Chapter 12 Ultrasound Physics (Image artifacts) Questions and answers
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Course
Sonography
Institution
Sonography
What is an artifact?
not true representation of our patients anatomy
or
a structure in the image that does not correlate directly with actual tissue
Artifacts include
missing reflectors
structures not representative of tissue
spatial misregistration of reflectors
In other words ...
Chapter 12 Ultrasound Physics
(Image artifacts) Questions and
answers
What is an artifact? - answer not true representation of our patients
anatomy
or
a structure in the image that does not correlate directly with actual
tissue
Artifacts include - answer missing reflectors
structures not representative of tissue
spatial misregistration of reflectors
In other words artifacts include - answer reflections that are not
real, not seen on the image, incorrect size/shape, incorrect position
and incorrect brightness
Artifacts occur because an - answer error occurs somewhere in the
process of obtaining the image
Causes of artifacts include - answer acoustic properties of tissues
technical limitations
equipment malfunction
Some artifacts can be and need to be - answer resolved others need
to be recognized so misdiagnoses are NOT made
,Assumptions of imaging systems - answer assumptions the machine
has to make in order to create images.
These assumptions are often contradicted by - answer the way in
which the sound beam actually behaves in tissue
This contradiction results in - answer errors in the presentation of
the echo information.
Most artifacts are explained by - answer identifying which
assumptions were violated during image creation
What are the first 4 assumptions of imaging systems - answer 1)
sound wave travels in a straight line path directly from transducer
to reflector and back to the transducer
2) attenuation of sound wave in tissue is uniform along the path
3) beam dimensions are small in both section thickness and lateral
directions
4) all detected echoes originate from the axis of the main beam only
What are the other 4 assumptions of imaging systems - answer 5)
all received echoes are derived from the most recently transmitted
pulse
6) sound wave travels in tissue at exactly 1540 m/s
7) each reflector contributes a single echo when it's interrogated
along single scan line
8) the induced echo signal is derived from a single object and is
directly related to its reflective properties
All of these assumptions do not always occur, sometimes.._______ -
answer the pulse bounces around before returning to the
transducer
, Also sound does not always.._____ - answer travel at 1540 m/s, this is
just an average the sound travels through soft tissue
A depth of _________ corresponds to a time of __________, 1 way. -
answer 1cm
13 microseconds
The sound waves are encountering different types of tissue and
moving at different velocities creates - answer artifacts
partial volume artifact - answer the assignment of an intermediate
signal level when the sound beam encompasses objects with
different acoustic properties
partial volume artifacts are also called - answer slice thickness
artifacts or section thickness artifacts
Partial volume artifacts are related to - answer the dimensions of
the beam
With partial volume artifacts what happens?? - answer artifactual
echoes are placed inside fluid filled structures (incorrectly
postioned)
Partial volume artifact occurs because the - answer beam is not thin
enough to encounter tissue or fluid located at the center of the
beam.
The beam is thinnest in the - answer focal zone
Different types of transducers produce - answer thinner beams
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