Acoustic saturation occurs when received signals reach a system's
high-amplitude limit. At that point the system becomes unable to distinguish or
display signal intensities. At the point of saturation, increased input will not
increase output.
Aliasing occurs when the detected Doppler frequency exceeds the Nyquist
limit. It is characterized on the spectral display by the Doppler peaks going off
the display, top or bottom, and then continuing on the other side of the baseline.
On the Color display an immediate change in color from one Nyquist limit to
the other is seen.
Comet tail is a form of reverberation artifact produced when two or more
strong reflectors are close together and have a high propagation speed. In this
case, sound does not travel directly to a reflector and back to the transducer;
and a strong linear echo appears at the reflector and extends deeper than the
reflector.
Enhancement is an increased relative amplitude of echoes caused by an
intervening structure of low attenuation.
Focal enhancement, also known as focal banding, is the increased intensity
in the focal region that appears as a brightening of the echoes on the display.
Mirror imaging artifact is most commonly seen around the diaphragm; this
artifact results from sound reflecting off another reflector and back.
Mirroring is the appearance of artifacts on a spectral display when there is
improper separation of forward and reverse signal processing channels.
Consequently, strong signals from one channel mirror into the other.
Multi-path positioning and refraction artifacts describe the situation in which
the paths to and from a reflector are different. The longer the sound takes
traveling to or from a reflector, the greater the axial error in reflector positioning
(increased range). Refraction and multi-path positioning errors are normally
relatively small and contribute to general degradation of the image rather than
to gross errors in object location.
Propagation speed errors occur when the assumed value for propagation
speed by the ultrasound system is incorrect. If the actual speed is greater than
that assumed, the calculated distance to a reflector is too small, and the reflector
iU22 User Manual
204
4535 614 45861
Transducers
8
To Next Page
Loading...
