The principle of ultrasound: Difference between revisions

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Ultrasound has been used in medicine since the beginning of the 20th century.

Ultrasound waves are sound waves with a higher than audible frequency. The audible frequency range is 20 hertz (Hz) to 20,000Hz (20kHz). Cardiac imaging applications use an ultrasound frequency range of 1–20MHz (MegaHertz) (1.000.000 – 20.000.000 Hz).

   

To understand ultrasound it is important to understand sound (waves).

Sound is a sequence of waves of pressure that propagate through compressible media such as air or water.

Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart. These regions are known as compressions and rarefactions, respectively. The compressions are regions of high air pressure while the rarefactions are regions of low air pressure.

Since a sound wave consists of a repeating pattern of high-pressure and low-pressure regions moving through a medium, it is sometimes referred to as a pressure wave.

   

   

Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. We won’t go into transverse waves in this chapter about cardiac ultrasound.

Sound waves are characterized by different generic properties:

Frequency (f) = is the number of wavelengths that pass per unit time. It is measured as cycles (or wavelengths) per second and the unit is hertz (Hz).