Development Of Ultrasound Transducers Research Articles

Ultrasound‐gated computed tomography coronary angiography: Development of ultrasound transducers with improved computed tomography compatibility

Cardiovascular disease (CVD) is a leading cause of death worldwide, with coronary artery disease (CAD) accounting for nearly half of all CVD deaths. The current gold standard for CAD diagnosis is catheter coronary angiography (CCA), an invasive, expensive procedure. Computed tomography coronary angiography (CTCA) represents an attractive non-invasive alternative to CCA, however, CTCA requires gated acquisition of CT data during periods of minimal cardiac motion (quiescent periods) to avoid non-diagnostic scans. Current gating methods either expose patients to high levels of radiation (retrospective gating) or lead to high rates of non-diagnostic scans (prospective gating) due to the challenge of predicting cardiac quiescence based on ECG alone. Alternatively, ultrasound (US) imaging has been demonstrated as an effective indicator of cardiac quiescence, however, ultrasound transducers produce prominent streak artifacts that disrupt CTCA scans. In this study, a proof-of-concept array transducer with improved CT-compatibility was developed for utilization in an integrated US-CTCA system. Alternative materials were tested radiographically and acoustically to replace the radiopaque acoustic backings utilized in low frequency (1-4MHz) cardiac US transducers. The results of this testing were used to develop alternative acoustic backings consisting of varying concentrations of aluminum oxide in an epoxy matrix via simulations. On the basis of these simulations, single element test transducers designed to operate at 2.5MHz were fabricated, and the performance of these devices was characterized via acoustic and radiographic testing with micro-computed tomography (micro-CT). Finally, a first proof-of-concept cardiac phased array transducer was developed and its US imaging performance was evaluated. Micro-CT images of the developed US array with improved CT-compatibility were compared with those of a conventional array. Materials testing with micro-CT identified an acoustic backing with a measured radiopacity of 1008 HU, more than an order of magnitude lower than that of the acoustic backing (24,000 HU) typically used in cardiac transducers operating in the 1-4MHz range. When utilized in a simulated transducer design, this acoustic backing yielded a -6-dB fractional bandwidth of 57%, similar to the 54% bandwidth of the transducer with the radiopaque acoustic backing. The developed 2.5MHz, single element transducer based on these simulations exhibited a fractional bandwidth of 51% and signal-to-noise ratio (SNR) of 14.7dB. Finally, the array transducer developed with the acoustic backing having decreased radiopacity exhibited a 56% fractional bandwidth and 10.4dB single channel SNR, with penetration depth >10cm in phantom and in vivo imaging using the full array. The first attempt at developing a CT-compatible ultrasound transducer is described. The developed CT-compatible transducer exhibits improved radiographic compatibility relative to conventional cardiac array transducers with similar SNR, bandwidth, and penetration depth for US imaging, according to phantom and in vivo cardiac imaging. A CT-compatible US transducer might be used to identify cardiac quiescence and prospectively gate CTCA acquisition, reducing challenges associated with current gating approaches, specifically relatively high rates of non-diagnostic scans for prospective ECG gating and high radiation dose for retrospective gating.

A tunable gradient impedance matching layer based on piezoelectric materials with external circuits

The impedance step between different materials inevitably leads to serious energy loss during acoustic emission, transmission, and receiving. In this paper, a tunable gradient impedance matching layer (TGIML) was designed and fabricated to eliminate the impedance step. The TGIML was composed of periodical piezoelectric disks with shunting capacitors. Through the elaborate modulation of the capacitances of the shunting capacitors, the proposed TGIML can adapt interfaces formed by different materials. Two interfaces formed by solid rods were constructed to demonstrate the performance of the TGIML. The simulated and experimental results verified that, after inserting the TGIML, the transmission could be enhanced significantly in a wide frequency range for both interfaces. We believe that the proposed TGIML has great potential for wide applications in the development of ultrasound transducers, nondestructive testing, and energy harvesting.

Development of Ultrasound Transducer with Double-Peak-Type Frequency Characteristics for Harmonic Imaging and Subharmonic Imaging

Development of ultrasound transducers with double-peak-type frequency characteristics for harmonic imaging and subharmonic imaging is reported in this paper. The peak on the low-frequency side in the frequency characteristics is used to transmit ultrasound into tissues or microbubble ultrasound contrast agents, and another peak on the high-frequency side is used to receive the second harmonic component in the ultrasound transducer with double-peak-type frequency characteristics for harmonic imaging. On the other hand, the peak on the high-frequency side in the frequency characteristics is used to transmit ultrasound and another peak on the low-frequency side is used to receive the 1/2 subharmonic component in the ultrasound transducer with double-peak-type frequency characteristics for subharmonic imaging. The results of the transducer design based on numerical calculation are reported in this paper.