Demonstration of second-harmonic IVUS feasibility with focused broadband miniature transducers

Abstract

Focused broadband miniature polyvinylidene fluoride-trifluoroethylene (PVDF TrFE) ultrasonic transducers were investigated for intravascular (IVUS) second-harmonic imaging. Modeling and experimental studies demonstrated that focused transducers, unlike conventional flat transducers, build up second harmonic peak pressures faster and stronger, leading to an increased SNR of second harmonic content within the coronary geometry. Experimental results demonstrated that focused second harmonic pressures could be controlled to occur at specific depths by controlling the f-number of the transducer. The experimental results were in good agreement with the modeled results. Experiments were conducted using three imaging modalities: fundamental 20 MHz (F20), second harmonic 40 MHz (H40), and fundamental 40 MHz (F40). The lateral resolutions for a 1-mm transducer (f-number 3.2) at F20, F40, and H40 were experimentally measured to be 162, 123, and 124 microm, respectively, which agreed well with the theoretical calculations with <<8% error. Lateral resolution was further characterized in the three modes, using a micromachined phantom consisting of fixed bars and spaces with widths ranging from 20 to 160 microm. H40 exhibited better lateral resolution, clearly displaying 40- and 60-microm bars with about 4 dB and 7 dB greater signal strength compared with F20. Ex vivo human aorta images were obtained in the second-harmonic imaging mode to show the feasibility of high resolution second-harmonic IVUS using focused transducers.

Devolopment of focused IVUS transducer using PMN-PT single crystal

“…For the focused transducer, the value of FWHM is 38 ns, thus the axial resolution was calculated to be 28 flm which is better than the flat transducer (axial resolution = 53flm). After which approximately agreed with the theoretical value determined by the following formula [5]:…”

“…Lateral resolution = wavelength x f-number (5) The actual measured f-number was around 10 which was larger than the design value of 6. Compared with the flat transducer (lateral resolution = 510 flm), the lateral resolution of focused transducer was improved in some degree.…”

“…Unfortunately, as the key component of IVUS system, current commercial IVUS transducers are unfocused with narrow bandwidths and cannot provide good axial (60 /-tm) and lateral resolutions (300 um) due to the lack of focusing ability [4], [5]. The low axial resolution can be attributed to narrow bandwidth of To measure the insertion loss (IL), the transducer was …”

High Performance Relaxor-Based Ferroelectric Single Crystals for Ultrasonic Transducer Applications

“…Among the focusing transducer fabrication methods, the shaped element used in transducers was reported to be much effective for fabricating high-sensitivity devices [68,69]. Hard pressing and pressure defection techniques are the usual ways to shape transducer elements [70–72]. For flexible composite and polymer materials, focusing transducers can be easily fabricated using those techniques.…”

Mapping Intravascular Ultrasound Controversies in Interventional Cardiology Practice

“…Significant academic innovations such as IVUS flow [11], [12], IVUS palpography [8], [13], harmonic IVUS [14], [15] and contrast-enhanced IVUS [9], [16] were to date not taken up by industry. Furthermore, IVUS remains a niche technology, whose clinical practice did not vastly expand nor disappear.…”