Physics review Test 2

Question 1

What happens to sound waves as they propagate in a medium?

Answer 1

They weaken.

Question 2

What does attenuation mean ?

Answer 2

The loss of energy. Decrease in intensity, power and amplitude.

Question 3

What two factors is attenuation determined by ?

Answer 3

Path length

Frequency of sound.

Question 4

How are distance and attenuation related?

Answer 4

They are directly related.

Question 5

How are frequency and attenuation related?

Answer 5

They are directly related.

Question 6

What is attenuation measured in ?

Answer 6

Db

Question 7

The more attenuation you have, the _______ the distance and the higher the _______.

Answer 7

Longer, frequencies.

Question 8

The less attenuation you have, the _______ the distance and the lower the ________.

Answer 8

shorter, frequencies.

Question 9

What three processes contribute to attenuation ?

Answer 9

reflection, scattering, absorption.

Question 10

As a sound strikes a boundary, a portion of the wave’s energy may be redirected or _______.

Answer 10

Reflected

Question 11

Name two forms of reflection.

Answer 11

specular & diffuse

Question 12

What type of reflection is smooth, and reflected only in one direction in an organized manner?

Answer 12

Specular reflection.

Question 13

Name one limitation for a specular reflector.

Answer 13

once the wave is slightly off axis, the reflection does not return to the transducer.

Question 14

When a wave reflects off an irregular surface, it radiates in more than one direction, this form of reflection is called ________.

Answer 14

diffuse reflection or backscatter.

Question 15

What is an advantage of diffuse reflections ?

Answer 15

interfaces at sub optimal angles to the sound beam can still produce reflections that will return to the transducer.

Question 16

What is a disadvantage of diffuse reflections?

Answer 16

they have a lower strength than specular reflections.

Question 17

What is scattering in ultrasound ?

Answer 17

the random redirection of sound in many directions.

Question 18

What scatters more, higher frequency sound beams or lower?

Answer 18

Higher frequency.

Question 19

How is scattering related to frequency?

Answer 19

directly related.

Question 20

When does Rayleigh scattering happen?

Answer 20

occurs when the structures dimensions are much smaller than the beam’s wavelength.

Question 21

In clinical imaging, the interaction of ultrasound and red blood cells results in ___________.

Answer 21

Rayleigh scattering

Question 22

Mathematically, scattering is related to frequency raised to the ______ power.

Answer 22

fourth

Question 23

what type of reflection sends sound back to the transducer, and is organized?

Answer 23

specular reflection.

Question 24

What type of reflection sends sound back to the transducer but is disorganized?

Answer 24

diffuse or backscatter.

Question 25

What type of reflection sounds sound in all directions, and is organized?

Answer 25

Rayleigh scattering.

Question 26

What type of reflector sends sound in all directions and is disorganized?

Answer 26

Scattering.

Question 27

What is the third and most sizeable component of attenuation ?

Answer 27

absorption

Question 28

what is absorption?

Answer 28

occurs when ultrasonic energy is converted into another energy, such as heat.

Question 29

How do you report attenuation, in ultrasound?

Answer 29

by calculating attenuation coefficient

Question 30

What is the attenuation coefficient ?

Answer 30

is the number of decibels of attenuation that occurs when sound travels one cm.

Question 31

What are the units of attenuation coefficient?

Answer 31

db/cm

Question 32

What is the equation for total attenuation?

Answer 32

total attenuation= attenuation coefficient (db/cm) * distance (cm)

Question 33

What is half-value layer thickness?

Answer 33

is the distance that sounds travel in a tissue that reduces the intensity of a sound to one-half its original value.

Question 34

Whats another way that half-value layer thickness can be described ?

Answer 34

depth of a tissue that results in 3 db of attenuation to the intensity.

Question 35

The half- value layer is _____ for tissues that attenuate sound a great deal, such as lung or bone.

Answer 35

thin

Question 36

high frequency sound results in a _____ half-value layer.

Answer 36

thin

Question 37

Lower frequency sound results in a _____ half-value layer.

Answer 37

Thick

Question 38

In clinical imaging half- value layers ranges from ___ to ___.

Answer 38

0.25 to 1.0 cm.

Question 39

What other names are half value layer known by

Answer 39

Penetration depth, depth of penetration, half-boundary layer.

Question 40

The half -value layer thickness depends on what two factors?

Answer 40

the medium and the frequency of sound

Question 41

What is impedance ?

Answer 41

Acoustic resistance to sound traveling in a medium.

Question 42

How do you calculate impedance ?

Answer 42

Z= P*C

Question 43

Reflection of an ultrasound wave depends upon what differences?

Answer 43

the difference in acoustic impedance's of the two media at a boundary.

Question 44

Impedance is determined by the ________ only.

Answer 44

Medium

Question 45

Acoustic impedance is also called __________.

Answer 45

characteristic impedance

Question 46

Impedance is reported in the units of _________.

Answer 46

rayls

Question 47

What does normal incidence mean ?

Answer 47

That the incident sound beam strikes the boundary at exactly 90 degrees.

Question 48

What does oblique incidence mean ?

Answer 48

That the incident sound beam strikes the boundary at any angle other than 90 degrees.