Intensity Vector Field: A Tool for Visualization and Characterisation of Tissue Reflections in High Frame Rate Ultrasound Imaging

Abstract

In ultrasound (US) imaging, the reflections from the tissue interfaces are either diffuse or specular based on their sizes relative to the US signal wavelength and acoustic impedance mismatches at the interfaces. Diffuse reflections have low intensity and directivity, unlike specular reflections which have high intensity and directivity that depend on the incidence angle of the transmit signal and the interface orientation. This reduces the detection probability if the apodization in beamforming (as in conventional delay and sum) is inappropriate or the reflections are directed to the outside of the transducer aperture resulting in misdiagnosis (e.g., anisotropy). This puts forth the necessity to consider both the magnitude and direction of the reflected intensity before arriving at a definitive decision. In this work, a novel approach is proposed to represent the spatial distribution of acoustic intensity of each pixel as a vector field. The reflected intensity from each pixel to each transducer element is considered as a vector that has a magnitude and direction and varies depending on the nature of the pixel (diffuse/specular). This approach can supplement visualization, aid in transducer probe adjustment, selection of the right set of transmit angles/focus, and characterization of reflections in musculoskeletal studies and needle tracking.