Analysis of Aberration Effects on Flow Imaging and Quantification in Echocardiography

Abstract

In medical ultrasound, aberration is a phenomenon that causes distortion of the ultrasound wavefront as it travels through an inhomogeneous medium. Aberration has been investigated since the 1960s and is known as a major cause of image quality loss in several applications, such as abdominal, breast, transcranial, and cardiac imaging. In the attempt to improve image quality in the presence of aberration, research has focused on two fronts: to provide deeper understanding of the physics behind aberration, and to develop robust methods for aberration correction based on such knowledge. However, most of the work found in the literature is focused towards improving BMode image quality, whereas little attention is given to other modalities. The aim of this work is to investigate the effects of aberration on two established blood flow imaging and quantification modalities, Pulsed Wave (PW) Doppler and Color Flow. The study was carried out on phantom and in-vivo recordings, using acquisitions and aberration conditions commonly encountered in cardiac imaging. In this work, aberration was modeled as a near-field phase screen, allowing for easier design and manufacturing compared to more realistic models. The results indicate that, as in BMode imaging, aberration degrades signal-to-noise ratio and resolution. Moreover, the increased sample volume size can significantly affect mean velocity and variance estimates in Color Flow, especially in the presence of strong velocity gradients occurring laterally to the beam direction. Similar effects were observed in PW Doppler. The conclusion is that blood flow imaging and quantification modalities in cardiac applications can potentially benefit from the development of aberration correction methods.