Transducer Scanner
Arrangements
Types


Mechanical
Electronic Transducers

Linear arrays

Convex linear array

Phased arrays

Vector array

Annular array
Mechanical


Used a mechanically steered fixed-focus
crystal that produced a sector image
Crystal rocks or rotates through an arc
sweeping the beam back & forth over the
region being scanned
crystal
Single crystal is rocked
back & forth forming a
15-60° sector-shaped
image
crystals
Rotating system using
multiple crystals that
rotate on a wheel to
create a curved top or
blunted sector image.
Mechanical Sector Probe
Advantages

simple & economical to manufacture

earliest of the real time probes


small footprint (good for imaging in tight
areas such as between ribs)
used in earlier TV & TR probes
TR Mechanical Probe
TV Mechanical Probe
Disadvantages









vibrated too much
electrical interference shows on monitor display
slow frame rates
fixed focal length that restricted lateral resolution &
anatomical identification
limited field of view (15-60° sector display)
near field not diagnostic - electrical noise
may create side lobes
when crystal breaks (when probe is dropped) – the
probe is useless until repaired
mechanical parts wear out
Side Lobes


weaker beams of sound traveling out from
a single element in directions different
than that from the main beam
are of low intensity, usually 60 – 100 dB of
the primary beam
Electronic Transducers


Uses electronic methods (no moving
parts) to create the image pattern
Variations in the timing delays to
elements causes steering and/or
focusing of the sound beam
Arrays



A piece of piezoelectric material cut into
separate pieces called elements; each element
has its own electrical circuit.
Individual elements are much smaller than a
crystal used in single element transducers. If
used alone these elements would produce
widely diverging beams.
Elements are grouped to increase aperture size
(crystal diameter) and decrease divergence
(create a longer near zone).
Arrays




Each element & its circuit is called a channel
# of channels dictate the # of array elements
that can be simultaneously activated to
transmit a pulse and receive echo signals
along any beam line
 channels =  lateral resolution.
Grating lobes are unique to linear-array
type transducers
Grating lobes

Summation of side lobes

 with beam steering


Cause misregistration of an object in an
image (similar to the refraction effect)
Minimized with subdicing
convex arrays are least susceptible
 phased arrays are most susceptible

Array Types

Linear arrays

Convex linear array

Phased arrays

Vector array

Annular array
Linear arrays
- have 128 (or more) elements arranged in
a line that are fired in groups of 3-5
elements to create a 2-D image that
consisting of parallel scan lines emitted
at different points along the face of the
transducer
Linear arrays




Fired in groups along the path of the array, an
image consisting of parallel scan lines creates a
rectangular-shaped image.
Width of entire image is approximately equal to
the length of the array  Beam steering not
required
Sequenced linear arrays use conventional
methods of focusing
Phased linear arrays use electronic delays for
focusing
Advantages

no moving parts to wear out

better lateral resolution

faster frame rates
Disadvantages
large footprint
creates loss of
contact with body
& cannot be used
in small windows
Linear Array Probe
Convex linear array


[Convex, curved, curvilinear] switched or
[convex, curved, curvilinear] sequenced
arrays
have 128 (or more) elements arranged in a
curved line fired in groups of 3-5 elements to
create a 2-D image that consists of radiating
scan lines emitted at different points along
the face of the transducer
Convex linear array




By firing in groups along the path of the array,
an image consisting of parallel scan lines creates
a curved-top sector-shaped image
Beam steering is not required.
Sequenced convex linear arrays use
conventional methods of focusing
Phased convex linear arrays use electronic
delays for focusing
Advantages

no moving parts to wear out

better lateral resolution

faster frame rates

larger field of view
Disadvantages
Can’t be used in
small windows
due to larger
footprint
Convex Linear probes
Phased arrays (linear phased arrays)




have 128 (or more) crystals arranged in matrix
fashion
all crystals are pulsed almost simultaneously to
produce an image scan line
Multiple, miniscule pulses steer & focus the
beam into a sector-shaped image by varying the
time delay minutely in the pulsing sequence of
the elements
they are electronically-focused & steered along
the sound path, mechanically- focused along
elevational axis
Advantages





no moving parts to wear out
better lateral resolution
faster frame rates (needed for
cardiac pump action)
larger field of view
small footprint permitting imaging in
tight windows
Disadvantages



expensive
limited near field of view
grating lobe artifacts
Phased Array
Vector Array



combine linear & phased technologies to
produce a trapezoidal-shaped image
Beam is fired across the face of the
transducer
Provides more near field & a wider sector
angle
Advantages

no moving parts to wear out

better lateral resolution

faster frame rates

larger overall field of view

small footprint permitting imaging in
tight windows
Disadvantages


Expensive
Grating lobe
artifacts
Annular array



Use concentric rings of crystals on a motor
assembly that are rotated or rocked to
create a curved-top or blunted sectortype image
Steering is mechanical, but because of
multiple crystals, electronic focusing in
scan plane and elevational planes is
possible
Annular arrays provide the thinnest beam
of all probe technologies
Advantages



superior image quality
small footprint permits tight window
imaging
narrowest beam thickness
Disadvantages



mechanical parts wear out
mechanical system requires special
engineering to provide limited Doppler
capability
vibrations from probe can be annoying to
the user & the patient
Annular Array
Beam Focusing
Transducer Beam Focusing
1. Electronic beam focusing - sequential
2. Electronic transmission focusing - phasing
Electronic Beam Focusing - Sequential

applied to individual beams for the
purpose of improving the lateral resolution
& slice thickness within the focal zone
Electronic Transmission Focusing - Phasing

achieved by delaying the pulse to the crystals


involves superimposition (algebraic summation)
of US waves



are pulsed in an outer to inner method, mimicking the
effect of a focusing lens
accomplished by offsetting the firing of crystals by
tiny time delay (phasing the beam)
varying the time between pulses changes the
focal distance
shorter delay between pulses = shorter focal
distance . improved spatial resolution
Electronic Transmission Focusing - Phasing


Allows the operator to control location
& & of focus (foci) in the image
Permits multiple focal zones on one image


unit sends out a pulse focused at a specified distance,
waits for the returning echoes & without moving to the
next scan line, sends out another pulse at a different
focal length. This is repeated for each focal zone
required. All the scan lines are combined to form one
dynamically focused scan line.
Frame rate is slowed down due to the extra time
required to process additional information
Beam Steering




used to sweep beams over an area
accomplished by delaying the electronic
pulse to each crystal causing the wave
fronts to be steered at various angles by
the wave interference phenomenon
US system alters the electronic pattern for
excitation of crystals
controlled by the operator
Steering, Focusing & Aperture




Returning echo information is delayed for proper
summation of the echo information
Time delays perform dynamic receive focusing to
process returning echoes & optimize image quality
When the transducer receives the returning echo, the
elements can be timed to be sensitive to listening at a
particular depth (range equation), as the focus is
constantly changed so to can be the reception of the
returning echoes. This is known as dynamic focusing.
Focus continues to change during echo reception, the
aperture increases to maintain a constant focal width, a
process called dynamic aperture

Multi-element transducers allow for
multiple focal distances to be possible
from one transducer


Mechanical focal lenses are used to reduce
the slice thickness of the beam
Slice thickness (elevational resolution) of the
beam varies with distance from the transducer
& cannot be varied by the operator
Apodization



transmit & receive technique using
different excitation voltage pulses across
aperture of segmented linear array to
reduce intensity of grating & side lobes
voltages are maximum at the center &
lower toward boundary of the beam at
transmission
changes in gain are applied to each crystal
of segment during reception
Subdicing


Division of normal crystal element into
many smaller sub-elements that are wired
together to form original size element & to
act as single crystal element
Reduces grating lobes
Dynamic aperture


Size of the transducer surface involved in
producing US beam & detecting echoes
Used to minimize beam width variations

keeps lateral resolution nearly constant over
entire image region
Aperture

Size can be controlled by varying the # of
active elements



bigger aperture - beam focus at greater depth
smaller aperture - beam focus closer to
transducer
Fixed aperture size - effective beam width
during transmission & reception varies
with depth
Transducer Care & Maintenance






Follow the care, maintenance, & sterilization
procedures recommended by the manufacturer
Routinely check for problems - tear in cable
covering, loose scanhead, malfunctioning crystals,
etc.
Do not use heat sterilization (autoclave)
Follow manufacturer’s recommended cleaning
agents so as to not void the warranty & swell the
probes membranes
Do not drop, bounce, or bang the scan head -it
will damage crystals
Do not run over or stand on the transducer cable
- it will damage wires
Arrangement
Display Shape
Beam Scanning
Method
Beam Focusing
Method
Mechanical oscillating
single crystal
Sector
Mechanical
Fixed
(conventional)
Mechanical rotating
multiple crystals
Curved top
sector
Mechanical
Fixed
(conventional)
Sequenced linear arrays
Rectangular
Sequencing
(electronic)
Conventional
Phased linear arrays
Rectangular
Sequencing
(electronic)
Phasing
Sequenced curved
(convex) linear
arrays
Curved top
sector
Sequencing
(electronic)
Conventional
Phased linear curved
(convex) arrays
Curved top
sector
Sequencing
(electronic)
Phasing
Phased arrays
Sector
Sequencing
(electronic) and
Phasing
Phasing
Vector Array
Trapezoidal or
Phasing
flat top sector
Phasing
Annular arrays
Sector
Phasing
Mechanical