Physics Final Flashcards
T/F Macro means bigger and micro means smaller
True
T/F The symbol for millions is mega and millionths is micro
True
T/F The symbol for hundreds is giga and the symbol for hundredths is hecto
False; hundreds is hecto (h), hundredths is centi (c)
T/F A wave with a frequency of 15,000 MHz is ultrasonic
True
T/F If the power of a wave is halved, the intensity is reduced to one-fourth its original value
False; intensity is the power of a beam divided by its cross-sectional area. If we halve the power, we will halve the intensity
T/F If the amplitude of a wave is increased to 3 times its original value, the intensity is increased by 6 times
False; Intensity is proportional to the amplitude squared. If we triple the amplitude, we increase the intensity by a factor of nine.
T/F Propagation speed is determined by the medium
True
T/F Propagation speed increases as frequency increases
False; they are unrelated
T/F We need one intensity to calculate decibels
False; we need two intensities to calculate decibels
T/F As the path length increases, attenuation of US in soft tissue increases
True
T/F Spatial peak intensity is always lower than the spatial average intensity
False; Spatial peak intensity is always higher than the spatial average intensity
T/F In addition to location within the beam, sound wave intensities also vary over time
True
T/F SPTA intensity is the most relevant intensity with respect to tissue heating
True
T/F The duty factor is a unit less number with a value between 0 and 1
True
T/F There are two different methods to measure and report intensities
False; there are 6 different methods to measure and report intensities
T/F The duty factor for a pulsed ultrasound system is 2%.
False; with anatomic imaging the duty factor is 0.2%
T/F An ultrasound beam has the same intensity at different depths or at different side to side locations within the beam
False; the beam will have different intensities
T/F At a particular depth, the center of a sound beam is more intense than the edges
True
T/F Temporal peak intensity is maximum in time
True
How many hertz is 3MHz?
3,000,000 Hz
How much bigger is a billion than a million?
1,000
What are the units of wavelength?
unit of length, mm or m
What are the units of frequency?
Hertz; Hz
What are the units of intensity?
W/cm^2
What are the units of propagation speed?
units: m/s, mm/ μs, or any distance divided by time
What are the units of period?
units of time, microseconds, seconds, hours, or days
Of the following which grouping is determined by the sound source?
Amplitude, power, intensity
Period, frequency
If the intensity remains the same while the power is doubled, what happens to the beam area?
Doubles
A sound beam travels a total of 10cm in 2 seconds. What is the speed of the sound in this medium?
5cm/sec
What term describes the time from the start of a pulse to the end of that pulse?
Pulse duration
Pulse Repetition frequency is the reciprocal of..
Pulse Repetition Period
db is a mathematical representation with a __scale?
Logarithms
Rayleigh scattering is related to?
Frequency raised to the fourth power
Which of these media have the greatest attenuation and the slowest speed?
Bone
Which of the following mathematically describes the physics of refraction?
Snell’s Law
Two piezoelectric crystals are made from the same material. The thicker crystal will make a pulsed transducer with ______?
Lower frequency
Characteristics of an imaging transducer
- Pulses with short duration and length
- Uses backing material to limit ringing
- Reduced sensitivity
- Wide bandwidth or broadband
- Lower Q-factor
- Improved axial resolution
When PZT’s temperature exceeds the Curie point, the PZT is _______?
Depolarized
PZT in an ultrasound transducer is also known as
Ceramic, active element, or crystal
Which of the following describes the transducer component that reduces the “ringing” of the pulse?
Damping element or backing material
Mathematically, the Q factor is the main frequency divided by _____?
Bandwidth
Imaging transducers can also be referred to as ______?
Pulsed wave transducers
Which of the following crystals will produce sound with the lowest frequency?
- Thicker PZT crystal
- PZT with lower speeds
The damping material in the transducer improves the system’s _____ resolution?
Axial
If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is ____MHz.
With pulsed wave transducers, the frequency of sound is not determined by the electrical signal.
The impedance of a transducer active element is 1,900,000 Rayls, and the impedance of the skin is 1,400,000 Rayls. What is an acceptable impedance of the matching layer?
1,726,000 Rayls
*The impedance of the matching layer is between that of the active element and the skin
Of the following, which transducer component is a thin barrier of cork or rubber that isolates or “uncouples” the internal components of the transducer from the case?
Acoustic insulator
In an imaging transducer, what is the purpose of attaching the backing material to the PZT?
Reduces the ringing of the PZT
Which of the following probes creates a beam with the deepest focus?
- Higher frequency
- Larger diameter
Which of the following probes creates a beam with more divergence?
- Lower frequency
- Smaller diameter
Which of the following determines the frequency of sound created by a pulsed wave transducer?
- Speed of sound in the PZT
- Thickness of the PZT
Which of the following determine the spread of a sound beam in the far field?
- Transducer diameter
- Frequency of the sound
Of the following which term does not belong with the others?
Focus, end of the near zone, end of the Fraunhofer zone, middler of the focal zone
The end of the Fraunhofer zone is the very end of the sound beam
The frequency of a transducer does not change. If the diameter of the new piezoelectric increases, what happens to the wavelength?
No change
Imaging to a greater depth of view requires _____ listening?
Longer
When reporting a beam’s intensity at the location where it is maximum is referred to as?
Spatial peak intensity
The highest temporal intensity is which of the following?
Temporal peak
Choose the units for reporting intensity from the following
W/cm^2
Rank of intensities from largest to smallest
SPTP-Im-SPPA-SPTA-SATA
Which of the following is measured where intensity is maximum and averaged over all time?
SPTA
Which intensity is measured over the entire cross-sectional area of the sound beam, and over all time?
SATA
Synonyms for normal incidence
- Perpendicular
- Orthogonal
- Right angle
- 90 degrees
The intensity of the sound wave at the instant prior to striking a boundary is referred to as?
Incident intensity
The portion of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling is referred to as the?
Transmitted intensity
The percentage of the US intensity that is allowed to pass through when the beam reaches a boundary between two media is referred to as?
Intensity transmission coefficient (ITC),
A sound wave with an intensity of 50W/cm2 strikes a boundary and is totally reflected. What is the intensity reflection coefficient?
100%
The intensity reflection coefficient of sound is 99.9%. What percent of sound is transmitted into the body?
0.1%
Specular reflections arise when the interface is ______?
Smooth
What do we know about oblique incidence?
Nothing!
Transmission with a bend is referred to as?
Refraction
Snell’s law describes what physics?
Refraction
Sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?
Refraction will not occur when the speeds of the two media are identical
What processes occur as the ultrasound passes through all media?
- Reflection
- Scattering
- Absorption
Two waves are traveling through a medium and arrive at a location at the same time. What event takes place?
Interference
The percentage of time that a system is transmitting a pulse refers to which of the following?
Duty factor
A 3MHz sound beam travels through two media. It attenuates 5 dB in medium A and 6 dB in medium B. What is the total attenuation that the sound beam undergoes as it travels through both media?
11 dB
* 5dB+6dB=11dB
Which of these are considered the dominant contributor to attenuation?
Absorption
Hertz is a unit of measurement used to describe what wave characteristic?
Frequency
A low frequency transducer is best at imaging which anatomical structure?
OB/AB
Which of the following is the best estimate for attenuation coefficient of sound traveling in soft tissue?
Is the one-half the frequency
Atten. coef. = 0.5 dB/cm/MHz
Attenuation is determined by two factors
- Path length
- Frequency of sound
With longer distances and higher frequencies you have?
More attenuation
With shorter distances and lower frequencies you have?
Less attenuation
Because attenuation means a weakening or a decrease, the dbs must be?
Negative
Which term best describes redirection of sound in many directions?
Scattering
Reflections from a smooth reflector are referred to as?
Specular Reflection
When a boundary is rough, reflected sound is disorganized and random, also called?
Diffuse reflection, or backscatter
Rayleigh scattering increases dramatically with increasing frequency, which is the relation?
Its proportional
Acoustic Impedance is equal to?
Density (kg/m^3) * prop. speed (m/s)
A sound wave is created by the transducer, reflects off of an object and returns to the transducer. The depth of the reflector is 10 cm. The round trip time is 2 seconds. What is the speed of sound in the medium?
10 cm/sec
*10cm + 10 cm= 20cm
20cm/2 sec=10 cm/sec
The time needed for a pulse to travel to and from the transducer and the reflector is called?
Time-of-flight
A sound wave is created by the transducer, reflects off an object and returns to the transducer in 52 microseconds. How deep is the object and what is the total distance traveled?
4cm, 8 cm
The maximum imaging depth during an ultrasound exam is 5 cm. The sonographer adjusts the depth to 10cm. What happens to pulse repetition frequency?
It will 1/2. PRF is inversely related to the maximum imaging depth
The maximum imaging depth during an ultrasound exam is 4cm. The sonographer adjusts the imaging depth to 8 cm. What happens to the pulse repetition period?
It will double. PRP is directly related to the maximum imaging depth
A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The time of flight is 130 microseconds. What is the maximum PRF?
7,700 Hz
*PRF(Hz) = 77,000 cm/s / 10cm
A sound wave is created by the transducer, reflects off an object, and returns to the transducer. The go return time is 39 microseconds. What is the total distance traveled?
6 cm
Axial resolution deals with structures that are ______ to the sound beam.
Front-to-back, or parallel
As frequency increases, the numerical value of LARRD resolution _______?
Decrease
Which of the following has the highest axial resolution?
- Less ringing
- Higher frequency
Superior axial resolution is associated with the following?
- Shorter spatial pulse length
- Shorter pulse duration
- Higher frequencies (short wavelengths)
- Fewer cycles per pulse (less ringing)
- Lower numerical values
Two different transducers create pulses. Both transducers create sound with a frequency of 5MHZ. Which of the following is more likely to create a better image in regards to axial resolution?
The one with fewer cycles per pulse and shorter pulses
Which of the following transducers will create the lowest numerical value of axial resolution?
Highest frequency
Effects of focusing
- Beam diameter in near field and focal zone is reduced
- Focal depth is shallower
- Beam diameter in the far zone increases
- Focal Zone is smaller
Display modes
A-mode –Amplitude
B-mode –Brightness
M-mode –Motion
What is the only display mode that provides information regarding reflector motion with respect to time?
M-mode
What display mode looks like a big city skyline?
A-mode
What display mode was the first form of gray scale imaging?
B-mode
A-mode display axes
X-axis: depth of the reflector
Y-axis: amplitude of the reflected signal
With M-mode, what is displayed on the x-axis?
Time
With B-mode, what is displayed on the y-axis?
Nothing! -trick question
Depth is displayed on what axis of M-mode?
Y-axis
Which display mode uses the z-axis?
B-mode; Amplitude
With B-mode, what is displayed on the x-axis?
Depth of the reflector
Acoustic propagation properties
The effects of the medium upon the sound wave
Biologic effects
The effects of the sound wave upon the biologic tissue through which it passes
Sound must travel through a medium, where molecules are alternately _____ and _____
Compressed and rarefied
Acoustic variables of a sound wave
- Pressure
- Density
- Distance
Acoustic parameters of a sound wave
- Period
- Frequency
- Amplitude
- Power
- Intensity
- Wavelength
- Propagation speed
Stiffness
The ability of an object to resist compression
Density
The relative weight of a material
Materials that are stiff but not dense will have the..
Fastest speed
Materials that are not stiff and very dense will have the..
Slowest speed
Five parameters that describe pulsed sound
- Pulse duration
- Pulse repetition period
- Pulse repetition frequency
- Duty factor
- Spatial pulse length
Shallow imaging
- Less listening
- Shorter PRP
- Higher PRF
- Higher duty factor
Deep imaging
- More listening
- Longer PRP
- Lower PRF
- Lower duty factor
Five words that are related to the intensities of pulsed waves
- Spatial
- Peak
- Average
- Temporal
- Pulsed
3 dB means..
Double
10 dB means..
ten times larger
-3 dB means..
half
-10 dB means..
one-tenth
T/F A tissue’s impedance is calculated, not measured
True
What two physical principles always apply to reflection with oblique incidence?
- Conservation of energy
- Reflection angle=incident angle
Refraction occurs only if conditions are satisfied:
- Oblique incidence
- Different propagation speeds of the two media
Which of these media have the greatest attenuation and the fastest speed?
Bone
