Ultrasound Beam Focusing Considering the Cutaneous Fat Layer Effects

Abstract

Commercial medical ultrasound scanners assume average sound velocity of 1540 m/s while sound speed varies at different tissues. This assumption limits focusing quality and degrades contrast and resolution, particularly for patients with fatty abdominal wall. This paper presents a simple two layer model to demonstrate the effect of ultrasound beam focusing quality in inhomogeneous medium based on Huygens's principle. A time delay function for ultrasonic phase array has been derived using in vivo information of fat layer and considering refraction in the interface of two layers. Simulated beam pattern and corresponding beam profiles at the focal depth using conventional delay time and that for proposed two layer model are compared. An experimental setup was designed to assess the image quality using a commercial ultrasound scanner and a phantom of two layers with different sound velocity. Simulated and experimental results indicate that obtained images using time delays for two layer model show better contrast resolution.

Keywords

• Ultrasound beam focusing
• Fat layer effects
• Sound speeds
• Beamforming
• Ultrasound imaging