Final Review Flashcards
Snell’s law describes physics of
refraction
Name the three components of attenuation
Scattering, Absorption, reflection
If the power is unchanged and the beam area doubles, what happens to the intensity?
it halves
If intensity goes up by 25%, what happens to power?
it goes up 25%
Reflection requires the media to have different
Impedance
Wavelength has the greatest effect on
Axial resolution
If the PRF increases, the duty factor
increases
Longitudinal waves are parallel to the axis of the wave propagation where as transverse waves are perpendicular to the wave propagation. T or F
True
Spatial pulse length _______ if the frequency is increased.
Decreases
Propagation speed describes the number of waves in the medium.
T or F
False
Initially, what determines the amplitude of an ultrasound wave?
Ultrasound System
The maximum variation of an acoustic variable from its baseline is
Amplitude
A reduction in intensity of a sound beam to one half its original intensity is a _____ db change
-3
db is a mathematical representation with a _____ and _____ scale
Logarithmic and relative
Name the units of attenuation
decibels or dB
a sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?
0%
As an ultrasound wave travels through the body, its amplitude usually;
Decreases
The power of an ultrasound wave can be reported with which of the following?
Watts
When a sonographer decreases the amplitude of a wave to 1/2 of its original value, how has the power changed?
Decreases 25%
The intensity of an ultrasound beam is defined as the ____ in the beam ____ by the _____ of the beam
Power, divided, cross sectional area
What is impedance?
The resistance of a medium to the sound traveling through it
Reflection requires the media to have different
Impedance
The two things that are required for refraction to occur are:
Oblique incidence, media with different sound speeds
With specular reflection, the strength of the received signal depends on the following two factors?
Difference in acoustic impedance, angle of incidence
For soft tissue, one of the factors responsible for determining acoustic impedance is
Density
What interaction of ultrasound and tissue is primarily responsible for imaging the internal structure of organs?
Scattering
What sound tissue interaction is necessary to form an ultrasound image?
Reflection
Which of the following describes diffuse reflection?
The reflected beam is scattered in various directions
If you choose a lower frequency transducer to image a highly attenuating liver, what tradeoff are you making?
Decreased spatial resolution
Decreasing the following parameter will improve axial resolution
Spatial pulse length
Concentration of force or pound per square inch or pascal’s?
Pressure
Concentration of mass or mass per unit volume
Density
The speed of sound is fastest in solids
T or F
True
Wavelength always _____ as frequencies increase.
Decrease
Perpendicular incidence is also known as normal incidence.
T or F
True
Refraction requires the 2 media to have different _______.
Propagation speeds
Which of the following will increase the duty factor?
Increasing PRF
The amplitude of an echo from a specular reflector depends on all of the following EXCEPT?
angle, attenuation, PRF, distance
PRF
What is the approximate coefficient for 1 MHz US in soft tissue?
.5 db/cm
You are scanning the liver at an incidence angle of 45 degrees. When the sound hits the interface of a hemangioma and reflects off it, the reflection angle will be______.
45 degrees
Pulse repetition frequency is directly related to pulse repetition period.
T or F
False
The spatial pulse length
Determines axial resolution
An ultrasound wave is a mechanical longitudinal wave.
T or F
True
Compressions are regions of higher pressure. Rarefactions are regions of lower pressure in a sound wave.
T or F
True
Constructive interference in a sound wave are also called out-of-phase waves.
T or F
False
Destructive interference is also called out-of-phase waves.
T or F
True
By adjusting the imaging depth, the sonographer can change the pulse repetition period, pulse repetition frequency, and the duty factor.
T or F
True
Wavelength has the greatest effect on axial resolution.
T or F
True
Beam uniformity is a unitless ratio that describes the distribution of an ultrasound beam in space.
T or F
True
Temporal peak and temporal average intensities are the same for pulsed ultrasound
T or F
False
A wave’s intensity is 2mW/cm2. There is a change of +9 dB. What is the final intensity?
16mW/cm2
The sonographer does not have the ability to change the power and intensity of the machine.
T or F
False
The formula for power is
Power = Intensity x Cross section (beam area)
If the power is unchanged and the beam area doubles, what happens to intensity?
It halves
3 dB change means the intensity will double in value.
T or F
True
Attenuation decreases when frequency increases or path length increases.
T or F
False
What is the actual time that an US machine is creating a pulse?
Pulse duration
If the amplitude of a wave is increased to 3 times its original value, what happens to the intensity?
Intensity increases 9 times
A linear phased array has a/an _____ footprint?
Small
All of the following are TRUE about bandwidth EXCEPT:
Longer pulses have narrower bandwidths and provide better resolution
Preprocessing functions can be defined as:
A function that is performed before the echo data are stored in scan converter memory
The spatial pulse length
Determines axial resolution
To generate an ultrasound image, what is the order of activation for these system components?
P - T - R- M- VD
Pulser, Transducer, receiver, memory, video display
Demodulation and rejection are functions of the
Receiver
An annular array uses _____ beam steering
Mechanical
Spatial pulse length can be improved by
using greatly damped transducers
At one near zone length the beam is
Half the transducer diameter
The piezoelectric effect, heat energy is converted to mechanical energy.
T or F
False
Mechanical to electric
Focal depth is indirectly related to crystal diameter and frequency of US in the crystals
T or F
False
Point at which a man made transducer becomes deplarized
Curie point
Frequency is inversely related to the speed of sound in the crystals.
T or F
False
Which of the following will NOT result in a shorter pulse duration?
Using a lower propagation velocity
One way the sonographer can change the axial resolution is by adjusting the maximum imaging depth.
T or F
False
With this transducer, a defective crystal will cause a horizontal line dropout across the image.
Annular array
Which of the following lists is correct for the impedance from highest to lowest
PZT, matching layer, gel, skin
The best lateral resolution can be realized at
The focus
The range of frequencies within a pulse
Bandwidth
how does bandwidth relate to pulse duration and SPL
SPL and pulse duration = directly related
BOTH inversely related to bandwidth
A transducer with a wide bandwidth is likely to have
Good axial resolution
Which of the following transducers has the best lateral resolution in far zone
Highest frequency, largest crystal diameter
an annular array uses _____ beam steerer
Mechanical
Spatial pulse length can be improved by
using greatly damped transducers
with these transducers a defected crystal will cause a vertical line dropout in the image.
Linear switched array, convex sequential
A curved electrical spike firing pattern yields a?
Focused beam
We adjust the “receiving focus” or “dynamic aperture” when we adjust the focal zones on the machine.
T or F
False
Which of the following determines the frequency in a pulse wave transducer
thickness and propagation speed
States that the wavelength energies combine together to transmit energies along a central axis to give a beam shape of an hour glass.
Huygens
Which of the following has the deepest focus
6 MHz, 6mm crystal diameter
The beam of an unfocused transducer diverges
Fraunhofer zone
Frequency is inversely related to crystal thickness
T or F
True
At 2 near zone length, beam diameter is twice the transducer diameter.
T or F
False
With these transducers, a defected crystal will cause poor steering and focusing in the image
Linear phased array, convex phased
A defective crystal in this transducer will cause the entire image to be lost
Mechanical transducer
Which of the following determines the frequency in a continuous wave transducer
electrical signal from the voltage applied to the PZT
Doubling the frequency causes axial resolution to be doubled.
T or F
False
Doubling the aperture increases the near zone length.
T or F
True
Axial resolution is
The ability to distinguish two objects parallel to the ultrasound beam
Electronic focusing in slice thickness requires 1-2 rows of elements.
T or F
False
Which of the following transducers can be electronically steered
sector phased array and linear phased array
Axial resolution equals the spatial pulse length divided by 2.
T or F
True
Reduces the reflection at the transducer-tissue interphase
Matching layer
You decide to narrow your sector size from 90 to 45 degrees. The frame rate is
Doubled
All of the following decrease/degrade temporal resolution except…
Narrower sector
Which of the following will decrease temporal resolution
Increasing the number of scan lines
You decide you need to increase the line density by 4 times to improve your resolution, what also happens
The temporal resolution decreases
When you increase scanning depth, which one of these automatically decreases by the system to avoid range ambiguity
PRF
You finish your longitudinal kidney image and turn transverse. you decide to narrow your sector size to half the original. If the frame rate remains unchanged, which of the following must happen
the line density was doubled
Which of the following will increase duty factor, thereby improving temporal resolution
Increasing the PRF
Which of the following is consistent with improved temporal resolution
Higher frame rate
The number of images displayed per second in real time imaging is called
Frame rate
You decide to change from 5 focal zones to 1 focal zone what is the result
The temporal resolution increases
What is the primary advantage of multiple focal zones along each scan line in 2D images
improved lateral resolution
Frame rate is limited by the speed of sound in a medium and/or the depth of the view.
T or F
True
For each focus on a scan line in each frame a ______ is required
pulse
Which of the following will decrease temporal resolution
Increasing the number of scan lines
The fraction of the time the sound is transmitting is the
Duty Factor
An ultrasound system with shorter pulse duration will generally have better temporal resolution.
T or F
False
When penetration is multiplied by the number of foci, the number of scan lines per frame and the frame rate, the result cannot exceed
77,000
which of the following does not decrease the frame rate
Increasing the receiver gain
If the number of foci increases, the frame rate increases.
T or F
False
In a real time scanner, which of the following choices determines the maximum frame rate.
Depth of View
Which of the following exams would require the best temporal resolution
Cardiac
Imaging deeper into a structure gives better temporal resolution.
T or F
False
The production of deformation from voltage is called
Piezoelectric effect
Preprocessing functions may be defined as
A function that is performed before the echo data are stored in memory
Use the minimum output power and the highest receiver gain required to produce optimal images describes which principle?
ALARA
The master synchronizer functions to
Communicate with all the individual components of the US system
Organize and times their function
Prepares them to operate as a single integrated system
What control could you adjust the signal to noise ratio
Power
Creates an image of uniform brightness from top to bottom
Compensation
Changes the signal form to one more suitable for TV display
Demodulation
Every signal is treated identically
Amplification
Affects all low level signals everywhere on the image
Rejection
Decreases the dynamic range
Compression
A-mode scanning represents the depth of the signal in the horizontal dimension.
T or F
True
An ultrasound wave is a mechanical longitudinal wave.
T or F
True
The depth of a reflector is 2cm deep. what is the time of flight?
26us
The pulse generates the voltages that drive the transducer.
T or F
True
In which case is the temporal resolution least important important
Thyroid
While scanning an obese patient for an abdomen, you increase both imaging depth and the scan line density, what also happens
Reduced temporal resolution
Increasing the transducer frequency will also have an effect on temporal resolution.
T or F
False
A sonographer using a phased array US machine turns off multi-focus feature, what is most likely the consequence of this action
the temporal resolution improves
Which operator control allows you to alter frame rate?
Depth
You need better spatial resolution to improve your image, which of the following adjustments will improve spatial resolution?
Increasing the frequency
Which of the following ultrasound imaging modalities has the poorest temporal resolution
Color flow imaging
PRF and frame rate are directly related.
T or F
True
You are scanning a patient and your frame rate is so slow, you decide to do something to increase it, what do you do to have a faster frame rate
Decrease the number of scan lines
If you are scanning a left lobe of the liver and are at 8cm depth, then scan the right lobe and switch to 16cm depth, what can you do to keep your frame rate the same.
Narrow your sector
If the image depth of a scan is 15cm and there are 100 lines in the image, the number of pulses making up the scan is 100.
T or F
True
A-mode scanning represents the depth of the signal in horizontal dimension.
T or F
True
The amplitude of the reflection represented on a B-mode image is on the ____ axis
Z axis
The elimination of voltages that do not exceed a certain level is
Rejection
If the reflector is sitting twice as far away from the transducer, what effect will this have on the time of flight of sound pulse?
Double it.
The x axis of M-mode measures what?
Time
Rectification is the process of turning positive voltage into negative voltage.
T or F
False
When only bright reflecting objects and nothing else is displayed on the ultrasound machine, the sonographer should.
Adjust the reject level
The scan converter is part of the ultrasound system that contains the memory bank.
T or F
True.
An ultrasound system is operating on the harmonics mode, the harmonic frequency is on 8MHz, what is the transmitted frequency?
4 MHz
The ultrasound machine transmits a pulse with a fundamental frequency of 4MHz. when the sonographer switches to harmonic mode, what will the harmonic frequency be?
8MHz
The distance to a reflector is doubled, the time of flight for the pulse to travel to the reflector and back is
2 times
The range equation represents the relationship of the distance of the reflector to ____ and _____
Time of flight, distance
