DMS 120 - PHYSICS MIDTERM

Question 1

Interfaces that scatter ultrasound energy are usually considered to be…

Answer 1

those that are equal to or smaller than the wavelength.

Question 2

Regions of lower pressure and density are called…

Answer 2

RAREFACTIONS

Question 3

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

Answer 3

increase

Question 4

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

Answer 4

10.0 dB

Question 5

The higher the transducer frequency, the higher the…

Answer 5

Rayleigh Scattering

Question 6

The following are all ultrasound frequencies except:

Answer 6

15.0 kHz

Question 7

The duty factor will increase with all of the following :

Answer 7

• pulse repetition frequency.
• pulse duration.
• period.

Question 8

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

Answer 8

5.0 dB at 2 cm of depth

Question 9

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

Answer 9

0.2 µs

Question 10

Impedance is equal to density multiplied by:

Answer 10

propagation speed

Question 11

Continuous wave Doppler has a duty factor of ____ %.

Answer 11

100

Question 12

For perpendicular incidence, the incidence angle is ___ degrees.

Answer 12

90

Question 13

Attenuation decreases with an increase in:

Answer 13

wavelength

Question 14

The average propagation speed in human soft tissue is ____.

Answer 14

1.54 mm/µs

Question 15

Frequency is _____ proportional to wavelength.

Answer 15

inversely

Question 16

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

Answer 16

195.0 µs

Question 17

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

Answer 17

time; cycle

Question 18

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

Answer 18

two media

Question 19

The propagation speed in soft tissue is not:

Answer 19

1.54 m/s.

Question 20

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

Answer 20

Snell’s

Question 21

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

Answer 21

second

Question 22

When frequency increases, the period…

Answer 22

decreases.

Question 23

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

Answer 23

variable

Question 24

3 dB of attenuation means?

Answer 24

One half the original intensity.

Question 25

If beam power increases, intensity will...

Answer 25

increase

Question 26

Propagation speed is the speed at which a wave:

Answer 26

travels through a medium.

Question 27

Sound is a ____ longitudinal wave.

Answer 27

mechanical

Question 28

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

Answer 28

0.51 mm

Question 29

CW sound is NOT described by:

Answer 29

pulse duration

Question 30

____ is the number of complete cycles per second.

Answer 30

Frequency

Question 31

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

Answer 31

attenuation

Question 32

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

Answer 32

Higher

Question 33

Sound requires a ___ through which to travel.

Answer 33

medium

Question 34

Ultrasound pulses contain a range of frequencies called the ____.

Answer 34

bandwidth

Question 35

Duty factor is:

Answer 35

unitless.

Question 36

The spatial pulse length will not increase with:

Answer 36

frequency

Question 37

The propagation speed for a round-trip time of 39 µs is ____ mm/µs. A. 1540.0 B. 15.4 C 1.45

Answer 37

NONE OF THE ABOVE

Question 38

Cycle, period, and frequency are examples of acoustic ____

Answer 38

parameters.

Question 39

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

Answer 39

duty factor

Question 40

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

Answer 40

number

Question 41

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

Answer 41

higher

Question 42

Compression is not an _____.

Answer 42

acoustic variables

Question 43

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

Answer 43

that it allows us to see the tissue interfaces .

Question 44

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

Answer 44

30 mm or 3 cm.

Question 45

If the beam area decreases, the intensity will____.

Answer 45

increase

Question 46

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

Answer 46

SPTP, SATP, SPTA, SATA.

Question 47

Heat production depends most directly on the ____ intensities.

Answer 47

SPTA

Question 48

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

Answer 48

frequency, wavelength, and propagation speed

Question 49

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

Answer 49

power

Question 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.

Answer 50

20% higher

Question 51

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

Answer 51

stiffness

Question 52

The unit for impedance is:

Answer 52

rayls

Question 53

In oblique incidence the incidence and reflection angles are always:

Answer 53

equal

Question 54

If frequency increases, period will _____.

Answer 54

decrease

Question 55

Stiffer media have higher or lower sound speeds?

Answer 55

higher

Question 56

Intensity is equal to the power of:

Answer 56

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

Question 57

20 kHz is equal to...

Answer 57

20,000 Hz.

Question 58

500 Hz is equal to...

Answer 58

0.500 kHz.

Question 59

TRUE OR FALSE Stiffer media have higher sound speeds.

Answer 59

TRUE

Question 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.

Answer 60

TRUE

Question 61

Attenuation encompasses:

Answer 61

- absorption. - scattering. - reflection.

Question 62

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

Answer 62

FALSE

Question 63

Impedance increases when ____ increases.

Answer 63

Density and propagation speed

Question 64

Pulse duration will not increase with...

Answer 64

frequency