Acoustic Artifacts
The transducer adds its own signature to the echo information in the form of
beam width effects, axial resolution limitations, and frequency characteristics.
The control choices made by the sonographer that affect amplification, signal
processing, and echo signal display can lead to significant differences in the
displayed appearance of echo data. Following is a brief discussion of acoustic
artifacts. An understanding of the physical basis for the production of signals
displayed on ultrasound images is helpful in minimizing artifacts on images and
interpreting the results of studies.
An artifact is an echo displayed in a different position than its corresponding
reflector in the body. Artifacts can also be caused by intervening tissue properties.
Artifacts can originate from external noise, reverberations, multi-path reflections,
or misadjusted equipment. They can also come from the ultrasonic beam
geometry and unusual changes in beam intensity. Artifacts and their manifestations
are listed below, and following are some definitions of various artifacts.
• Added objects displayed as speckle, section thickness, reverberation, mirror
image, comet tail, or ring down
• Missing objects due to poor resolution
• Incorrect object brightness due to shadowing or enhancement
• Incorrect object location due to refraction, multi-path reflections, side lobes,
grating lobes, speed error, or range ambiguity
• Incorrect object size due to poor resolution, refraction, or speed error
• Incorrect object shape due to poor resolution, refraction, or speed error
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.
iE33 User Manual
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Transducers
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