Understanding Propagation Speed

 

Propagation speed is the speed at which a sound wave travels through a medium.   In our case the medium is tissue.  Sound cannot travel in in vacuum therefore, in order for sound to propagate we must have a medium.  It is the medium or properties of the medium that determine the speed of sound travel.  For soft tissue these properties are density and stiffness. 

Propagation speed in soft tissue is determined by the medium!

DENSITY : How much mass per unit volume.  Increasing density = decrease propagation speed.
STIFFNESS:
The resistance to compressibility.  Increasing stiffness=increase propagation speed.   A decrease in density, compressibility or  elasticity = increase in stiffness (speed) 
Bulk Modulus    

Units In soft tissue 1540 m/s or 1.54 km/s - mm/us

Propagation speed  is determined by the medium (density/stiffness) only!
Cannot
be changed by the sonographer!

Propagation speed (m/s) = Frequency (Hz)  X  Wavelength (meters)

C = F X/-   or  V=F-/

Speeds: bone>tissue>fat>lung  All in m/s:

Bone Muscle Liver Kidney Brain Fat Lung Air
3000 1630 1570 1560 1520 1450 500 330

Propagation speed in soft tissue is determined by the various properties of the medium!

DENSITY: Increasing density = decrease propagation speed.
STIFFNESS:
Increasing stiffness=increase propagation speed.

A decrease in density, compressibility or  elasticity = increase in stiffness (speed) Bulk Modulus    

Don't forget:  Speed = Distance / Time 

                         

**Also don't forget:  Speed = Distance / Time** 

Don't forget to use complimentary units!
(Hz, sec, meter)
     (kHz, msec, cm)     (MHz, mm/usec, mm)