Chapter 8: Artifacts
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Introduction
The term artifact has many different meanings even within the“nar-
row” field of ultrasound. The word artifact, defined as “something
made through skill by man,” is hardly the definition we would use
in ultrasound. In its simplest form, an artifact is any representation
in the image or on a spectrum which is not indicative of “truth”.
To quote Shakespeare and Socrates in a mixed metaphor of sorts,
“therein lies the rub for what is truth but a shadow on the cave wall.”
In other words, “truth” and artifact are often extremely difficult to
discern, and sometimes present only a shadow by which to deter-
mine “reality”. In essence, determining what is “real” is often more
nebulous than we would like to admit.
One thing is for sure, not all artifacts are bad. Paradoxically, some
artifacts can be very useful as an indication of a very specific
mechanism in the body. For example,the bright white“spike”which
occurs on the Doppler spectrum often referred to as a “valve click”
is in reality an artifact caused by circuit saturation. Yet, it is a useful
artifact when controlled since it helps to quickly identify timing in
the cardiac cycle. Artifacts such as shadowing and enhancement
can be very useful since understanding the mechanisms which
cause the artifact leads to information about the associated tissues
and structures. For example, shadowing may indicate the presence
of a calcification and enhancement may indicate the presence of a
fluid. Of course there are other artifacts which are absolutely not
useful such as susceptibility artifacts which result from receiving
radio frequency signals from outside sources. These signals from
sources such as radio signals, television signals, pulse oximeters,
Bovie electrosurgical units, etc., are not related to what is physically
occurring in the body and therefore are not at all useful as artifacts.
Throughout the entire book we have been discussing artifacts within
the context of each chapter topic. For example, we have already
discussed the concept of speed error when discussing the assumed
propagation velocity in Chapter 2, specular reflection as a main
source of imaging artifacts and refraction related artifacts when dis-
cussing attenuation in Chapter 3, range ambiguity when discussing
timing issues in pulsed wave operation in Chapter 4, grating lobes
when discussing transducer design in Chapter 5, contrast issues
and detail resolution in Chapter 6, and aliasing when discussing
Doppler in Chapter 7. In fact, many more artifacts were discussed,
but the list is making the previous sentence too long for anyone to
read. Great effort has been expended to make sure that the physics
of themechanisms which cause artifacts has been thoroughly taught
in the previous chapters so that this chapter on artifacts can simply
serve as a compilation of artifacts, rather than trying to teach all of
the underlying physics in one chapter. In other words, this chapter
presumes that the previous seven chapters have been read. Because
understanding artifacts requires some clinical background,the entire
chapter is Level 2. In an effort to make the integration of artifacts
easier,we will group artifacts either by commonmechanisms (source
of the artifact) or by common appearance attribute (location, inten-
sity, etc.). The result of this classification scheme is that the same
artifact may be listed inmore than one category. Additionally, there
are manymore artifact images included in the online animation and
image library,intended tomake identification of artifacts bothmore
comfortable and systematic.
KEY CONCEPT
1. Categorizing Artifacts
1.1 Image Detail Resolution Related
We have already discussed artifacts associated with ultrasound
beam characteristics generated by transducer and system designs.
These artifacts are often, but not always, the limiting factor in detail
resolution.
Detail resolution artifacts for 2D and color Doppler are associated
mainly with:
Artifacts
Chapter 8
