ultrasound transducers Flashcards
What can you do to improve contrast res increase sector width decrease number of focal zones use a 2D or matrix array use a phase array used a curved array
use a 2D or matrix
they have both rows and columns, it allows electronic focusing in the out of plane dimension with resulting slice thickness thinner compared to 1D
a method used to improve frame rates with multi zone electronic focusing is termed: apodization parallel procesing f-number focusing low q xducer none of the above
parallel processing
aka coprocessing; frame rates can be improved by simultaneously acquiring data for multiple acoustic scan lines
when increasing the number of transmit focal zones to improve spatial res, the trade off is: lateral res vs axial res spatial res vs contrast res lateral res vs temporal res contrast res vs frame rate elevational res vs frame rate
lateral res vs temproal res
ea transmit focus requires a pulse/listen cycle; more focal zones decreases frame rate; temporal res is related to frame rate
what type of res is affected by PD lateral res contrast res temp res axial res elevational res
axial resolution
what component of a PW xducer helps to reduce the SPL and improve axial res? matching layer lens element backing material radiofreq shield
backing material
it reduces the length of time the crystal rings
the matching layer b/w the pat element and the tissue is designed to:
insulate the pt from the hot element
reduce the vibration of the xducer
reduce acoustic imped mismatch b/w element and tissue
increase the reflection coefficient at xducer-skin interface
decrease SPL
REDUCE ACOUSTIC IMPEDANCE MISMATCH B/W ELEMENT AND TISSUE
there is a large acoustic impedance mismatch b/w crystal and tissue. This would result in large reflection with little energy transfer into body
what type of xducer could you choose to produce a beam that is symmetrical about the beam axis annular array linear sequenced array phased array curved array tightly curved array
annular array
its a round xducer where elements are arranged concentrically and creates a cone shaped beam that is symmetric in all dimensions
what is an advantage of a single crystal or pure wave crystal xducer lower freq at higher res absence of aliasing with PW higher frame rates wide bandwidth greater steering angles
wide bandwidth
what is the optimal thickness for the matching layer equal to thickness of crystal 1/4 wavelength 1/2 pulse length 2x transducer diameter 1/2 width of backing material
1/4 of a wavelength
dynamic apodization is a method employed to:
focus beam at multiple depths on transmit
focus the beam at multiple depths on receive
reduce side lobes
reduce beam width in z axis
steer beam
reduce side lobes
what is the purpose of curving the xducer elements or applying a lens over the elements
provide focusing in out of plane (elevational) direction
to reduce acoustic imped mismatch b/w crystal and skin
reduce crystal ringing and improve axial res
help reduce electronic interference
all of the above
provide focusing in the out-of-plane direction
a wide bandwidth xducer w/ multiple transmit freq; which freq should you select for max penetration 3 MHz 3.5 MHz 4 MHz 5MHz penetration not affected by freq
3 MHz
with a standard 1D linear array, what type of res is affected most by electronic focusing and dynamic aperture
lateral res contrast res temp res axial res elevational res
lateral res
lateral res is improved at depth by increasing transducer width or aperture size in an array; the larger the aperture the smaller the beam width at the focal point
what type of xducer has the same measurement for elevational and lat res
convex linear array phased linear array annular array sequential linear array mech sector
annular array
if the # of cycles in the transmitted PW is inc
axial res is degraded lateral res is degraded SPL becomes shorter rate of attenuation is inc penetration is decreased
axial res is degraded
axial res is proportional to pulse length. it degrades as pulse length inc
the transducer you are using is an array assembly. what is the advantage?
xducer arrays pruduce pure, single freq beams
xducer arrays enable mech steering
xduce arrays produce long pulses for improved axial res
xducer arrays have greater dynamic range, = more shades of grey
xducer arrays enable electronic focusing and steering
xducer arrays enable electronic focusing and steering
arrays use multiple elements rather than a single to form the beam.
axial res is improved with inc bandwidth shorter pulse length shorter wavelength b & c all of the above
all of the above
which of the following is not assoc. with a low-q transducer
wide bandwidth multifreq selection long pulse length diagnostic pw u/s loss of most energy in first few vibrations
long pulse length
xducers used for diagnostic u/s are low-q xducers. they have wide bandwidth which allow multi freq selection. they have short pulses for good axial res; the short pulse results in most of the energy within it is lost after first few vibrations
you suspect that a bright spot on the b-mode is a calcification, but there is no postieror acoustic shadow. how can you optimize your system to demonstrate a shadow distal? move focal zone below hyper echoic focus increase xducer freq increase acoustic power output increase dynamic range decrease scan line density
increase xducer freq
if the sound beam is wider than the stone a shadow may not occur because tissue on either side will send back reflections for that depth
what is a side lobe
uneven xducer element
accessory pulse used for electronic steering
sound beam emitted from the xducer that travels in a diff direction from main beam
nonlinear propagation of the sound beam
additional backing material on the xducer edge used to reduce lateral vibrations
sound beam emitted from the xducer that travels in a diff direction from the main beam
inc which of the following will result in improved axial res? PD Pulse length Freq period Focusing
freq
axial res is improved by reducing pulse length or PD
what is the advantage of using multiple transmit focal zones? inc lateral res inc temporal res inc elevation res inc axial res all of the above
inc lateral res
which probe would provide best axial res to measure thickness of small structure? 5MHz linear array 7MHz linear array 10 MHz linear array 5 MHz curved arrray 5MHz phasyed array
10 MHz linear array
axial res improves with inc freq
what is the f-number?
aperture multiplied by number of elements in xducer
number of xducer elements divided by fraunhofer zone
beam width 1 cm from xducer surface
focal length divided by aperture
focal length multiplied by number of elements in xducer
focal length divided by aperture
which factor least influences axial res> damping freq beam width PD pulse freq
beam width
beam width affects lateral res
what disadvantage is related to the use of a tightly curved array? axial res degrades w/ depth field of view compromised temp res compromised lateral res degrades elevation res compromised
later res degrades w/ depth
scan lines become spaced farther apart in far field compared to near field
what res is most affected by mech. focus on a linear array xducer? elevational res lateral res contrast res temp res axial res
elevational res;
determined by slice thickness; measure of beam width perpendicular to imaging plane
