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
will be displayed too far from the transducer. Speed error can cause a structure
to be displayed with incorrect size and shape.
Range ambiguity can occur when reflections are received after the next pulse
is transmitted. In ultrasound imaging, it is assumed that for each pulse produced,
all reflections are received before the next pulse is sent out. The ultrasound
system calculates the distance to a reflector from the echo arrival time assuming
that all echoes were generated by the last emitted pulse. The maximum depth
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iE33 User Manual
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8
Transducers
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