SPI Review Flashcards
The thickness of the matching layer is ________ the wavelength
1/4
What do the piezoelectric crystals do?
Convert electrical signals to acoustic pulses
The thickness of the PE is ________ the wavelength
1/2
What does frequency depend on in the transducer?
element thickness
Thicker element = _______ frequency
lower
Wider element diameter = ___________ beam intensity
low
Higher frequency = ___________ axial/lateral resolution and ________ penetration
improved / less
What does the damping/backing layer do?
reduces the ringing
Damping _________ axial resolution and decreases the ________
improves / SPL
What is the footprint?
The portion of the transducer that touches the skin
When is a therapeutic ultrasound transducer used?
Usually with physical therapy
What are 1-D arrays?
Elements arranged side by side oriented with the long axis and fired along the parallel axis
What are 1.5-D arrays?
arranged side by side oriented with the long axis but are etched parallel to the long axis to create multiple elements in the short axis.
What are 2-D arrays?
Typically have a few thousand elements. Used in 3D imaging and with linear, sector, and curvilinear transducers.
What is propagation speed in soft tissue?
1.54 mm/ms
Detail resolution is _________ and _________
axial and lateral
Axial resolution is determined by
the length of the pulse (1/2 the SPL) and pulse duration
Axial resolution is for structures ____________ to the beam?
parallel
Lateral resolution is for structures _______ to the beam?
perpendicular
Lateral resolution has to do with _______________
beam width
Contrast resolution has to do with
number of shades of grey
Temporal resolution has to do with
frame rate. The number of focuses, the number of scan lines
Which resolution is controlled by depth?
temporal
Deeper = _______ PRF
longer
Spatial resolution = __________ resolution
detail
Other names for axial resolution
depth, longitudinal, radial, range, linear
If frequency increases, axial’s numbers ________, and indicates _________ axial resolution
decrease / better
Other names for lateral resolution
transverse, angular, azimuthal
What is temporal resolution?
the ability to accurately display moving structures over time
_______ has the best temporal resolution and _______ has the worst
M-mode / color Doppler
Temporal resolution increases with
shallow depth
single focal zone
decreased pulses per scan line
narrow sector angle
decreased line density
interpolation
What is frame time?
the amount of time required to produce a single frame
________ frame time leads to ________ frame rate and _______ resolution
increased / decreased / temporal
What is slice thickness resolution? (Elevational resolution)
A measure of the beam width perpendicular to the image plane. Set by the manufacturer
The ______ the element diameter, the _____ the near zone
wider / longer
The ________ the frequency of the beam, the _______ the near zone
higher / longer
Linear array have about how many elements?
about 200
Linear arrays use _______ focusing and beam steering
electronic
What specialties use linear arrays?
abdominal, OB, small parts, vascular, and musculoskeletal
About how many elements are in curvilinear arrays?
120-250
Curvilinear arrays have _________ focusing and beam steering?
electronic
Curvilinear arrays are used in what specialties?
abdominal, OB, gynecological, small parts
About how many elements are used in phased arrays?
100-200
Phased array has _______ steering and steered
electronic
Phased arrays are used in what specialties?
cardiac, abdominal, pelvic, vascular, transcranial, and neonatal brain imaging
Vector array is used in what specialties?
pelvic, echocardiography, abdominal, transcranial, neonatal brain imaging
What is laminar flow?
Concentric layers of flow each with a slight difference in velocity. (fastest in the center, slower at the edges due to friction)
What is plug flow?
When all layers of flow are moving at relatively the same velocity (like the aorta)
What is parabolic flow?
When there is more of a difference in the velocity between layers.
What is Poiseuille’s equation about?
The relationship between pressure, flow volume, and resistance
When is Poiseuille’s equation used?
to describe how much fluid (blood) moves through a pathway (artery)
Vessel length and viscosity are relatively _________. Increases in either one will cause __________ resistance
constant / increased
What is resistance?
the rate of flow in the arteries and is regulated by the arterioles
In a resting patient, the highest resistance in the arterial system is
the arterioles
Extremities/muscles have a much ________ resistance to blood flow than the organs
higher
increased viscosity and vessel length lead to ______ resistance
increased
increased vessel radius leads to _________ resistance
decreased
As resistance increases, blood flow __________ with ____________ in pressure
decreases / no change
Stenosis causes resistance to increase ___________ to a stenosis and decreases ________ to the stenosis
proximal / distal
Pressure is defined as
the concentration of force within an area
When does pressure increase?
systole
Average pressure in the veins is _______ and in the arteries _______
2 mmHg / 100 mmHg
Arterial stenosis leads to _________ pressure as the velocity __________ with stenosis
decreased / increases
Volumetric flow rate is always _________ to blood pressure
proportional
resistance and flow rate are _________ related
inversely
What is the Bernoulli effect?
The decrease in pressure at a stenosis due to increased velocity at the site
What is antegrade?
moving forward in the direction of blood flow
what is retrograde?
backward flow or filling, or against the normal direction of flow
what is turbulence?
disrupted flow cause by a stenosis, tortuosity, or bifurcation, appears at the exit point of a stenosis
what is bruit?
abnormal blood flow sound in a blood vessel, can be due to stenosis; also seen with vessel branching or tortuosity
what is thrill?
abnormal flow sensation in a blood vessel (vibration), can be due to stenosis; also seen with pseudo aneurysm and hemodialysis grafts
What is pulsatility?
continuous throbbing or beating, flow in the arteries pulsates due to continuous cardiac contractions, venous flow is not pulsatile because it is not moved by cardiac contraction
What is capacitance?
the ability of veins to store blood
Why are veins considered the capacitive vessels?
because of their increased compliance and ability to store larger volumes of blood than arteries
What is hydrostatic pressure?
weight of the column of blood inside the vessels
What is transmural pressure?
pressure within the veins pushing outward. (normally low)
______ and _____ are responsible for moving flow through the venous system
respiration / muscle contraction
Which increases venous return to the heart from the upper body, inspiration or expiration?
inspiration
What is the Doppler shift?
the mathematical difference between the transmitted and received frequencies, occurs when structures are moving towards or away form the listener
Doppler shift is directly related to ____________, __________ of red blood cells being sampled, and the ___________ between the US beam and blood flow
transducer frequency / velocity / cosine of the angle
The angle between the ________ and the ________ must be known to determine an accurate Doppler shift
US beam / blood flow
Doppler shift is inversely related to the _________
speed of sound in the medium
Doppler measures ______ not _________
velocity / speed
A low pass filter does what?
Eliminates the signal from the blood and only shows color information representing wall motion (color Doppler)
Larger packet size causes ___________ frame rates but produce more __________ flow velocity information
decreased / accurate
Larger packet sizes are better able to identify ________ flow more accurately
low velocity
What is autocorrelation?
automatically correlates data from multiple sampling sites. assesses the data from multiple sampling sites and produces a display representing mean flow velocities
What is packet size?
the number of pulses per scan line within the color gate.
Flow needs to be __________ to the beam. Never _________
parallel / 90 degrees
What is power Doppler?
Doppler mode in which the signal is determined by the amplitude of the shift, not the shift itself. Amplitude is directly proportional to the number of red blood cells.
How is power doppler imaging different than color doppler imaging?
Power doppler measures the energy variance not the frequency shift. It is not angle dependent
Power doppler is very __________, it is ideal for ______________, but also makes it more susceptible to __________
sensitive / slow, small vessels / patient or organ motion
For CD, PD, PW, and CW signals, ___________ are customarily used to eliminate the small doppler shift caused by movements of other tissues
high-pass wall filters
What is spectral doppler?
Doppler shifts are detected along a single line and used to produce a graphic representation of the blood velocities
How does PW Doppler work?
Using controlled time intervals between transmitted and received sounds to collect information using a single PZT element
Aliasing is the biggest disadvantage of PW Doppler because…
it limits the velocities that can be evaluated
Doppler shift is _______________ related to the transducer frequency
directly
The best incident angle to produce the most accurate Doppler shift information is
0 degrees (or 180 degrees)
The best obtainable incident angle that is most commonly used to provide Doppler shift information is
60 degrees
A 90 degree Doppler incident angle will demonstrate ________
no flow in either direction
An insonation angle less than 90 degrees will result in _________ shift
positive
an insonation angle greater than 90 degrees will result in _______ shift
negative
What does adjusting the color gain do?
adjusts the displayed amplitude of the reflected frequency shift from the flowing blood.
Setting the macine to a proper color gain involves what?
increasing the gain until blossoming is noted and then decreasing to just below that level
What is the optimum color angle sample between the sample box and the blood flow
0 degrees or parallel to flow
What happens as the incident angle moves closer to 90 degrees?
color Doppler display will decrease until it is absent
More _______ structures provide better color display with _____ frame rates and ______ temporal resolution
superficial / faster / improved
What is the color packet size?
also known as the ensemble length. The packet size refers to the number of samples taken during evaluation
What does the wall filter do?
Eliminates low frequency Doppler shifts from display. Used to reduce clutter/flash/ghosting artifacts. Will not eliminate aliasing
What is color priority/threshold?
determines wheter color pixels should be displayed preferentially over grayscale pixels
Lower threshold means _____
Higher threshold means _____
less color / more color
What is persistence?
temporal compounding. color sensitivity. uses the average of previous frames to create the displayed image. improves signal to noise ratio on color image
Higher persistence levels allow
prolonged display of color on the image. It is preferred for slow moving flow.
Increased persistence and sensitivity levels can aid in
the evaluation of heavily calcified arteries
For spectral Doppler, what is displayed on the graph?
Doppler shifts along a single line, used to produce a graphic representation of the blood velocities
What does the horizontal axis on the spectral graph represent?
Time
What does the vertical axis on the spectral graph represent?
Doppler shift/Velocity
What degree of angle will flow velocity be miscalculated?
20 degrees off axis
Usually a ________ cursor angle is necessary to obtain accurate Doppler information (especially in vascular)
60 degrees
What is the average size of the sample volume for arterial evaluations?
1 - 1.5 mm
What is the standard sweep speed setting for spectral Doppler display?
50 mm/s
Anytime a monophasic waveform is seen in an _____ it is abnormal
extremity
anytime a biphasic/triphasic waveform is seen in an _______ it is abnormal
organ
What is resistive index?
Doppler measurment used to quantitate the resistiveness of the distal bed.
When is resistive index used?
to evaluate arterial stenosis
What is pulsatility index?
Doppler measurement used to determine how pulsatile a vessel is over time.
How many planes/views are required to determine if it’s artifact or something more?
at least two
What is range ambiguity?
Shallow reflectors reflect sound energy that arrives at the transducer before the rest of the original pulse finishes transmitting.
What does noise/speckle degrade?
contrast and spatial resolution
What is volume averaging artifact?
also known as slice thickness or beam width artifact. The echo information from the 3rd dimension is overlapped with the echoes from the center of the beam on the image. Happens the most in deep imaging where the beam is widest.
How to correct for slice thickness artifact?
narrowing the thickness of the beam, short axis focusing, using a standoff pad, or repositioning the focal zone
What is clutter (Doppler artifacts)
Also known as color flash, color bleeding, color ghosting. Unwanted Doppler display patterns typically caused by structure motion or breathing
What is blooming or blossoming (Doppler artifact)?
Color obscures the gray scale display of soft plaque because the resolution of color Doppler is lower than the gray scale. Causes the pixel to be displayed as color instead of grey scale.
What does the x and y axis represent in M-mode?
x = time / y = depth
What does the x and z axis represent in B-mode?
x = reflector depth / z = reflector brightness (amplitude)
What does the beam former do?
Controls the timing of the signals sent to the individual elements for steering and focusing the beam
What are grating lobes?
artifacts caused by extraneous sound that lies outside of the primary path of the beam
What is apodization?
controlled by the beam former by decreasing the strength of the voltage pulse sent to the outermost elements.
What is the pulser?
part of the beam former that controls the strength, or amplitude, of the electricity striking the elements, as well as the PRF and PRP.
What does the pulser control?
The amount of power entering the patient.
What other terms mean power?
output, output gain, output power, acoustic power…
The _______ the output power, the ______ the return echo
higher / stronger
What are the benefits of increased power output?
1) higher amplitude return echoes for a better signal-to-noise ratio.
2) improved depth penetration
How can the sonographer adjust the output power?
adjust the control stating output, power, or transmit.
What is frequency compounding?
Soft tissue is imaged at various frequencies and averaged. The displayed image is the result of all the frequencies and is another way to produce the image with improved contrast resolution and reduction in noise and acoustic speckle.
What is the master synchronizer?
The part of the machine responsible for controlling the timing of the echoes. It tells the pulser to send out a pulse and pays attention to when the echoes come back to determine their range.
What is harmonics?
harmonic signal produced by the patient’s tissue that is a multiple of the fundamental frequency. Harmonics are only generated as the beam travels deeper. (2F is used)
If a 2 MHz beam is sent into the patient, with harmonic imaging, what signal is sent back?
4 MHz
What type of resolution is improved with harmonic imaging?
lateral resolution
What is the receiver?
Where the return signal is processed. (preampfication, amplification, compensation, compression, demodulation, and rejection)
What is amplification?
overall gain. increases or decreases the strength of all the returning echoes equally
What is compensation?
time-gain compensation. compensates for the fact that attenuation occurs, and the more distant echoes are increased in brightness to achieve a uniform level of brightness.
What is compression?
the function of the receiver that decreases the range of signal amplitudes present within the machines receiver.
What is dynamic range?
The series of echo amplitudes present within the signal. Inversely related to compression.
What is demodulation?
processes the signal to make it easier for the machine to handle. (Rectification and smoothing)
What is rectification?
Turning negative voltages into positive voltages
What is smoothing?
wrapping an envelope around the signal to make it less bumpy or remove the humps.
What is rejection?
discards signal amplitudes below a certain threshold to reduce image noise
What is the transmit/receive switch?
Ensures the electrical signals travel in the correct direction. It ensures the pulser voltages go to the transducer, and the received voltages from the transducer go to the signal processor (receiver)
What is the scan converter?
part of the machine that makes grayscale imaging possible and is responsible for storage of the image data.
Signals travel from the receiver to the __________ and then to the scan converter/image memory, and then to the _______
analog to digital converter / digital to analog converter
What is preprocessing?
where incoming signals are assigned shades of gray based on their amplitudes. Happens before the scan converter. Images are still live at this point.
A ______ is the smallest amount of computer memory possible.
Bit
_____ bits make 1 ______
8 / byte
The more pixels on display, the better the ______ resolution
spatial
What is write zoom?
a pre-processing function, enlarges the image by redrawing it. High quality zoomed image
What is read zoom?
a post-processing function, enlarges the image by magnifying the pixels. Offers a coarser, less optimal type of zoom.
What is spatial compounding?
Eliminates edge shadowing because the object is imaged at different angles.
What does spatial compounding reduce?
speckle artifact and reverberation
What is the purpose of the damping material?
to shorten the length of the pulse by decreasing the number of cycles in the pulse
What is sensitivity of the transducer?
the ability of the system to display low-level or weak echoes.
What is bandwidth?
the range of frequencies present within the beam
The more damping there is, the _______ the pulse, the ______ the bandwidth, the _____ the QF
shorter / wider / lower
What is the quality factor?
the measure of the beam purity. the operating frequency of the transducer divided by the bandwidth
What is elevational resolution?
the resolution in the third dimension of the beam. the slice-thickness plane
