ABSTRACT
This chapter describes the elements of US medical imaging, an example of an imaging system, energy transduction, beam control, signal processing, and display methods. Images are formed by sending a short pulse of high frequency sound into the body and detecting weak reflections from scatterers within soft tissues. The method is similar to radar or sonar but on a different scale. Speed in the soft tissues of the body is assumed to be approximately 1540 m/sec in modern imaging instruments. This assumption is violated in many cases; for instance, the speed of sound in fat can be as low as 1430 m/sec. Lateral localization of the focusing ultrasonic beam is accomplished by electronically controlling the phase and amplitude of the motion of the transducer surface in transmit mode and by dynamic focusing in receive mode. An important aspect of medical imaging that is not important in nondestructive evaluation or other acoustic imaging disciplines is the contrast of the image.
