#Ultrasound physics 101 series
Continuous expansion and contraction of the crystal surface by an external power source introduces energy into the medium as a series of compressions and rarefactions, traveling as a wave front in the direction of travel, known as a longitudinal wave, as shown in Fig. The mechanical energy imparted at the surface is transferred to adjacent particles of the medium, which travels at the speed of sound through the medium. Contraction of the crystal follows, causing a decrease in pressure. During transducer surface expansion, an increase in the local pressure at contact occurs. Compression is caused by a mechanical inward deformation by an external force, such as an expanding and contracting transducer crystal composed of multiple elements in contact with the medium.
Sound is mechanical energy that propagates through a continuous, elastic medium by the compression (high pressure) and rarefaction (low pressure) of particles that comprise it. This chapter describes the characteristics, properties, and production of ultrasound interaction with tissues, acquisition, processing, and display of the ultrasound image the instrumentation achievable measurements, including blood velocity and safety issues. An understanding of the basic physics of ultrasound, in addition to hands-on training, practice, and development of experience are of great importance in its effective and safe use. The success of ultrasound for this purpose is attributed to several characteristics, including the low cost and portability of ultrasound devices, the nonionizing nature of ultrasound waves, and the ability to produce real-time images of the acoustic properties of the tissues and tissue structures in the body to deliver timely patient care, among many positive attributes. Imaging systems using ultrasound have attained a large presence as point-of-care (PoC) devices across many clinical domains over the past 10 years.
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