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Ultrasound Physics - Kremkau Chapter 2 review ques
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Flashcards
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End of chapter excercises
Terms in this set (95)
A wave is a traveling variation in quantities called wave ___________.
variables
Sound is a traveling variation in quantities called _________ variables.
acoustic
Ultrasound is sound with a frequency greater than _________Hz.
20,0000
Acoustic variables include:
pressure, density, and particle vibration
Frequency is the number of _________ an acoustic variable goes through in a second.
cycles
The unit of frequency is ____________, which is abbreviated _______.
hertz, Hz
Period is the __________ that it takes for one cycle to occur.
amplitude
Period decreases as __________ increases
frequency
Wavelength is the length of ________ over which one cycle occurs.
space
Propagation speed is the speed with which a _______ moves through a medium.
wave
Wavelength is equal to:
propogation speed divided by frequency.
The _______ and _________ of a medium determine propagation speed.
density and stiffness
Propagation speed increases if _________ is increased.
stiffness
The average propagation speed in soft tissues is __________m/s or __________mm/microsecond.
1540, 1.54
Propagation speed is determined by the:
medium
The wavelength of 7 -Mhz ultrasound in soft tissues is _________mm.
0.22
Wavelength in soft tissues _________ as frequency increases.
decreases.
It takes _________ microseconds for ultrasound to travel 1.54 cm in soft tissue.
10
Propagation speed in bone is __________ that in soft tissue.
higher than
Sound travels fastest in
steel
Solids have higher propagation speeds than liquids because they have greater ________.
stiffness
Sound travels slowest in
gases
Sound is a _________ _____________ wave.
mechanical longitudinal
If propagation speed is doubled (a different medium) and frequency is held constant, the wavelength is __________.
doubled
If frequency in soft tissue is doubled, propagation speed is _______.
unchanged (determined by the medium)
If wavelength is 2 mm and frequency is doubled, the wavelength becomes __________mm.
1
Waves can carry ___________ from one place to another.
information
From given values for propagation speed and frequency, what can be calculated?
wavelength
If two media have different stiffness, the one with the higher stiffness will have the higher propagation speed. True of False?
True
The second harmonic of 3 MHz is __________ MHz.
6
The odd harmonics of 2 MHz are _____ MHz.
6, 10, 14
The even harmonics of 2 MHz are _______ MHz.
4,8,12
Nonlinear propagation means that __________.
propagation speed depends on pressure, the waveform changes shape as it travels.
As a wave changes from sinusoidal form to sawtooth form, additional ___________ appear that are __________ and ________ multiples of the _________. They are called ____________.
Frequencies, even, odd, fundamental, harmonics.
If the density of a medium is 100o0kg/m3 and the propagation speed is 1540m/s, the impedance is _______ rayls.
1,540,000
If two media have the same propagation speed but different densities, the one with the higher density will have the higher impedance. TRUE or False?
True
If two media have the same density but different propagation speeds, the one with the higher propagation speed will have the higher impedance. TRUE or FALSE.
True
Impedance is __________ multiplied by __________ _____________.
Density, propogation speed
The abbreviation CW stands for _________.
Continuous wave
Pulse repetition frequency is the number of __________ occurring in 1 second.
Pulses
Pulse repetition _______ is the time from the beginning of one pulse to the beginning of the next.
Period
Pulse duration is the __________ it takes for a pulse to occur.
Time
Spatial pulse length is the __________ of ________ that a pulse occupies as it travels.
Length, space
_________ __________ is the fraction of time that pulsed ultrasound is actually on.
Duty factor
Pulse duration equals the number of cycles in the pulse multiplied by __________.
period
Spatial pulse length equals the number of cycles in the pulse multiplied by ________.
wavelengths
The duty factor of continuous wave sound is ___.
1 (100%)
If the wavelength is 2 mm, the spatial pulse length for a three-cycle pulse is ________mm.
6
The spatial pulse length in soft tissue for a two-cycle pulse of frequency 5 MHz is ______mm.
0.6 (soft tissue propagation speed is 1.54 mm/microsecond; wavelength is 0.3mm)
The pulse duration in soft tissue for a two-cycle pulse of frequency 5 MHz is ______ microseconds.
0.4 (Period is 0.2microseconds; soft tissue is irrelevant)
For a 1 - kHz pulse repetition frequency, the pulse repetition period is ____________ ms.
1 (1000 pulses per second; 1/1000 second from onepulse to the next)
How many cycles are there in 1 second of continuos wave 5-MHz ultrasound?
5,000,000
How many cycles are there in 1 second of pulsed 5-MHz ultrasound with a duty factor of 0.01 (1%)?
50,000
For pulsed ultrasound, the duty factor is always ____ _____ one.
less than
__________ is a typical duty factor for sonography?
0.1
Amplitude is the maximum _________ that occurs in an acoustic variable.
Variation
Intensity is the _________ in a wave divided by ________.
Power, area
The unit for intensity is ________.
W/cm3 or mW/cm2
Intensity is proportional to ________ squared.
Amplitude
If power is doubled and area remains unchanged, intensity is __________.
doubled
If area is doubled and power remains unchanged, intensity is ________.
halved
If both power and area are doubled, intensity is _________.
unchanged
If amplitude is doubled, intensity is _________.
quadrupled
If a sound beam has a power of 10 mW and a beam area of 2 cm2, the spatial average intensity is _________mW/cm2.
5
Attenuation s the reduction in ________ and ________ as a wave travels through a medium.
Amplitude, intensity
Attenuation consists of:
absorption, reflection, scattering
The attenuation coefficient is attenuation per ________ of sound travel.
centimeter
Attenuation and the attenuation coefficient are given in units of _____ and _________, respectively.
dB, dB/cm
For soft tissues, there is approximately _____dB of attenuation per centimeter for each megahertz of frequency.
0.5
For soft tissues, the attenuation coefficient at 3 MHz is approximately ___________.
1.5 dB/cm
The attenuation coefficient in soft tissue _________ as frequency increases.
increases
For soft tissue, if frequency is doubled, attenuation is __________. If path length is doubled, attenuation is _________. If both frequency and path length are doubled, attenuation is _____.
doubled, doubled, quadrupled
If frequency is doubled and pathe length is halved, attenuation is _______.
unchanged
Absorption is the conversion of ________ to _____.
Sound, heat
Can absorption be greater than attenuation in a given medium at a given frequency?
NO
Is attenuation in bone higher or lower than in soft tissue?
Higher
The imaging depth (penetration) _______ as frequency increases.
Decreases
If the intensity of 4-MHz ultrasound entering soft tissue is 2 W/cm2, the intensity at a depth of 4 cm is ________ W/cm2.
0.32 (Attenuation is 8 dB, and intensity ratio is 0.16)
If the intensity of 40-MHz ultrasound entering soft tissue is 2 W/cm2, the intensity at a depth of 4 cm is ________ W/cm2.
0.00000002 (Attenuation is 80 dB, and intensity ratio is 0.00000001)
The depth at which half-intensity occurs in soft tissues at 7.5 MHz is _________.
0.8 (0.5 x 7.5 MHz x 0.8 cm = 3 dB)
When ultrasound encounters a boundary with perpendicular incidence, the _________ of the tissues must be different to produce a reflection (echo).
Impedences
With perpendicular incidence, two media ______ and the incident _______ must be known to calculate the reflected intensity.
Impedences, intensity
With perpendicular incidence, two media _______ must be known to calculate the intensity reflection coefficient.
Impedances
For an incident intensity of 2 mW/cm2 and impedances of 49 and 51 rayls, the reflected intensity is ________ mW/cm2, and the transmitted inensity is _________ mW/cm2.
0.0008, 1.9992
If the impedances of the media are equal, there is no reflection. True or false?
True, for perpendicular incidence
With perpendicular incidence, the reflected intensity depends on the ________.
impedance difference and impedance sum (difference in numerator; sum in denominator)
Refraction is a change in __________ of sound when it crosses a boundary.
direction
Refraction is caused by a change in __________ __________ at the boundary
propagation speed
Under what two conditions does refration not occur?
perpendicular incidence & equal media propagation speeds
The low speed of sound in fat is a source of image degradation because of refration. If the incidence angle at a boundary between fat (1.45 mm/microsecond) and kidney (1.56) is 30 degrees, the transmission angle is ___________ degrees?
32
Redirection of sound in many directions as it encounters rough media junctions or particle suspensions (heterogenous media) is called ____.
Scattering
Backscatter helps make echo reception less dependent on incident angle. TRUE or FALSE?
True
What must be known to calculate the distance to a reflector?
travel time and speed
No reflection will occur with perpendicular incidence if the media _______ are equal.
Impedances
Scattering occurs at smooth boundaries and within homogenous media. TRUE or FALSE?
False
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