User's Manual

Table Of Contents
InnoSight Ultrasound System
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 Acoustic artifacts
108
P6992-4, EN, 16/12/6
Acoustic saturation occurs when received signals reach a systems 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 channelsConsequently, 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 reflect or from the echo arrival time assuming that
all echoes were generated by the last emitted pulse The maximum depth to be imaged unambiguously by
the system determines its maximum pulse repetition frequency
Reverberation is the continuing reception of a particular signal because of reverberation rather than
reflection from a particular acoustic interface This phenomenon is analogous to the effect created by
mirrors positioned on opposite walls when an object, a head for instance, is placed between the mirrors
The image of the head is reflected back and forth infinitely between the two mirrors, creating the optical
illusion of multiple heads Reverberations are easily identifiable, because they are equally spaced on the
display
Scattering is the diffuse, low-amplitude sound waves that occur when acoustic energy reflects off tissue
interfaces smaller than a wavelength In diagnostic ultrasound, Doppler signals come primarily from
acoustic energy back-scattered from red blood cells
Shadowing is the reduction in echo amplitude from reflectors that lie behind a strongly reflecting or
attenuating structureThis phenomenon occurs when scanning a lesion or structure with an attenuation
rate higher than that of the surrounding tissueThe lesion causes a decrease in beam intensity, which
results in decreased echo signals from the structures beyond the lesion Consequently, a dark cloud behind
the lesion image forms on the display This cloud, or shadow, is useful as a diagnostic clue
Side lobes (from single-element transducers) and grating lobes (from array transducers) cause objects that
are not directly in front of the transducer to be displayed incorrectly in lateral position