coherence tomography (OCT) imaging [4–6], and multi-frequency IVUS imaging [7] [8] were proposed to identify thin fibrous cap utilizing high resolution information from OCT or high frequency IVUS. Integrated IVUS and near-infrared spectroscopy (NIRS) imaging [9, 10], integrated IVUS and intravascular photoacoustic (IVPA) imaging [11, 12], and integrated IVUS, OCT and Fluorescence imaging [13, 14] are developed to characterize the chemical composition of the plaque.…”

Combining Subharmonic and Ultraharmonic Modes for Intravascular Ultrasound Imaging: A Preliminary Evaluation

“…Several nonlinear CE-IVUS techniques have been reported using in vitro (Goertz et al, 2006a; Ma et al, 2015) and in vivo flow models (Goertz et al, 2006b, 2007). Nonlinear CE-IVUS imaging is typically performed with the aid of multi-pulse techniques such as pulse inversion imaging (Frijlink et al, 2011).…”

“…Subharmonic and ultraharmonic imaging modes are robust to artifacts produced from nonlinear propagation, leading to substantial improvements in CTR relative to fundamental-mode imaging (Goertz et al, 2007; Maresca et al, 2013; Daeichin et al, 2015). Acoustic angiography IVUS is another promising technique that employs excitation at conventional diagnostic frequencies and displays the signal from UCA at high frequencies (> 20 MHz) to reduce the impact of nonlinear propagation (Ma et al, 2015; Martin et al, 2016). The excellent resolution of acoustic angiography is encouraging for visualizing the microcirculation.…”