Miniaturized dual-element transducer-based intravascular ultrasonic elastography: a preliminary in vivo study

Acute coronary syndrome (ACS) is triggered by the rupture or erosion of unstable atherosclerotic plaques in coronary arteries, which induces thrombosis and ultimately results in myocardial hypoperfusion. In current clinical practice, treatment strategies for ACS are predominantly guided by the assessment of vascular stenosis severity, while the key indicator of plaque vulnerability (i.e., plaque nature) is largely overlooked. This oversight may lead to suboptimal therapeutic decisions and adversely affect patient outcomes. This study thus aimed to develop an ultrasound technology-based system capable of imaging intravascular structures and analyzing plaque characteristics.

In this study, two ultrasound transducers with different frequencies were integrated into a single microcatheter: a low-frequency-focused transducer for generating a sufficient acoustic radiation force to induce shear waves in tissue and a high-frequency imaging transducer for acquiring high-resolution structural images. Structural imaging data were analyzed to determine the shear wave propagation speed, enabling calculation of tissue stiffness and simultaneous imaging of both the morphological and mechanical properties for comprehensive tissue characterization. The safety of the dual-frequency system was confirmed through precise acoustic output measurements and calculations, and compliance with established safety standards was established. To evaluate the feasibility of simultaneously assessing coronary artery morphology and functional properties in the context of coronary artery disease, three sets of experiments were performed: elastomeric phantom tests with varying stiffness, ex vivo porcine coronary artery experiments, and in vivo rabbit abdominal aortic plaque studies.

The acoustic performance of the dual-frequency ultrasound transducers was characterized via echo measurements and spectral analysis, yielding center frequencies of 9.78 and 36.35 MHz and corresponding peak-to-peak echo amplitudes of 1,682 and 380.4 mV, respectively. Based on peak displacement and shear-wave velocity measurements in phantom imaging, the lateral and axial resolutions of the low-frequency driving transducer were determined to be 440.3 and 320.3 µm, respectively, whereas those of the high-frequency imaging transducer were 369.2 and 312.2 µm, respectively. Through the comparison of the mechanical properties of porcine coronary arteries before and 20 minutes after formalin fixation, the Young modulus of the vessels in the native state was determined to be 69.6±6.3 kPa, which increased to 140.3±16.3 kPa after fixation. These results further confirmed the system's ability to detect tissues of varying stiffness levels. In vivo measurements revealed a significant stiffness contrast between atherosclerotic plaques (4.9±0.3 kPa) and normal vessel walls (39.6±2.5 kPa). These results demonstrate that the dual-frequency system can quantitatively differentiate mechanical properties of vascular tissues with high sensitivity.

This study developed a focused dual-element intravascular ultrasound transducer with an outer diameter of 1.55 mm. Its performance was rigorously evaluated through phantom measurements, ex vivo porcine artery experiments, and in vivo rabbit studies, which collectively demonstrated the feasibility of this device for real-time intravascular elastography.