Davies Quizlet Starred Flashcards
A hydrophone measures (2)
Duty factor
Pressure amplitude
PHI stands for
Protected health information
What does mechanical index indicate on ultrasound system
Liklihood of cavitation during an US exam
Potential bio effect occuring through absorption of sound energy by tissue
Heating
You notice TI is greater than 1. Any increase in temp would most likely be greatest in
Bone
Motion of particles in a fluid is sometimes observed in an intense US beam. This is termed
Acoustic streaming
TI reading is 1. What does this indicate?
The output level is high enough that temperature could increase as much as 1 C if the transducer were held stationary
When scanning with pulsed-wave dop, you would affect the acoustic exposure by changing which of the following?
PRF
Tissue with the highest rate of attenuation
Lung
Propagation speed is lowest in which tissue
Fat
Purpose of gel coupling medium
Decrease impedance mismatch
Sound does not travel through air
While imaging a cyst, you notice shadowing posterior to each lateral border of the cyst. What is the source of the shadows?
Bending of the sound beam due to different media propagation speeds
Diffraction
Pattern produced by a sound beam after passing through a small aperture
Sound propagates faster in materials with greater
Stiffness
During an US, you would most likely encounter refraction in this fiew
Curved interface
Relationship to frequency and absorption
If frequency is doubled, absorption is doubled
While performing a sonogram, you encounter the following interfaces*** which will produce the weakest REFLECTED signal
Organ parenchyma/organ parenchyma
You are scanning a large mass that is composed primarily of fat. What is most likely to happen?
Axial misrepretation of objects distal to the mass on the screen due to the slower propagation speed through fat
When you change the transmit frequency, what is altered?
Number of cycles per second
When the sound beam is refracted, what may you detect on the ultrasound image?
lateral misregistration
What interaction of ultrasound and tissue is primarily responsible for imaging the internal structure of organs?
scattering
when you image a specular reflector, the strength of the recieved signal depends on (2)
- angle of incidence
- difference in acoustic impedance
T/F frequency, intensity, amplitude and wavelength change as the beam propagates through tissue
true
axial resolution is determined chiefly by
pulse duration
benefits of harmonic imaging (2)
- improve lateral resolution
- decrease grating lobes
what increases SPL?
n = number of cycles per pulse
increased bandwith improves what type of resolution
axial
For a linear array transducer consisting of a single row of elements, what method is most used to focus the beam in the elevational direction?
mechanical focusing
downfall to small footprint transducer
degrades resolution
sector display format that narrows to a point at the transducer surface. what transducer?
phased array
type of transduer that has the same measurement for elevational and lateral resolution
annular array
During the course of a sonographic exam, you notice lateral splaying of the echoes in the far field. What can you do to improve the image?
Increase the number of transmit focal zones and optimizes their location
You suspect that a bright spot on the B-mode image is a calcification, but a posterior acoustic shadow is not present. How can you best optimize your system to demonstrate a shadow distal to the calcification
Increase the transducer frequency
What is the purpose of the radiofrequency shield that is placed around the crystal and backing material of the ultrasound probe?
It reduces electromagnetic interference
What is the optimal thickness for the matching layer?
One-fourth of a wavelength
Parallel processing, define
A method used to improve frame rates with multizone electronic focusing is termed:
Which of the following best describes the f-number?
Focal length divided by the aperture
If you wish to perform a sonogram with the largest possible field of view in both the near field and at depth, what type of array transducer would be most preferable?
Curved array
how many cycles in a pulse with B-mode
1-3
What is purpose of applying multiple matching layers to the transducer face? (2)
- decreases impedance
- increased bandwidth
What is the main advantage the stand-off pad provides to improve the image?
The stand-off pad increases the distance between the transducer and the mass, making it more likely that the mass will be located close to the elevational focus of
If you are using a transducer with poor elevation resolution, which of the following problems are you most likely to encounter?
Inability to clearly demonstrate small cystic structures
What can you do to improve contrast resolution in the ultrasound image?
Use a 2D or matrix array transducer
Which represents the best measure of resolution for modern day ultrasound scanners?
Axial
Which of the following transducer types is best suited to cardiac imaging?
Phased array
tissue equivalent phantom measures (4)
- axial resolution
- contrast resolutino
- lateral resolution
- slice thickness
You notice a loss of detail in the lateral dimension of the ultrasound image. What can you do to improve this?
increase scan line density
What is the purpose of curving the transducer elements or applying a lens over the elements?
To provide focusing in the out-of-plane (elevational) direction
What disadvantage and advantage is related to the use of a tightly curved array transducer?
advantage: field of view is improved
disadvantage: Lateral resolution degrades with depth
In order to focus a sound beam relatively far away from the transducer, it is advantageous to:
Increase the diameter of the element
increasing frame averaging aka persistence does what to frame rate
decreases
The technique of frame averaging during real-time acquisition is designed to
Reduce random noise
You are performing a sonographic examination and select the tissue harmonics operating mode. What advantage will you obtain over conventional imaging?
Improved contrast resolution
What is a typical frame rate for B/mode real-time imaging?
10-50 Hz
The term duty factor is defined as
The fraction of time the transducer is actively transmitting sound
If you increase the pulse repetition frequency and leave all other controls unchanged, what will happen?
frame rate decreases
What effect will you see in image if you increase the reject level?
Decreased low-level echoes
If sound did not attenuate with increasing depth, what system control would you no longer need?
reject
What system component determines the repetition frequency?
pulser
What is the purpose of the preamplification of the incoming signal that occurs in the transducer assembly?
To increase echo voltages before noise is induced through the cable
What function of the receiver converts electrical signals from radiofrequency to video form?
demodulation
Which of the following best describes M-mode?
Depth of reflectors along a single line of sight vs time
What information is present in the M-mode display? (3)
time, motion pattern, amplitude
A digital scan converter is another name for what system component?
image memory
Where are images stored in the ultrasound system?
scan converter
The picture elements in a scan converter matrix are termed
pixels
Digital to analog conversion of the ultrasound signal must occur at what part of the imaging process?
between the scan converter and the display
when you “freeze’ the image, where is the echo information stored?
scan converter
What is the order in which the signal travels in the ultrasound system?
Transducer, receiver, scan converter, display
Of the following, which is the best choice to help you demonstrate tissue boundaries that are not perpendicular to the sound beam?
spatial compounding
benefits of 3D imaging over 2D (2)
- ability to display image planes impossible to obtain with 2D imaging
- Ability to display orthogonal planes simultaneously
You may observe a mirror image artifact with which imaging mode?
ALL OF THEM - b-mode, spectral, colour, power
Which imaging technique may increase visualization of the reflections from blood flow on the real-time ultrasound image?
harmonics
Which of the following artifacts commonly results in echoes filling in the lumen of small vessels?
partial volume
Propagation speed error results in which sonographic appearance?
Improper axial position of an echo
When you select harmonic imaging, which artifact is less likely to be observed?
Grating lobes
When you select compound imaging, which artifact is less likely to be observed? (4)
- refraction
- -shadowing
- enhancement
- speckle
what will decrease acoustic speckle in your image (2)
- frame averaging
- compound
If you wish to improve border definition, what imaging enhancement should you use?
spatial compounding
What can you do to improve visualization of distal acoustic shadowing from calcification?
harmonics
What helps to improve the axial resolution in a B-mode image?
increased bandwidth
what helps to improve the lateral resolution in a B-mode image?
increased aperture
what helps to improve the elevation resolution in a B-mode image?
Focusing with an acoustic lens
What technique would be most likely to produce grating lobes in your image?
beam steering
What term is used to describe a 3-dimensional pixel element in 3D sonography?
voxel
What 2D limitation is addressed by 3D ultrasound imaging?
3D provides visibility of the coronal plane
The packet size in color Doppler refers to the number of
Pulse/listen cycles per acoustic scan line
A commonly used process for determining direction in a Doppler instrument is
Phase quadrature detection
What method is used to steer the color beam with a linear array transducer?
What method is used to steer the color beam with a linear array transducer?
What would be the most likely result from increasing the transmit frequency of the color Doppler?
Improved sensitivity to slow flow
During Doppler interrogation of the carotid artery, you detect mirroring. Which of the following is a common cause of this artifact?
Doppler angle of interrogation near 90
The rapid technique used in most color Doppler systems to obtain the mean doppler frequency shift is:
Autocorrelation
packet size
number of pulses per scan line
Color flash artifact obscuring the anatomy of interest in an exam of the abdominal aorta. What can you do to reduce impact of the flash?
Increase the wall filter
You have increased the packet size while using color Doppler to evaluate flow. What position result will occur from this action?
Improved signal-to-noise ratio
What two controls affect the spatial resolution of the color image?
frequency and line density
Which condition is most likely to occur in patients having a normal arterial waveform shape, but low velocities across all vessels?
Low cardiac output
Atherosclerosis begins within:
the intima
String test objects are used to evaluate:
Doppler accuracy
recommended ingredient in cleansers for intracavitary probes?
Glutaraldehyde
You are using a transducer with poor elevation resolution. What problem will most likely be encountered as a result?
You will not be able to clear anechoic tubes oriented with their axis in the scan plane
When measuring penetration on a tissue-mimicking phantom, how should the master gain and acoustic output be adjusted?
Maximum gain, maximum acoustic output
