ENGINEER 1C03 Lecture Notes - Lecture 17: Osteoporosis, Radiography, Bone Density
9 Nov 2017
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Define the ratio of reflected to initial intensity as: The acoustic impedances of two adjoining tissues are used to calculate the intensity of the reflected pulse compared with the incoming one. I0 = intensity of the pulse, incident on the surface (w m-2) Ir = intensity of the pulse reflected back (w m-2) Z1 and z2 = the acoustic impedances of media 1 and 2 (kg m-2 s-1) The ratio of the reflected ultrasound should almost always be less than its incident ultrasound wave. The ratio will be given as a decimal point which should be converted to a percentage: identify that the greater the difference in acoustic impedance between two materials, the greater is the reflected proportion of the incident pulse. If there is a very large difference in acoustic impedance between the two materials, a large fraction of the ultrasound will be reflected back. This is what happens when ultrasound is directed through the air to the skin.
