Ultrasound Imaging

Abstract

Ultrasound imaging makes use of the properties of sound waves in tissue. Pressure waves in the low megahertz range travel through tissue at the speed of sound, being refracted and partially reflected at interfaces. Ultrasound contrast is therefore related to echogenic inhomogeneities in tissue. The depth of an echogenic object can be determined by the travel time of the echo. By emitting focused sound waves in different directions, two-dimensional scans are possible. Ultrasound images are highly qualitative in nature due to the complex relationship between inhomogeneous tissue and the echoes, due to the differences in speed of sound in different tissues, and due to the high noise component that is a result of the weak signal and high amplification. Ultrasound images show good soft tissue contrast, but fail in the presence of bone and air. Although ultrasound images can be generated with purely analog circuitry, modern ultrasound devices use computerized image processing for image formation, enhancement, and visualization. Ultrasound imaging is very popular because of its low-cost instrumentation and easy application. However, an ultrasound exam requires the presence of an experienced operator to adjust various parameters for optimum contrast, and ultrasound images usually require an experienced radiologist to interpret the image.