BASIC PHYSIC OF ULTRASOUND
Basic Physics Of Ultrasound Definition Ultrasound is the term used to describe sound of frequencies above 20 000 Hertz (Hz), beyond the range of human hearing. Frequencies of 1–30 megahertz (MHz) are typical for diagnostic ultrasound. Diagnostic ultrasound imaging depends on the computerized analysis of reflected ultrasound waves, which non-invasively build up fine images of internal body structures. The resolution attainable is higher with shorter wavelengths, with the wavelength being inversely proportional to the frequency. However, the use of high frequencies is limited by their greater attenuation (loss of signal strength) in tissue and thus shorter depth of penetration. For this reason, different ranges of frequency are used for examination of different parts of the body: ■ 3–5 MHz for abdominal areas ■ 5–10 MHz for small and superficial parts and ■ 10–30 MHz for the skin or the eyes. Generation of ultrasound Piezoelectric crystals or materials are