Caused by either reflection or absorption. Gas causes a dirty shadow secondary to reflection. Stones and bones cause clean shadows secondary to absorption.
Sound is attenuated as it passes through tissue, with more attenuation through solids than liquids. As sound passes through a cystic structure (i.e. less attenuation than surrounding tissue) the structure deep to the cyst will appear brighter then the adjacent tissue. This effect is also seen in adjacent solid structures with different attenuation.
Results from a flat surface or sound plane (ex. lung-liver interface) reflecting sound from a solid object back to the transducer creating a duplicate image.
Occurs when sound travels obliquly through a transition plane causing a change in speed and bending of the sound which may result in duplication of a structure.
When sound bounces back quickly then echos off the transducer appearing as bright bands.
Usually caused by gas and resonating fluid around a gas bubble, appearing as a solid bright line with echogenic shadow. This can also be seen with a metallic fragment.
When a structure is picked up by a minor beam adjacent to the main beam it can echo in the path of the main beam. Often lost in adjacent tissue, can be seen when projects over a cyst or fluid filled structure.
Occurs when the Doppler PRF is less than twice the shift. It causes a high frequency flow to wrap around from the positive extreme of the scale to a negtive value, or causing a dark red to appear as a light blue.
Turbulence in a vessel can cause vibration in the wall and result in color shift on Doppler.