Ch. 9 Physics: Sound Beams

Question 1

As sound travels, the width of the beam______

Answer 1

changes

Question 2

How does the beam change?

Answer 2

Begins the same diameter as the transducer (aperture)

Narrows progressively

Then expands again

Question 3

What are the zones of the beam?

Answer 3

Near zone

focus

focal zone

far zone

Question 4

What is another name for the near zone?

Answer 4

Fresnel zone

Question 5

The region from the transducer to the focus.

Answer 5

near zone or fresnel zone

Question 6

The sound beam is at its most narrow in this section of the beam?

Answer 6

Focus or focal point

Question 7

Structures imaged at this point are the highest quality and most accurate.

Answer 7

Focus or focal point

Question 8

How big is the focus of the original beam’s diameter?

Answer 8

one-half

Question 9

What section of the beam has the highest spatial peak intensity?

Answer 9

Focus

Question 10

Region from the focal point and beyond, also called the Fraunhofer zone.

Answer 10

Far zone

Question 11

True or false
At depths more than two near zones lengths, the beam is still the same size as the active element

Answer 11

False
At depths more than two near zones lengths, the beam is wider than the active element

Question 12

What happens to the beam after the focal point?

Answer 12

The beam diverges, or spreads out, after the focal point

Question 13

Which region is the most important region in diagnostic imaging, where the most accurate images are created?

Answer 13

Focal zone

Question 14

What is the exact center of the focal zone called?

Answer 14

Focus

Question 15

Also known as focal depth or near zone length.

Answer 15

Focal length

Question 16

The distance from the transducer to the focus, also is the length of the near zone.

Answer 16

Focal length

Question 17

The diameter of the crystal at the transducer face is 12 mm. The near zone length measures 8 cm. The focal zone is 4 cm long.

What is the diameter of the sound beam as it exits the transducer?

What would the beam diameter measure at 8 cm?

What would the beam diameter measure at 16 cm?

What distance would mark the beginning of the focal zone?

When would the beams diameter be larger than 12 mm?

Answer 17

• 12mm

-6mm

-12mm

-6 cm

-At a length greater than 16 cm, or after the second near zone length

Question 18

What are the two factors that effect the depth on fixed focus?

Answer 18

Transducer diameter (aperture)

Frequency of the sound beam

Question 19

Crystal diameter is _______ related to focal depth.

Answer 19

Directly

Question 20

Frequency is ________ related to focal depth.

Answer 20

Directly

Question 21

A smaller crystal diameter has a ______ focal depth.

Answer 21

Shallow

Question 22

A bigger crystal diameter has a ______ focal depth.

Answer 22

Deeper

Question 23

Low frequency has a _______ focal depth

Answer 23

shallow

Question 24

Higher frequency has a ______ focal depth

Answer 24

deeper

Question 25

What describes the gradual spread of the sound beam in the far field?

Answer 25

Divergence

Question 26

Is it more or less divergence that has better resolution in deeper tissues?

Answer 26

Less divergence

Question 26

Is it more or less divergence that has better resolution in deeper tissues?

Answer 26

Less divergence

Question 27

Divergence of the sound beam is _________ related to: Transducer diameter (aperture) Frequency of the sound beam

Answer 27

Inversely

Question 28

Smaller element diameter =________ divergence in the far field

Answer 28

Greater

Question 29

Larger element diameter = _________ divergence in the far field (improves lateral resolution deeper)

Answer 29

Less

Question 30

Lower frequency = _______ divergence in the far field

Answer 30

Greater

Question 31

Higher frequency = ______ divergence in the far field

Answer 31

Less

Question 32

Aperture (Beam) Diameter & Frequency of Sound are BOTH _________ RELATED to Divergence

Answer 32

Inversely

Question 33

Aperture (Beam) Diameter & Frequency of Sound are BOTH _________ RELATED to Depth

Answer 33

Directly

Question 34

Which of the following probes would create the most divergence? Small diameter, high frequency Large diameter, low frequency Large diameter, high frequency Small diameter, low frequency

Answer 34

Small diameter, low frequency

Question 35

Two 12MHz transducers have apertures measuring 6 mm and 9 mm. Which would have the best lateral resolution in the far field?

Answer 35

The 9 mm diameter – larger = less divergence

Question 36

Two 5 mm diameter crystals have frequencies of 4Mhz and 6MHz. Which will produce the most divergence?

Answer 36

4 MHz – lower = more divergence

Question 37

Which of the following probes would create the most divergence? 2 mm, 8 MHz 6 mm, 6 MHz 2 mm, 4 MHz 8 mm, 6 MHz

Answer 37

2 mm, 4 MHz

Question 38

True or False: Lateral resolution is inversely related to beam diameter?

Answer 38

True

Question 39

true or False: Larger diameter crystals have better lateral resolution than smaller crystals?

Answer 39

True

Question 40

Which of the following probes would create the shallowest focus? 3 MHz, 4 mm crystal diameter 3 MHz, 6 mm crystal diameter 6 MHz, 4 mm crystal diameter 6 MHz, 6 mm crystal diameter

Answer 40

3 MHz, 4 mm crystal diameter

Question 41

True or False: Frequency is directly related to focal depth

Answer 41

True

Question 42

True or False: Aperture diameter is directly related to focal depth

Answer 42

True

Question 43

True or False: Lower frequency transducers diverge more

Answer 43

True

Question 44

True or False: Smaller apertures diverge less

Answer 44

False

Question 45

Sound waves produced by very small sources (tiny pieces of PZT) and all diverge to form the shape of a V.

Answer 45

spherical waves diffraction patterns Huygen’s wavelets

Question 46

States that a large active element may be thought of as millions of tiny sound sources each producing its own V-shaped waves called wavelets.

Answer 46

Huygen's principle

Question 47

Explains that the shape of an imaging transducer’s sound beam is based upon the idea that in-phase and out-phase wavelets are interfering with each other.

Answer 47

Huygen's principle