Ultrasound Physics - 10\sound Beams

Front 1

At the starting point, how wide is the sound beam width?

Back 1

The sound beam's width is the same as the transducer diameter

Front 2

As the sound beam gets further from the transducer, what happens to it?

Back 2

The sound beam narrows, like a funnel

Front 3

After the sound beam narrows, what happens to its shape?

Back 3

The sound beam expands

Front 4

What is the location where the beam diameter is the narrowest called?

Back 4

Focus or Focal Point

Front 5

What is the region from the transducer to the focus called?

Back 5

Near Zone
(aka Fresnel Zone)

Front 6

At the far end of the near zone, what is the diameter of the near zone?

Back 6

1/2 the diameter of the active element

Front 7

The distance from the transducer to the focus is called what?

Back 7

Focal Length
(aka Focal Depth or Near Zone Length)

Front 8

The region starting at the focus and extending deeper is called what?

Back 8

Far Zone
(aka Fraunhoffer Zone)

Front 9

When the beam is two near zone lengths from the transducer, how wide is it?

Back 9

The beam is as wide as the active element again

Front 10

What happens to the sound beam width beyond two near zone lengths from the transducer?

Back 10

The beam widens beyond the width of the active element, and continues expanding

Front 11

The region around the focus where the beam is relatively narrow is called what?

Back 11

Focal Zone

Front 12

Why is the focal zone important to sonographers?

Back 12

Reflections arising from the focal zone create images of superior detail, compared to other depths

Front 13

What marks the end of the near zone?

Back 13

Focus

Front 14

At what point does the sound beam first begin to widen?

Back 14

Focus

Front 15

The focal zone is found where?

Back 15

Half in the near zone
Half in the far zone

Front 16

The distance from the transducer to the focus is called what?

Back 16

Focal Depth
(aka Focal Length or Near Zone Length)

Front 17

Is focal depth adjustable by sonographers on most modern ultrasound systems? If so, what is this called?

Back 17

Yes. Adjustable focus systems are called Phased Array

Front 18

For a fixed-focus transducer, what two characteristics determine the focal depth?

Back 18

1. Transducer Diameter
2. Sound Frequency

Front 19

What is the relationship between transducer diameter and focal depth?

Back 19

Directly Related

Front 20

What is the relationship between frequency and focal depth?

Back 20

Directly Related

Front 21

High frequency transducers are used to image superficial, or shallow structures. How can this be when a high frequency beam will produce a deep focus (direct relationship)?

Back 21

Transducer manufacturers overcome this by making exceptionally small diameter crystals for high frequency transducers in order to locate the focus shallower for superior images

Front 22

The gradual spread of the sound beam beyond the focus is called what?

Back 22

Beam Divergence

Front 23

What two characteristics of a transducer determine beam divergence?

Back 23

1. Transducer Diameter
2. Sound Frequency

Front 24

What is the relationship between crystal diameter and beam divergence?

Back 24

Inversely Related

Front 25

(Smaller|Larger) crystals produce beams that spread out (more|less) in the far field

Back 25

Small|more
Larger|less

Front 26

Since larger diameter crystals create sound beams that diverge less in the far field, what would be improved in the far field?

Back 26

Lateral Resolution

Front 27

What is the relationship between frequency and beam divergence?

Back 27

Inversely Related

Front 28

Since high frequency sound beams diverge less in the far field, what would be improved in the far field?

Back 28

Lateral Resolution

Front 29

Less divergence involves what two characteristics?

Back 29

1. Larger Diameter (PZT)
2. Higher Frequency

Front 30

More divergence involves what two characteristics?

Back 30

1. Smaller Diameter (PZT)
2. Lower Frequency

Front 31

Shallow focus involves what two factors?

Back 31

1. Smaller Diameter (PZT)
2. Lower Frequency

Front 32

Deep focus involves what two characteristics?

Back 32

1. Larger Diameter (PZT)
2. Higher Frequency

Front 33

Very small pieces of PZT are called what?

Back 33

Huygens' Sources

Front 34

Very small pieces of PZT create sound waves in the shape of a "V" called what?

Back 34

Spherical Waves
Diffraction Patterns
Huygens' Wavelets

Front 35

This explains the shape of an imaging transducer's beam based upon in-phase and out-of-phase wavelets interfering with each other

Back 35

Huygens' Principle

Front 36

Accuracy in imaging is called what?

Back 36

Resolution

Front 37

The ability to distinctly identify two structures that are very close together when the structures are side-by-side, or perpendicular to the beam's main axis

Back 37

Lateral Resolution

Front 38

This answers the question: What is the minimum distance that two structures, positioned side-by-side, can be apart and still produce two distinct echoes on an ultrasound image?

Back 38

Lateral Resolution

Front 39

LATERAL RESOLUTION: units?

Back 39

Distance (mm, cm, etc)

Front 40

LATERAL RESOLUTION: determined by?

Back 40

Width of the sound beam

Front 41

How does a sonographer improve image resolution?

Back 41

Adjust depth; beam diameter varies with depth & a narrower beam has better resolution

Front 42

Synonyms for Lateral Resolution?

Back 42

Lateral
Angular
Transverse
Azimuthal

Front 43

Which type of resolution is superior in clinical imaging systems: lateral or axial resolution?

Back 43

Axial Resolution because pulses are shorter than they are wide

Front 44

When two reflectors are closer side-by-side than the beam width, what will be observed in the image?

Back 44

One reflector, instead of two (suboptimal lateral resolution)

Front 45

What are the advantages of using a high frequency transducer?

Back 45

Axial resolution is improved due to its shorter pulses.

Lateral resolution is improved due to its pulses diverging less in the far field

Front 46

What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with a lens?

Back 46

External Focusing

Front 47

What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with a curved active element?

Back 47

Internal Focusing

Front 48

What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with the ultrasound system's electronics?

Back 48

Phased Array Focusing

Front 49

Which focusing technique(s) can be used with single element transducers? array transducers?

Back 49

Single Element Transducers = External & Internal Focusing

Array Transducers = Phased Array Focusing

Front 50

External & internal focusing techniques are both called what?

Back 50

Fixed Focusing
Conventional Focusing
Mechanical Focusing

Front 51

What is a limitation to fixed focusing?

Back 51

Focal depth and the extent of focusing cannot be changed

Front 52

What four things happen to a beam when it is focused?

Back 52

1. Beam diameter in near field and focal zone is reduced
2. Focal depth is shallower
3. Beam diameter in the far zone increases
4. Focal zone is smaller

Front 53

Continuous Wave Frequency: determined by?

Back 53

Electrical frequency from ultrasound system

Front 54

Pulsed Wave Frequency: determined by?

Back 54

1. PZT thickness
2. Speed of sound through PZT

Front 55

Focal Length: determined by?

Back 55

1. PZT diameter
2. Sound Frequency

Front 56

Beam Divergence: determined by?

Back 56

1. PZT diameter
2. Sound Frequency

Front 57

Lateral Resolution: determined by?

Back 57

Beam Width