Chapter 21 Part 2 Flashcards
T or F
Lobe artifact degrades lateral resolution
True
________ artifact appears when sound energy is transmitted in a direction other than along the beams main axis.
Lobe
T or F
Lobes are weaker than the primary beam and do not typically create reflections that appear on an image.
True
What are the 2 characteristics of lobe artifact?
- a second copy of the true reflector
- the artifact and the true reflector are located side by side at the same depth
What are lobes called when created by a single crystal transducer, such as a mechanical probe?
Side lobes
What are lobes called when created by array transducers?
Grating lobes
A process of dividing each PZT element into small pieces is called?
Subdicing
_________ lobe artifact can be reduced by subdicing
Grating
T or F
Grating lobes can be further reduced by exciting the subdiced elements with different voltage
True
Elements closer to the center of the sound beam are excited with higher voltages, while the outermost elements are excited with lower voltages. This process is called?
Apodization
2 methods to eliminate lobes
- Subdicing
- Apodization
What artifact is created when a sound pulse changes direction during transmission?
Refraction
Refraction is transmission with a _________.
Bend
T or F
Refraction artifact degrades lateral resolution
True
What are the 2 characteristics of refraction?
- a second copy of the reflector
- the copy is side by side, or at the same depth as the true reflector
What are two other names for slice thickness?
- section thickness artifact
- partial volume artifact
Slice thickness artifact is related to the dimension of the _________ that is perpendicular to the imaging plane.
Beam
_________ is determined by the thickness of the imaging plane.
Elevational resolution
The _______ reflector lies either above or below the assumed imaging plane, but is displayed within the image.
True
T or F
Slice thickness artifact fills in hollow structures such as cysts.
True
Slice thickness artifact is _______ (increased or reduced) with thinner imaging planes, such as those created by one half dimensional array transducers.
Reduced
________ resolution artifact occurs when a pair of side-by-side reflectors are closer than the width of the sound beam.
Lateral
T or F
In regards to lateral resolution, the reflectors are positioned perpendicular to the beam.
true
With lateral resolution, two objects appear as ______ reflection on the image.
one
Lateral resolution artifact may display a small reflector as a __________ rather than a narrow dot.
wide line
What is another name for lateral resolution artifact?
point spread artifact
T or F
Lateral resolution artifact is most likely to occur where the beam is smallest.
false
T or F
lateral resolution is least likely to occur at focus where beam diameter is smallest.
true
_________ resolution artifact is created when a long pulse strikes two closely spaced structures, where one is in front of the other.
Axial
With axial resolution artifact, the structures are __________ to the beam’s main axis.
parallel
T or F
Axial resolution artifact creates one reflection on the image from two closely spaced reflectors.
true
T or F
Transducers that create long pulses minimize axial resolution.
false
What artifact is created when sound pulses glance off a second structure on the way to or from the primary reflector?
Multipath artifact
What type of reflectors redirect sound waves in directions other than back toward the transducer?
Curved or oblique
The ability to precisely locate a moving structure at all times is called?
Temporal resolution
Temporal resolution is best with high or low frame rates?
high frame rates
Spatial resolution is related to the ___________ in an image.
overall detail
What are the factors that spatial resolution is determined?
- line density
- axial resolution
- lateral resolution
When is spatial resolution exceptional?
with high line density (closely packed sound pulses)
When is spatial resolution poor?
with low line density (wider gaps between the sound pulses)
When image information is displayed on a monitor, spatial resolution is affected by the number of ____________ scan lines per frame.
horizontal
T or F
More lines on a monitor provide better spatial resolution.
True
When the image information is in digital form, spatial resolution is related to __________.
pixel density
T or F
Higher pixel density results in better spatial resolution.
true
What artifact occurs when the pixel size is greater than the size of the reflector?
Spatial resolution artifact
What artifact occurs when a reflecting structure is located deeper than the imaging depth of the image?
Range ambiguity artifact
Range ambiguity artifact is eliminated by ________ (increasing or decreasing) the pulse repetition period.
increasing
What appears as small amplitude echoes and results from many sources, including electrical interference, signal processing, and spurious reflections?
Noise
T or F
Noise is more likely to affect low-level hypoechoic regions rather than bright echogenic areas.
true
Noise resulting from the constructive and destructive interference of small sound wavelets is known as?
acoustic speckle
____________ interference occurs when wavelets are in-phase.
Constructive
____________ interference occurs with out of phase wavelets.
Destructive
______________ is an effective tool to reduce speckle.
Spatial compounding
Another form of noise, with the presence of false echo signals arising from locations outside of the main sound beam is?
Clutter
Side lobes, grating lobes, and section thickness artifact are sources of _________.
Clutter
What reduces an image’s noise content?
Harmonic imaging
What is the goal of harmonic imaging?
To selectively distinguish meaningful reflections from noise, increasing the signal to noise ratio
