SPI review 3 Flashcards
a mode
amplitude mode
dot moves accross screen and measures distance between probe and reflector
a mode x axis
reflector depth, measured by pulses time of flight
a mode y axis
ampliude of echo, measured by echo strength
b mode
brightness mode, returning echoes are presented as spots on the line of travel of the emitted US pulse. stronger returning echoes the brighter the spot. brightness of dot is proportional to the amplitude of the returning echo
b mode x axis
reflector depth, measured by the pulses time of flight
b mode z axis
brightness of the dot, measured by reflection of amplitude
there is no __ _____ with b mode
y axis
m mode
motion mode or t m mode, the only mode that displays the changing position of reflectors with respect to time
m mode x axis
time
m mode y axis
refelctor depth, measured by pules time of flight
narrow beams provide
high quality imaging and good lateral res
2 d images aka
b scans b modes cause they are grey scale
mechanical scanning # of crystals and shape
scan head contains one disc shaped element
mechanical scanning steering
pzt moved by a motor, oscillating crystal or mirror through a pathway, automatically creating a scan plane
mechanical scanning focusing
conventional or fixed, curvature (internal) of PZT or an acourstic lent 9External) focuses the beam at a specific depth
mechanical scanning image shape
fan or sector shaped, scan lines diverge or separate with depth
mechanical scanning defective srystal
destroys entire image
a collection of active elements in a single transducer
array
array element
a single slab os PZT cut into separrate pieces called elements
array channel
a combination of electronic circuitry, the wire and the element
a group of ringed elements (bulls eye) with a common center
annular array
a collection of elements in a line
linear array
two types of linear array
linear switched aka sequential array
linear phased array
elements arranged in an arc
convex, curved or cuvilinear array
two types of convex, curved, curvilinear array
convex switched aka sequential array
convex phases array
of crystals and shape for linear switched aka sequential arrays
large transducers w/ approx 200 rectangular shaped elements arranged in a line
what improves lateral res w/ linear switched aka sequential arrays
a few (5-10) of the elemtns are fired at the same time to create a narrow direction beam
linear switched aka sequential arrays steering
no steering, pulses sent down parallel lines, the scan lines are parallel and are wqueally spaced
linear switched aka sequential array focusing
fixed lens (external) or curved crystal (internal)
linear switched aka sequential array image shape
rectangular shape, no wider than the transducer
linear switched aka sequential array defective crystal
dropout extending from superficial to deep
adjustable focus or multi focus acheived electronically
phases arrays
of crystals for phased arrays
approx 200 rectangual shaped elements in a line
phased arrays steering and focusing
a collection of electric pulses is delivered to all the elements in various patterns, focusng and steering is electronic
electronic signals excite ___ of the elements and create only ___ _____ _____
all
one sound pulse
the phasing patterns
focus and steer the sound beam during transmission (nearly simultaneously, 10ns apart)
phases arrays image shape
sector or fan shaped
phased array defective crystal
if one element malfunctions the steering and focusing become erratic
electronic slope creates
beam steering
electronic curvature creates
beam transmit focusing
a convex or D shaped firing patter creates a
defocused or divergent beam
allows focusing at many depths by delays during reception optimizing image quality
dynamic receive focusing
annular phased arrays # of crystals
small number of ring shaped elements
annular phased arrays use inner crystals for
shallow regions and outer crystals for deep regions
annular phased arrays have small diameter rings which have
a shallow focus but diverge rapidly
annular phased arrays have large diameter rings which
have a deep focal length
annulary phased array image shape
sector or fan shaped
annular phased arrays steering
mechanically, unlike other phased array transducers
annular phased array focusing
multi focusing provides electroinic focusing in all planes at all depths, a core sample, this provides optimal lateral res at all depths throught the image
annular phased array defective crystal
horizontal band dropout
pzt arranged in a curve to provide natural sector image
convex aka curved arrays
convex aka curved arrays may be ____ or ______ just line linear array
sequential or phased
of crystals for convex aka curved arrays
approx 200 rectangular shaped crystals
convex aka curved arrays shape
blunted sector, fan shaped image
a for of electronic receive, electronic focusing
dynamic aperture
how does dynamic apeture work
as returning echoes hit trans, the size of the trans surface listening for echoes is varied by varying the numver of elements used to receive the reflected signal
dynamic apeture allows the receive beam to be __________ at all depths, and optimized ______ res at all depths
as narrow as possible\
lateral
2 d arrays create
3 d images
of elements in 2 d arrays
can have thousands in up and down and side to side directions
allow focusing in the plane of the beam width
1 1/2 dimensional arrays
improves ______ res by making __ _______ ______
elevational
a thinner slice
combine linear sequental and linear phased array technologies
vector arrays
vector arrays image shape
trapezoidal, a sector with a flat top that does not come to a point
what is an advantage of 1 1/2 dimensional arrays
reduced slice thickness
seeing diff ray shades in an image
contrast resolution
seeing detail in an aimage
spatial aka detail resolution
the ability to accurately locate moving structures at any particular instant in time
temporal res
temporal res is determined by
frame rate, higher the better
units for frame rate
hertz (per sec)
frame rate determined by
imaging depth
number of pulses per frame
frame rate and imaging depth are _____ related
inversley, shallower depth higher frame rate
frame rate and number of pulses are _____ related
inversly, fewer pulses higher frame rate
frame rate is limited by
speed of sound in a medium and depth of view
since the sonographer can adjust the depth of view but not the speed of sound in the medium, the speed of sound is a
fundimental limitation to frame rate
4 factors under sonographer control that affect temporal res
max imaging depth
of pulses per scan line (multi focus systems)
sector size
line density (lines per angle of sector)
when line density is low ______ res improves but ______ res degrades
temporal
spatial (detail)
multi focusing degrades _____ res but improves ______ res
temporal
lateral
temporal res and image quality are ______ related
inversly
FR
frame rate
Tf
time to create a frame
FR and Tf are
recipricals
the sector size changes from 90 to 45 but the frame rate ramains the same, what else happened
the line density was doubled
what is the frame rate is each image of ultrasound system is created in 0.02 seconds?
50Hz, cause 0.02 is 1/50th sec, Ft is reciprical of FR
what is the time needed to make a single image if the frame rate of US is 20Hz
0.05sec, cause reciprical of 20Hz is 1/20 which is also 0.05
US system components
master synchronizer
transducer
pulser
receiver
display
storage
communicates with all of the individual components of the US system. organized and times their functions so as to operate as a single integrated system
master synchronizer
converts electrical into acoustic energy and vise versa
transducer
controls electrical signals sent to the trans for sound pulse generation. deterines the PRF, pulse amplitude, and pulse repetition period. creates the firing pattern for phased array systems which is called the beam former
pulser
the electronics associated with processing the electroinc signal produced by trans during reception and creating image for display
receiver
associated with the presentation of processed data for interpretation
display
archive the US data
storage
pulser function
recvs timing signal from synchronizer
creates electrical signal that excites pzt
produces electrical voltage 10-500 volts that excites pzt
continous wave pulser mode
electrical freq=usfreq
the pulser is not called the beam former for what
phased arrays
transducer output aka output gain acoutic power pulser power energy output transmitter output is determined by what
excitation voltage from the pulser
pzt vibrates with a magnitude related to
pulser voltage
weak signals returning are boosted by what
receiver
receiver functions in order
amplification compensation compression demodulation rejection
purpose is to increase strength of signals in receiver prior to further processing
amplification
aka
recaiver gain
amplification changes the
brightness of the entire image
signal to noise ratio is _____ when amplification levels change
unchanged
used to create image of uniform brightness from top to bottom, makes all echoes same regardless of depth
compensation
compensation aka
time gain compensation
depth compensation
swept gain
what will you adjust is you cannot see reflectors in the near or far field on the image?
TGC
reducing the total range, the smallest to the largest signal and allows us to see all gray shades is
compression
compression decreases the ____ ______ of the signals
dynamic range
compressions effect on image
changes the gray scale mapping
how to calculate changes in dynamic range and its units
dB
add or subtract, from begining range
is compression adjustable by sonographer
yes
changes the signals form to one more suitable for display
demodulization
is demodulization adjustable by sonographer
no
turning all negative voltages into positive ones, corrects for or eliminates negative voltages
rectification
putting an envelope around the bumps to even them out
smoothing
displays low level echoes only when clinically meaningful, used to eliminate low level noise in out images, but does not affect bright echoes
rejection aka suppression and threshold
what degrades due to the image being too bright due to output power
lateral and longitudinal res
harmonics are
multiples of the freq
harmonics are created in
the tissues, not in the trans or receiver
__ ______ behavior creaste hamonics
non linear
what creates harmonics
sound moving slower in rarefactions and faster in compressions, this small difference in speeds is known as non linear and distorts the sound wave to create harmonics
positive and negative pulses are transmitted down each scan line
form of harmonic imaging called pulse inversion
disadvantage of pulse inversion imaging is
frame rate if 1/2 that of fundamental imaging
pulse inversion degrades ___ while improving ______
temporal
spatial
pulse inversion harmonics uses
wide bandwidth or broadbaned transducers
