Philips epiq 7, User Manual

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If you encounter poor image quality or transducer problems, see “Troubleshooting” on page
295 .
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. On the Color display an immediate
change in color from one Nyquist limit to the other is seen.
Acoustic Artifacts Transducers
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