Flashcards in DMS 120 - PHYSICS MIDTERM Deck (64):

1

## Interfaces that scatter ultrasound energy are usually considered to be...

### those that are equal to or smaller than the wavelength.

2

## Regions of lower pressure and density are called...

### RAREFACTIONS

3

## If you switch to a lower frequency for penetration, the wavelength of the transducer will...

### increase

4

## The attenuation of a 5.0-MHz transducer at a depth of 4 cm is ____ dB.

### 10.0 dB

5

##
The higher the transducer frequency, the higher the...

### Rayleigh Scattering

6

##
The following are all ultrasound frequencies except:

### 15.0 kHz

7

## The duty factor will increase with all of the following :

###
- pulse repetition frequency.

- pulse duration.

- period.

8

## The attenuation of a 5-MHz transducer in soft tissue would be...

### 5.0 dB at 2 cm of depth

9

## What is the period of a 5.0-MHz transducer in soft tissue?

### 0.2 µs

10

##
Impedance is equal to density multiplied by:

### propagation speed

11

##
Continuous wave Doppler has a duty factor of ____ %.

### 100

12

##
For perpendicular incidence, the incidence angle is ___ degrees.

### 90

13

##
Attenuation decreases with an increase in:

### wavelength

14

##
The average propagation speed in human soft tissue is ____.

###
1.54 mm/µs

15

##
Frequency is _____ proportional to wavelength.

### inversely

16

## The distance to a reflector in soft tissue is 15 cm. What is the round-trip time to this depth?

###
195.0 µs

17

##
Period is the ____ it takes for one ____ to occur.

###
time; cycle

18

## In oblique incidence the sound is refracted at a boundary between ____ where propagation speeds are different.

### two media

19

##
The propagation speed in soft tissue is not:

### 1.54 m/s.

20

## ____ Law relates the transmitted beam direction to the incident beam direction and the speeds of sound in the two materials forming the interface.

### Snell's

21

##
The pulse repetition frequency is the number of pulses that occur in a ____.

###
second

22

##
When frequency increases, the period...

### decreases.

23

##
Amplitude is the maximum variation that occurs in an acoustic ____.

### variable

24

##
3 dB of attenuation means?

### One half the original intensity.

25

##
If beam power increases, intensity will...

### increase

26

##
Propagation speed is the speed at which a wave:

### travels through a medium.

27

##
Sound is a ____ longitudinal wave.

### mechanical

28

##
The wavelength of 3-MHz ultrasound in soft tissue is ____

### 0.51 mm

29

##
CW sound is NOT described by:

### pulse duration

30

##
____ is the number of complete cycles per second.

### Frequency

31

##
As sound travels, the reduction in amplitude and intensity of the wave is called:

###
attenuation

32

##
Propagation speed is higher or lower in bone than soft tissue?

### Higher

33

##
Sound requires a ___ through which to travel.

### medium

34

##
Ultrasound pulses contain a range of frequencies called the ____.

###
bandwidth

35

##
Duty factor is:

### unitless.

36

##
The spatial pulse length will not increase with:

### frequency

37

##
The propagation speed for a round-trip time of 39 µs is ____ mm/µs.

A. 1540.0

B. 15.4

C 1.45

### NONE OF THE ABOVE

38

##
Cycle, period, and frequency are examples of acoustic ____

### parameters.

39

##
The fraction of time that pulsed ultrasound is on is called ____.

###
duty factor

40

##
Pulse repetition frequency is the ____ of pulses occurring in 1 second.

### number

41

##
Attenuation is higher OR lower in bone than in soft tissue?

### higher

42

##
Compression is not an _____.

### acoustic variables

43

##
The best way to describe the role of ultrasound scattering in diagnostic imaging is:

### that it allows us to see the tissue interfaces .

44

##
The distance to the reflector in soft tissue with a round-trip time of 39 µs is:

### 30 mm or 3 cm.

45

##
If the beam area decreases, the intensity will____.

### increase

46

##
The four intensity values from the greatest to the least are:

###
SPTP, SATP, SPTA, SATA.

47

##
Heat production depends most directly on the ____ intensities.

### SPTA

48

##
Pulsed wave ultrasound is not described by the terms such as:

### frequency, wavelength, and propagation speed

49

##
The rate at which energy passes through a unit area is called _____.

### power

50

## If the density of medium 2 is 10% greater than that of medium 1 and the propagation speeds are equal, the impedance of medium 2 is ____ for medium 1.

###
20% higher

51

##
Propagation speed is primarily determined by the ____ of the medium.

### stiffness

52

##
The unit for impedance is:

### rayls

53

##
In oblique incidence the incidence and reflection angles are always:

### equal

54

##
If frequency increases, period will _____.

### decrease

55

##
Stiffer media have higher or lower sound speeds?

### higher

56

##
Intensity is equal to the power of:

### a wave divided by the area over which the power is spread.

57

##
20 kHz is equal to...

### 20,000 Hz.

58

##
500 Hz is equal to...

### 0.500 kHz.

59

##
TRUE OR FALSE

Stiffer media have higher sound speeds.

### TRUE

60

##
TRUE OR FALSE

The impedances of the media determine how much of the incident sound wave is reflected and transmitted into the second medium.

### TRUE

61

##
Attenuation encompasses:

###
- absorption.

- scattering.

- reflection.

62

##
TRUE OR FALSE

Spatial pulse length is determined by the length of the pulse and the propagation speed.

### FALSE

63

##
Impedance increases when ____ increases.

###
Density and propagation speed

64