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Spreading out of a sound wave from a small source
What is divergence
Small
Would a bigger or smaller source have more divergence
Fire a group of elements together to create a wave front
How did Huygen's principle teach us to limit divergence
Non-uniform
What kind of beam uniformity do near fields have
Interference
What causes the beam uniformity to be non-uniform in near fields
Uniform
What kind of beam uniformity do far fields have
Low Q
What can also make the near field less uniform
Intensity differences
What else can the non-uniformity of the near field be related to/represented
Off axis beams
What are grating lobes
Main beam
Do the grating lobes or main beam contain most of the energy
True
T/F: the grating lobes are weaker than the main beam
Main beam
What is 1
Grating lobes
What is 2
Side lobes
What are the grating lobes called in mechanical probes
Cross talk from length and width vibration
What are the grating lobes a result of
Radial mode vibration in the single disc probes
What are the side lobes a result of
Fresnel
What is another name for the near field
Fraunhofer
What is another name for the far field
Nearly constant beam width
What is the near field characterized by
Divergent beam width
What is the far field characterized by
True
T/F: even with old flats disc there is a natural narrowing of the beam
One near field length
Where does the natural narrowing of the beam occur in old flat disc probes
Transition zone
What is the point called where there is a natural narrowing of the beam one near field length
One half the crystal diameter
How big is the beam at the transition zone
2 NZL
What is the measurement of 1
1 NZL
What is the measurement of 2
1/2 crystal diameter
What is the measurement of 3
1 of crystal diameter
What is the measurement of 4
Usable beam shape
What does the natural beam shape define
2 NZL
What is the length of the beam equal to
Reasonable lateral resolution
What does the length of the beam (2 NZL) provide
NZL = D^2 / 4 x wavelength
What is the formula to calculate the near field
NZL = D^2 x f / 6
How is the formula to calculate the near filed rewritten for soft tissue
So does the NZL
In the NZL formula, as frequency or diameter of the crystal increases:
Divergent part of the beam
The far field or the Fraunhofer zone is the:
Sin 0 = 1.22 x wavelength / D
What is the formula used to calculate the amount of divergence
Decrease the angle of divergence
What does increasing the frequency or diameter of the crystal do in the amount of divergence equation
2
Which beam has a bigger diameter and a smaller angle of divergence
2
Which beam most likely has a higher frequency
How many crystals that are going to fire in a group to manipulate the diameter
What is a simple description of aperture
False, was only considering single disc probes
T/F: the previous diameter principles were considering BOTH single disc and array probes
Aperture
What is diameter controlled by in the array probe
Increases
What happens to aperture as the depth of focus increases
To maintain relatively consistent beam width
Why does aperture increase as depth of focus increases
3
Which has more aperture
Improve lateral resolution
What is the prime reason for focusing
Decreasing beam width
What are we doing to the beam when focusing
Improves sensitivity
What else does decreases the beam width do while focusing
Near field only
Can you focus the near field, far field, or both
Mechanical and electronic
What are the two different types of focusing
Internal and external
What are the two types of mechanical focusing
Curve is applied to the crystal
When does internal focusing occur
Curve in a pair of glasses
What is the curve of the crystal in internal focusing analogous to
Acoustic lens or mirror
What are the two ways external focuses is accomplished
Acoustic lens
What kind of external focusing is 1
Mirror
What kind of external focusing is 2
It is fixed
What is the nature of the focus in older single crystal probes
Short, medium, long
What are the three categories that mechanical probes can be categorized into
Focal lengths
What are the categories short, medium, and long based on
1-4cm
What is the focal length range for the short category
4-10cm
What is the focal length range for the medium category
7-19cm
What is the focal length for the long category
Array transducers
What probes is electronic focusing found in
Transmit focusing
What should electronic focusing be referred to as
It is variable and operator controlled
What is the nature of electronic focusing
Flat single disc
How do the elements act is there are excited at the same time
Focus
Applying delays to the crystal can steer and ______ the probe
Increase
Increasing the delays will ______________ the focus
Focal region
What do the wave fronts converge toward when time delays are used to excite a group of elements
Lens or curved element
The wave fronts converging toward the focal region when excited using delays is similar to :
Lateral resolution improves
What is the advantage of using focus
Divergence in far field increases and NZL will decrease
What are the disadvantages of using focus
Dynamic aperture and frequency
What can be used to overcome the disadvantages of focus
Machine
Do we need to change the dynamic aperture or does the machine usually do this for us
We have to change it
Do we need to change the frequency or does the machine does this for us automatically
Use of both mechanical and electronic focusing
What is dual focusing
3D
Is the beam 2D or 3D
Z-axis
What is another axis that we usually don't consider
Elevational plane
What is another name for the z-axis
Mechanical focus
What focus is used on the z-axis
False
T/F: the z-axis is a consistent thickness
Natural z-axis focus
What does the natural converge and diverge of the z-axis result in
May not be at the ideal spot
What is the negative of the natural z-axis focus
Manipulates where the z-axis focus is
How does mechanical focus used on the elevational plane
True
T/F: you can get artifacts from the elevational plane
Cystic structure that is smaller than the beam gets echoes from behind/in front of it that looks like they are in the cyst
Explain how you get artifacts from the elevational planes
Elevational
What thickness is 1
Lateral
What thickness is 2
Axial
What thickness is 3
Thickness of beam
What is lateral related to
SPL
What is axial related to
True
T/F: it is possible to have more than one transmit focus on the image
Better lateral resolution throughout image
What is the advantages of multiple focus
Decreases frame rate
What is the disadvantage of multiple focus
Because the transducer has to wait for all of the scan lines to return before getting an image
Why does multiple focus decrease frame rate
Thyroid
When is it okay to have multiple focus
Echo and OB
What are some examples of when it is never okay to have multiple focus
Long fucs
What does expanding the focal regions of the transducer result in
True
T/F: array transducers can also focus the received echo signals
Time delays are applied to the received echoes to allow for constructive interference
How do array transducers focus the received echo signals
Note 
Flashcard (34)