Transducer Evolution Flashcards
mechanical transducers (thickness, shape, diameter)
thin
disk shaped
6-19mm diameter
mechanical transducers had a ____ focal zone
fixed
4 types of mechanical transducers
linear translation
wobbler
oscillating element
oscillating mirror
linear translation
mechanical transducer
oldest
moved the crystal assembly along a track to “sweep” the tissue
wobbler
mechanical transducer
motor rotated back and forth to obtain sector type image
fluid filled=risked bubble production
oscillating element
mechanical transducer
crystals oscillate and mirror reflects to get linear FOV
oscillating mirror
mechanical transducer
mirror moves with a stationary element to get a linear FOV
rotating wheel probes
several crystals spin and only pulse when the element passes the FOV
FOV
field of view
annular array was important why (hat stayed the same and what changed)
probe still mechanically steered but the ability to dynamically change the focus was now possible
the annular array uses what shape of crystal and what was the purpose of the shape
concentric discs ( one crystal cut into rings)
by changing the disc fired, you change the diameter= varies the focal depth
the diameter of the crystal changes the ______
focal depth
grating lobes (annular array)
low energy beams that radiate away from the main axis and contribute to artifacts in the image
what is phasing
phasing uses nanosecond time delays to change when the voltage excites the crystal
what is the purpose of phasing
to control the beam (Huygen’s principle) and allow for beam focusing and steering
focusing and steering are accomplished with the _____ of the voltages to the crystal in the _____ probes
phasing
electronic array
what is another term for describing steering the beam
Vector scanning
_____ of waves hit with a voltage at different times causes steering of the beam
interferance
the steered beam goes in the _______ (opposite or same) direction as the delay
opposite (hit right crystal first beam is steered to the left)
delay /
/
beam \
direction \
sector phased array: all crystals are fired at ______ time to steer the beam across the face of the probe
nearly the same
the sector FOV can be as large as ___ or as small as ___
90 degrees
30 degrees
linear probes tend to have relatively _____ footprints with approximately ____elements arranged in a row
large
64-200
The FOV of a linear probe is _______ shape but can be ______ if scanning in a ____ mode
rectangular
trapezoidal
vector
what is scan line divergence
space between the lines
is there scan line divergence in linear array probes
no
firing a small single element will ______ divergence = ____ beam = ____ resolution and sensitivity
increase
broad
poor
firing a single element takes away our ability to electronically ____ or ____ the beam
focus
steer
the larger the point source of sound, the ____ the divergence and the resolution and sensitivity would _____
smaller
improve
firing in ____ enables electronic transmit focusing and steering while decreasing the divergence
segments
what is segmental sequencing and what does it help with
a group of crystals is fired to create a beam followed by a second group that is one crystal down in the row and it helps so that we don’t sacrifice information in a linear/curved linear
first group is crystal 1,2,3
second is crystal 2,3,4
third is 3,4,5
etc
two advantages to curved linear probes
large footprint and FOV (possible to see well in near and far field)
disadvantage to curved linear probes
resolution in the far field can be degraded as the distance between the beams is increased
what is the process called that corrects grating lobes
apodization
what is apodization and what does it help
voltages to the crystals are gradually weakened from the inside out
helps prevent grading lobes
2 ways to obtain 3D/4D images
freehand using traditional array probe
Volumetric probe
what is a volumetric probe (how does it create image)
beam is swept over are of interest (electronically or mechanically) to obtain info for 3D reconstruction
pixels =
voxel=
picture element
volume of pixels
3 spatial res types
axial: up/down
lateral: R/L
elevational: front/back (thickness)
how is 4D different to 3D
it is 3D but at real time
1.5 probes are different to 1 how
they have 1 interface plus Z axis focus at 2 levels (on either side of of crystals)
how big are the Z axis focus levels on a 1.5 probe
1/2 thickness of og crystal
intravascular probes
scan from within a vessel/lumen
transesophageal echo probes
improve visualization of heart by swallowing probe and imaging from within the esophagus
dedicated CW probes contain 2 crystals where one ___ and the other ____
transmits
receives
dedicated CW probes are ____ backed and have a continuos _______ voltage
air
AC driving
in vascular a CW probe is called
pencil probe
in echo a CW probe is called
ped-off probe
what are the four different ways to refer to the transducer Q factor
- resonant f/bandwidth
- mechanical coefficient
- energy stored/energy lost
- reciprocal of fractional bandwidth
