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The principle of ultrasound: Difference between revisions
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'''Power''' of ultrasound is defined as the rate of energy transfer and is measured in Watts. It is determined by the sound source and it decreases as the beam propagated through the body. | '''Power''' of ultrasound is defined as the rate of energy transfer and is measured in Watts. It is determined by the sound source and it decreases as the beam propagated through the body. | ||
Intensity of the ultrasound beam is defined as the concentration of energy in the beam. Intensity = Power / beam area = (amplitude)^2 / beam area, thus it is measured in Watts per cm^2. It is the key variable in ultrasound safety. Intensity also decreases as the ultrasound propagates through tissue. | Intensity of the ultrasound beam is defined as the concentration of energy in the beam. Intensity = Power / beam area = (amplitude)^2 / beam area, thus it is measured in Watts per cm^2. It is the key variable in ultrasound safety. Intensity also decreases as the ultrasound propagates through tissue. | ||
[[File:PhysicsUltrasound_Fig5.svg|left|500px| Fig. 5]] | |||
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'''Wavelength''' is defined as the length of a single cycle. It is measured in the units of length. It is determined by both the source and the medium. Wavelength cannot be changed by the sonographer. It influences the longitudinal image resolution and thus effect image quality. Typical values of wavelength are 0.1 – 0.8 mm. Wavelength (mm) = Propagation speed in tissue (mm/microsecond) / frequency (MHz). High frequency means short wavelength and vice versa. | '''Wavelength''' is defined as the length of a single cycle. It is measured in the units of length. It is determined by both the source and the medium. Wavelength cannot be changed by the sonographer. It influences the longitudinal image resolution and thus effect image quality. Typical values of wavelength are 0.1 – 0.8 mm. Wavelength (mm) = Propagation speed in tissue (mm/microsecond) / frequency (MHz). High frequency means short wavelength and vice versa. | ||