Jimena Martín Tempestti

Percutaneous coronary intervention (PCI) treats myocardial ischemia by stenting stenotic coronary arteries. Wall shear stress (WSS) is an established indicator of plaque rupture risk and restenosis likelihood, yet is not currently used to guide stenting. To address this gap, we developed a forward-viewing intravascular ultrasound array and demonstrated 3D hemodynamic imaging in coronary artery phantoms. A 3 mm, 172 element forward-viewing 2D array was designed, simulated, and fabricated. Field II was used to simulate aperture performance, and finite element modeling was conducted to investigate element geometry effects on vibrational modes. The array was characterized electrically and acoustically, then used to acquire 3D color flow images in coronary artery-mimicking phantoms using plane wave compounding, SVD-based wall filtering, transverse oscillation velocity estimation, and Fourier sine series WSS estimation. The fabricated array achieved a center frequency of 31 MHz, a -6 dB bandwidth of 60%, and a single-element SNR of 20 ± 1 dB, with 164 of 172 elements operational. Lateral and axial resolutions of 170 μm and 150 μm, respectively, were measured at a depth of 5 mm. Peak velocities of 1 cm/s and 2.6 cm/s were measured in straight and stenotic phantoms, and WSS was derived from these 3D images. 3D finite element modeling provided new insights into element geometry effects on vibrational modes for IVUS 2D arrays, enabling a 31 MHz center frequency, 60% bandwidth, and 95% yield. This work represents the first demonstration of 3D imaging of WSS using a forward-viewing IVUS 2D array, a step toward IVUS-based hemodynamic guidance.

Purpose The Wall Shear Stress (WSS) is the component tangential to the boundary of the normal stress tensor in an incompressible fluid, and it has been recognized as a quantity of primary importance in predicting possible adverse events in cardiovascular diseases, in general, and in coronary diseases, in particular. The quantification of the WSS in patient-specific settings can be achieved by performing a Computational Fluid Dynamics (CFD) analysis based on patient geometry, or it can be retrieved by a numerical approximation based on blood flow velocity data, e.g., ultrasound (US) Doppler measurements. This paper presents a novel method for WSS quantification from 2D vector Doppler measurements. Methods Images were obtained through unfocused plane waves and transverse oscillation to acquire both in-plane velocity components. These velocity components were processed using pseudo-spectral differentiation techniques based on Fourier approximations of the derivatives to compute the WSS. Results Our Pseudo-Spectral Method (PSM) is tested in two vessel phantoms, straight and stenotic, where a steady flow of 15 mL/min is applied. The method is successfully validated against CFD simulations and compared against current techniques based on the assumption of a parabolic velocity profile. The PSM accurately detected Wall Shear Stress (WSS) variations in geometries differing from straight cylinders, and is less sensitive to measurement noise. In particular, when using synthetic data (noise free, e.g., generated by CFD) on cylindrical geometries, the Poiseuille-based methods and PSM have comparable accuracy; on the contrary, when using the data retrieved from US measures, the average error of the WSS obtained with the PSM turned out to be 3 to 9 times smaller than that obtained by state-of-the-art methods. Conclusion The pseudo-spectral approach allows controlling the approximation errors in the presence of noisy data. This gives a more accurate alternative to the present standard and a less computationally expensive choice compared to CFD, which also requires high-quality data to reconstruct the vessel geometry.