DMS 120 - PHYSICS MIDTERM Flashcards Preview

DMS 120 & 122- PHYSICS & HEMODYNAMICS MIDTERM > DMS 120 - PHYSICS MIDTERM > Flashcards

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

Pulse duration will not increase with...

frequency