midterm Flashcards
what array transducer fires all of the elements for each acoustic scan line, using small time delays to steer the beam?
phased array
the term signal to noise ratio denotes
the relative amplitude of the signal compared to the amplitude of the noise
what technique would be most likely to produce grating lobes in your image?
beam steering
during the performance of a sonographic exam, yo would be most likely to encounter refraction in this view
curved interface
if you increase the prf and leave all other controls unchanged, what will happen?
frame rate with increase
which control is not user adjustable?
echo arrival time
you have expanded the image sector width to improve visualization, what can you do to maintain the same temporal resolution
decrease the number of focal zones
which control would you adjust to alter the dynamic range of the displayed echoes?
compression
what interaction of US and tissue is primarily responsible for imaging internal structure of organs
scattering
what can you do to improve the temporal resolution while scanning?
decrease the acoustic scan line density
you are imaging a 3D dataset that has anisotropic resolution. what does this mean?
unequal resolution is present between imaging planes
what is the advantage of using a water path scanner?
near field reverberations are reduced
what type of resolution is determined by the number of pixels in the scan converter?
spatial
you are imaging a rounded mass with irregular borders, the mass has a much slower prop speed than the surrounding tissue. what interaction will be encountered?
all of the above. refraction, reflection, absorption, scattering
what type of focusing is performed by delay circuitry upon reception?
dynamic receive focusing
selective reception of echoes generated within the body by nonlinear propagation describes?
tissue harmonic imaging
which helps to improve the Elevational resolution in a B mode image?
focusing with an acoustic lens
requirements of magnetic field tracking for 3D reconstruction include which of the following?
all of the above
you notice a loss of detail in the lateral dimension of the US image. how do you improve this?
increase the scan line density
the US system in your lab has a transducer with a small footprint. what disadvantage does this transducer have?
resolution is degraded at large distances
if you wish to use an array transducer that allows you to control transmit focal depth, what type would you select?
any of the above
while scanning a curved structure, you notice shadowing at the lateral edges of the structure. what is required for this artifact to occur?
different media propagation speeds
all of the following are limitations of M mode scanning except?
motion axial to the transducer is not displayed
the spatial resolution of the scan converter is determine by?
number of pixels in the scan converter matrix
what information is present in M mode display?
time, motion pattern, and amplitude
where are images stored in the US system?
scan converter
varying the excitation voltage to each element in the group used to form the US pulse is called?
apodization
you have increased the transmit power while performing a pelvic exam, this action increases what?
all of the above
which of the following describes an analog signal?
continuous variation of the signal is possible
what receiver function is responsible for decreasing the difference between the smallest and largest received signal amplitude?
compression
increasing what will improve axial resolution
frequency
what control converts numbers stored in memory to proportional voltages?
digital to analog converter
what component is necessary for a real time B mode scanner but is not present in A mode?
scan converter
what is the unit for sound intensity?
decibel
axial resolution is improved with?
all of the above, increased bandwidth, shorter pulse length, and shorter wavelength
when you freeze an image, where is the echo information stored?
scan converter
a digital scan converter is another name for
image memory
you will not see refraction if…
the sound beam is perpendicular to the interface
in order to focus a sound beam relatively far away from the transducer, it is advanegeous to?
increase the diameter of the element
what will not improve axial resolution
increased frequency
which describes the best resolution for modern day US scanners?
axial resolution
what benefit would you obtain by choosing a transducer having a large diameter compared to having a small diameter?
it can focus at greater depths
how do you eliminate grating lobes?
reduce or eliminate beam steering
increasing the dynamic range setting affects the US image by?
decreasing image contrast
audible frequency range
10kHz
Which system function is limited by the speed of sound in tissue?
PRF
shadowing is a form of what?
reflection
dynamic receive focusing uses?
time delays before echo signals from array elements are combined
prop speed error occurs in which sonographic appearance?
improper axial resolution of an echo
what improves lateral resolution?
increased aperature
what can you adjust to improve signal to noise ratio?
persistence
acoustic impedance =?
density times prop speed
how is electronic noise reduced?
rejection
when the ac is high?
adjust your compensation
correct order?
transducer, receiver, scan converter, display
prop velocity depends on?
density and compressibility
how many levels can a single bit represent?
2
which scanning mode doesn’t rely on echo ranging?
transmission
which least influences axial resolution?
beam width
the rate of sound attenuation is lowest in?
water
which artifact will result in both lateral and axial displacement?
multipath reflections
what would decrease frame rate?
increasing acoustic scan line density
Dynamic apodization is a method employed to?
reduce side lobes
attenuation of the sound beam increases with increasing what?
all of the above
which of the following doesn’t affect impedance?
frequency
which would increase the SPL?
increased number of cycles per pulse
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
you can reduce the beam width to improve spatial resolution in the image by which of the following?
focusing
if you increase the PRF, to a level too great for the depth of field, this result will be?
range ambiguity
what happens when you change the transmit frequency?
number of cycles per second is altered
what type of resolution is mostly affected by electronic focusing and dynamic aperature?
lateral resolution
complete destructive interference of echo reflections will affect the display in the following way?
by creating black pixels
which of the following is not a function of the receiver?
dynamic aperature
what affect will you detect in the image if you increase the threshold control?
decreased appearance of weak echo signals
the bands have decreasing brightness with depth, what artifact are you seeing?
reverberation
what the difference between frequencies used for Doppler and for B mode?
the frequency for Doppler is usually lower than for imaging
the incoming raw echo signals must be compressed into a smaller dynamic range because?
the display cannot accommodate the wide dynamic range of the incoming signals
what would you adjust to increase the intensity of the transmitted pulse?
output power
interference patterns of reflected waves cause?
acoustic speckle
by increasing the image depth and scan line density, this results in?
reduced temporal resolution
how can you demonstrate tissue boundaries that are not perpendicular to the sound beam?
spatial compounding
what is a typical frame rate for B mode real time imaging?
10-50 Hz
