The principle of ultrasound: Difference between revisions

'''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.   

'''Propagation speed''' in human soft tissue is on average 1540 m/s.  It is defines as to how fast the ultrasound can travel through that tissue.  It is determined by the medium only and is related to the density and the stiffness of the tissue in question.  Density of the medium is related to its weight and the stiffness of the medium is related to its “squishability”.  As the medium becomes more dense, the slower is speed of ultrasound in that medium (inverse relationship).  The stiffer the tissue, the faster will the ultrasound travel in that medium (direct relationship).  There are tables where one can look up the velocity of sound in individual tissues.