does an unfocused transducer have a natural focal zone?
yes
all of today's scanning is
automated electronic
electronic scan heads have multiple active __________ , each of these is connected by a wire to the US system
elements
the elements are shocked in sequence, one after the other
sequencing
the elements are shocked in a certain pattern with minute time differences between
phasing
all arrays are
phased focused
always means multiple elements
array
Linear Sequenced Arrays scan lines are _______ to transducer
perpendicular
linear image shape does not need
beam steering
linear sequenced arrays have the ability to electronically (phase) steer the beam for
- color/spectral Doppler steering-transition to wide-field-of-view (vector) image shape
for regular 2D imaging, no __________ _____________ is needed
Beam Steering
variation of a linear sequenced array, but produces a curvilinear image
curved sequenced array
produces a sector or vector image
phased array
uses electronic focusing and steering (phasing) , and contains NO moving parts
Phased Array
Phased Arrays
focusing and steering controlled by delaying the electronic impulses to the elements
sends pulses out rapidly & repeatedly to create a frame of ultrasound and is done by phasing
electronic beam steering
IVUS
intravascular US
transducers used with open and laparoscopic surgery
intraoperative
how can an electric beam be steered
by delaying/timing the electrical impulses that control the elements
how can an electric beam be focused
by delaying/timing the electrical impulses that control the elements as well as steered
Dynamic Aperture is used to improve
lateral resolution
Dynamic Aperture
system changes # of active crystals that are firing to change with of beam at various depths
Dynamic Focusing produces
a shorter, stronger return echo
2-D B-Mode images stacked up to form _____ image
3-D
3 types of 3-D images
free-hand , automated , 2D array
free-hand cannot measure
volume
automated
curvilinear or linear transducers mounted to a motor
2D array
is all electronic, acquires volumes and is aka "x-matrix
4-D
is real-time 3-D
volume imaging is called
2D array
2D array
real-time volume and has no moving parts
spatial compounding
eliminates edge shadows and reduce speckles
the transmitted frequency is also called the
fundamental frequency
the sound that comes back to the transducer (from the tissue) is ...... and is called what
double the fundamental frequency , the second harmonic
harmonic frequencies are generated by
tissue, not by transducer
THI waveform leans more as it travels, therefore the signal gets ________ with _________
stronger , depth
what is filtered out with THI
the fundamental frequency
with THI the primary beam is much barrower, improving this resolution
lateral
what reduces grating lobes and artifacts
THI
ultrasound contrast
microbubbles
microbubbles
shell filled with an inert gas that causes a significant impedance mismatch (larger reflection/stronger signal)
the shell of contrast enhanced ultrasound can be made up of 4 things
albumin , galactose , lipid , or polumers
the gas core (3) and size of CEUS
air, perfluorocarbon, or nitrogen1-4 um (micro)
what are the 2 kinds of resolution
spatial and temporal resolution
spatial resolution subtypes
axial , lateral , elevational
the smallest distance 2 reflectors can be next to each other and still show up as 2 independent return echoes
axial resolution
with AXIAL RESOLUTION, where are the 2 reflectors in regard to the sound beam
parallel to sound beam
synonyms for Axial Resolution
LARRD ( longitudinal, axial, radial, range, and depth)
what determines the axial resolution
spatial pulse length (SPL)
SPL =
# of cycles (n) x wavelength
the shorter the SPL the
better two reflector can be
decreasing the SPL is better for this resolution
axial
axial resolution is best with
high frequency, tightly damped transducers
axial resolution of .1mm is (better or worse) than axial resolution of .3mm
better (the smaller the better)
the distance between the reflectors must be ________ to or _______ greater than the axial resolution
equal , greater
axial resolution =
1/2 SPL
axial res can be improved by decreasing
wavelength
the ability to send an US pulse between 2 reflectors perpendicular to the beam and NOT receive a return echo
lateral resolution
if an echo is generated when we are aiming at space there is poor
lateral resolution
Synonyms for lateral resolution
(LATA)lateral, angular, transverse, azimuthal
lateral res is improved by DECREASING
beam diameter (width)
aperture
diameter of the element
with Lateral Res, at the end of the near zone the beam aperture =
1/2 the aperture
with Lateral Res, at two near-zone lengths, the beam aperture
equals the aperture
with lateral res, the smaller the number the (better or worse)
better
smaller diameter probes with lower frequency have a ______near zone, and ______ divergence in the far field
shorter , more
larger diameter probes with higher frequency have a ________ near zone, and ______ divergence in the far field
larger , less
increased aperture =
longer NZL
increased frequency =
longer NZL
lateral res may be improved by decreasing the
beam diameter
slice thickness is also called the
elevational plane OR partial volume thickness
slick thickness is focused usually with a
mechanical lens
the _______ the slice thickness the better
thinner
these transducers can electronically focus in both scan plane as well as the slice-thickness or elevation plane
1.5D transducer
1D array
elevational plane focused mechanically, with a lens
1.5D array
elevational plane is focused electronically
2D array is a type of
realtime 3D probe
temporal means ______ , and is also known as
time , frame rate
the ability to correctly display moving structures in real-time
temporal resolution
increased depth causes __________ frame rate "PRF
decreased
increased focuses causes _________ frame ate "PRF
decreased
one complete image on the screen is called
one frame
the less focal zones the better it is for temporal res (T or F)
true
what negatively affects frame rate (temp res) ?
- multiple focal zones- # of scan lines (want a narrow sector size)- increased depth
if the frame rate stays the sane but the depth was increased, what happened?
the # of scan lines per frame must have decreased
What is PRF inversely related to?
depth