Using K-Wave to Simulate Ultrasound for Optimal Intravascular Ultrasound Device Frequencies

Cardiovascular diseases are the leading cause of death worldwide; they accounted for 17.9 million deaths or an estimated 32% of all deaths in 2019. The rupture of vulnerable atherosclerotic plaques is a major cause of cardiovascular diseases. Atherosclerotic plaques are characterized by the thickening or hardening of blood vessel walls due to the build-up of fats, cholesterol, and other materials, between the intima and adventitia. Angiography is commonly used for the diagnosis of cardiovascular diseases. However, it is more for vessel stenosis detection with a general overview of vessel structure; it is challenging to apply angiography for meticulous examination of plaques. Intravascular ultrasound (IVUS) is a catheter-based diagnostic device using echo-pulsed ultrasound for imaging from within arteries. IVUS can be used as an adjunct of angiography and, in contrast to the latter, it is critical for detailed imaging by detecting the exact location and morphology of plaques. A conventional IVUS device employs a piezoelectric transducer for transmitting and receiving ultrasound waves with a single frequency. Although higher ultrasound frequencies enable greater image resolution, it suffers stronger attenuation within biological tissues, which diminishes the penetration depth of the ultrasound signal and thus limits the view of imaging. This means that a single frequency cannot account for all situations as plaques may have various morphologies and sizes, and employing an IVUS catheter with a suitable frequency is crucial for the accurate identification of atherosclerotic plaques. Therefore, a systematic study of the impacts of ultrasound frequency on IVUS imaging of atherosclerotic plaques is significant. The ideal method would be testing IVUS catheters with different frequencies for various plaques, however, the cost of IVUS catheter and plaque prop fabrication will be staggeringly large as ultrasound frequency has a very wide range. To address this issue, we present a solution in this work: a numerical simulation platform to mimic IVUS imaging of atherosclerotic plaques. The platform is built off the K-Wave toolbox in Matlab which is designed for time-domain acoustic simulations in complex and tissue-realistic media. The ultrasound transmitter and sensor functions were combined to simulate a piezoelectric transducer, which was spatially scanned to mimic imaging implementation in IVUS. The frequency of the IVUS was made adjustable in the simulation, and IVUS imaging of the same plaque was achieved with varying frequencies. The evolution of image quality was quantitively characterized with edge spread function, indicating that high-frequency IVUS can produce images with higher axial resolution but less penetration depth while lower-frequencies have the inverse effect, which is consistent with the physical theory. IVUS images of plaques with various shapes, sizes, and mechanical properties were also demonstrated. As such, this simulation platform offers a tool for the study of IVUS imaging. Further steps on this project will be taken to create a graphical user interface that is more user-friendly for clinicians, so it is promising to be used in clinical scenarios to guide IVUS catheter selection for the identification of atherosclerotic plaques.