The principle of ultrasound: Difference between revisions

[[File:PhysicsUltrasound_Fig2.svg|left| Fig. 2]]

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Frequency is the inverse of the period and is defined by a number of events that occur per unit time.  The units of frequency is 1/sec or Hertz (Hz).  Since f = 1/P, it is also determined by the source and cannot be changed.   

'''Amplitude''' is an important parameter and is concerned with the strength of the ultrasound beam.  It is defined as the difference between the peak value and the average value of the waveform.  It is expressed in decibels or dB, which is a logarithmic scale.  It can be changed by a sonographer.  Amplitude decreases as the ultrasound moves through tissue, this is called attenuation.  Amplitude decreases usually by 1 dB per 1 MHz per 1 centimeter traveled.  For example, if we have a 5 MHz probe and the target is located at 12 cm (24 cm total distance), then the amplitude attenuation will be 1 dB x 5 MHz x 24 cm = 120 dB  which nearly 6000 fold decrease.