DMS 120 - PHYSICS MIDTERM Flashcards
Interfaces that scatter ultrasound energy are usually considered to be…
those that are equal to or smaller than the wavelength.
Regions of lower pressure and density are called…
RAREFACTIONS
If you switch to a lower frequency for penetration, the wavelength of the transducer will…
increase
The attenuation of a 5.0-MHz transducer at a depth of 4 cm is ____ dB.
10.0 dB
The higher the transducer frequency, the higher the…
Rayleigh Scattering
The following are all ultrasound frequencies except:
15.0 kHz
The duty factor will increase with all of the following :
- pulse repetition frequency.
- pulse duration.
- period.
The attenuation of a 5-MHz transducer in soft tissue would be…
5.0 dB at 2 cm of depth
What is the period of a 5.0-MHz transducer in soft tissue?
0.2 µs
Impedance is equal to density multiplied by:
propagation speed
Continuous wave Doppler has a duty factor of ____ %.
100
For perpendicular incidence, the incidence angle is ___ degrees.
90
Attenuation decreases with an increase in:
wavelength
The average propagation speed in human soft tissue is ____.
1.54 mm/µs
Frequency is _____ proportional to wavelength.
inversely
The distance to a reflector in soft tissue is 15 cm. What is the round-trip time to this depth?
195.0 µs
Period is the ____ it takes for one ____ to occur.
time; cycle
In oblique incidence the sound is refracted at a boundary between ____ where propagation speeds are different.
two media
The propagation speed in soft tissue is not:
1.54 m/s.
____ 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
The pulse repetition frequency is the number of pulses that occur in a ____.
second
When frequency increases, the period…
decreases.
Amplitude is the maximum variation that occurs in an acoustic ____.
variable
3 dB of attenuation means?
One half the original intensity.
If beam power increases, intensity will…
increase
Propagation speed is the speed at which a wave:
travels through a medium.
Sound is a ____ longitudinal wave.
mechanical
The wavelength of 3-MHz ultrasound in soft tissue is ____
0.51 mm
CW sound is NOT described by:
pulse duration
____ is the number of complete cycles per second.
Frequency
As sound travels, the reduction in amplitude and intensity of the wave is called:
attenuation
Propagation speed is higher or lower in bone than soft tissue?
Higher
Sound requires a ___ through which to travel.
medium
Ultrasound pulses contain a range of frequencies called the ____.
bandwidth
Duty factor is:
unitless.
The spatial pulse length will not increase with:
frequency
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
Cycle, period, and frequency are examples of acoustic ____
parameters.
The fraction of time that pulsed ultrasound is on is called ____.
duty factor
Pulse repetition frequency is the ____ of pulses occurring in 1 second.
number
Attenuation is higher OR lower in bone than in soft tissue?
higher
Compression is not an _____.
acoustic variables
The best way to describe the role of ultrasound scattering in diagnostic imaging is:
that it allows us to see the tissue interfaces .
The distance to the reflector in soft tissue with a round-trip time of 39 µs is:
30 mm or 3 cm.
If the beam area decreases, the intensity will____.
increase
The four intensity values from the greatest to the least are:
SPTP, SATP, SPTA, SATA.
Heat production depends most directly on the ____ intensities.
SPTA
Pulsed wave ultrasound is not described by the terms such as:
frequency, wavelength, and propagation speed
The rate at which energy passes through a unit area is called _____.
power
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
Propagation speed is primarily determined by the ____ of the medium.
stiffness
The unit for impedance is:
rayls
In oblique incidence the incidence and reflection angles are always:
equal
If frequency increases, period will _____.
decrease
Stiffer media have higher or lower sound speeds?
higher
Intensity is equal to the power of:
a wave divided by the area over which the power is spread.
20 kHz is equal to…
20,000 Hz.
500 Hz is equal to…
0.500 kHz.
TRUE OR FALSE
Stiffer media have higher sound speeds.
TRUE
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
Attenuation encompasses:
- absorption.
- scattering.
- reflection.
TRUE OR FALSE
Spatial pulse length is determined by the length of the pulse and the propagation speed.
FALSE
Impedance increases when ____ increases.
Density and propagation speed
Pulse duration will not increase with…
frequency
