Chapter 12 Flashcards
Mechanical Transducer
Not in use today
Contains a single, circular, disc shaped element
image is sector (fan or pie) shaped
small footprint
Focusing was mechanical
Crystal damage lost entire image
Footprint
face of probe that comes into contact with the skin
a channel
Each element is connected by a wire to its own electronic circuitry
Arrays
contain multiple active elements
A single slab of PZT is cut into many pieces or elements
Array Transducers
Linear: Active elements are arranged in a straight line
Annular: Elements are arranged as circular rings of PZT
Convex, Curved or Curvilinear: Elements are arranged in a curved, bowed, or arched line
Linear Phased Array Transducer (cardiac sector probes)
Compact with small (~1 cm) rectangular footprint;
Elements are very thin
100-300 narrow rectangular elements
beam is focused electronically
phasing
All crystals are stimulated to create each beam
Linear Phased Array and Multi-focusing
To create an image with multiple foci at different depths, the system must send multiple sound beams down each scan line
Dynamic Receive Focusing
A more accurate image can be created when the ultrasound receiver introduces time delays to some of the electrical signals during reception
(performed automatically)
Annular Phased Array Transducer
Elements are rings of PZT
Mechanical steering
Small footprint
Fan or pie shaped
Electronic focusing
Horizontal band of dropout
Linear Sequential Array Transducer
Large footprint
rectangular image
Used in vascular imaging
120-250 strips of PZT
Electronic steering
vertical band of dropout
sequencing
Elements are stimulated in groups simultaneously to send the pulse straight ahead
Then the next group of crystals is stimulated to direct the next sound beam straight ahead
Convex, Curved, or Curvilinear Sequential Array Transducers
120-250 strips of PZT
used for Abdominal or OBGYn
Large footprint
beams steered electronically with sequencing
top of sector wide as footprint
electronically focused
vertical band of dropout
Vector Array Transducers
120-250 strips of PZT
medium footprint
beam steering electronically sequenced
electronic focusing
vertical band of dropout
trapezoid image
vascular and cardiac image
Image resolution
Shallow to deep = longitudinal resolution
Side to side = lateral resolution
Top to bottom (height) of the imaging plane = slice thickness/elevational resolution
Ranking of resolutions for disc probes from best to worst
longitudinal then lateral/elevational
Ranking for these 1D array probes
longitudinal/axial resolution is best, then lateral, then elevational
ranking with 1 1/2 probes
axial, lateral, then elevational
Three-Dimensional (volume) Imaging
Utilizes a 2D array (as many rows as columns)
Thousands of elements
Rendering
creates the displayed image from the volume of echo data (allows certain image planes to be accentuated or shadowed)
lobes
Extra off-axis sound beams can happen
Side Lobes
These off-axis sound beams found at depth equal to and past the focus of single disk element probes
Grating Lobes
Extra beams found along the length of the array transducers
Subdicing
reduces grating lobes
A crystal is divided or “scored” into smaller crystals
apodization
stronger electrical signals are used to excite the inner crystals, and progressively weaker electrical spikes excite the outer crystals
dynamic aperture probe
progressively recruits more outer elements as it images deeper accomplishing a narrow beam over a substantial range of depth
