Chapter 12 Two-Dimensional Imaging Flashcards
What transducer has the following characteristics:
- contains a single, circular, disc-shaped active element
- image shape is fan or sector-shaped
- crystal moves with motor
- mechanical steering
- fixed focusing
- damaged PZT = no image
Mechanical Transducers
Modern transducers are called ________ and contain multiple active elements.
Arrays
An array comprises a single slab of PZT cut into a collection of seperate pieces called _________.
elements
A combination of the active element, wire, and system electronics is called?
channel
Types of Array Transducers?
Linear
Annular
Convex
Active elements arranged in a straight line is what type of array transducer?
Linear
Elements arranged as circular rings with a common center is what type of array transducer?
Annular
Active elements arranged in a bowed or arched line. Also called curved, or curvilinear array transducer?
Convex
What transducer has the following characteristics:
- narrow rectangle elements
- 100 to 300 active elements on face
- fan or sector-shaped image created
- no moving parts
- steered and focused with phasing
- electronic focusing
- damaged PZT = steering or focusing is off
Linear Phased Array
What always means “adjustable” or “multi-focus”?
Phased Array
How many elements are excited in a phased array probe during a single sound pulse?
All elements
The sound beam is directed downward when the spike line is _____________.
horizontal
The sound beam is steered is the spike line has a ________.
slope
The time differences between many wavelets create a single unified sound beam is also called?
phase delays
__________ ________ is achieved electronically without any moving parts in the transducer.
Beam steering
The electronics within the ultrasound system that create electrical patterns is called?
beam former
When a spike pattern is a straight line, an __________ sound beam is created?
unfocused
What happens when the spike line is curved?
The sound beam is focused
To determine beam steering, draw a line from the far ______ to the far _____ spike. The direction of steering is ___________ to this line.
left to right
perpendicular
What happens when the spike curve is curved outward or in a D-shape?
Defocused sound beam, has no application in diagnostic imaging.
Slope = _________
Steering
Curvature = ___________
Transmit focusing
In multifocusing three beams are created, what will the pattern with the greatest curvature create, and the pattern with the least curve?
Greatest curvature = shallowest focus
Least curvature = deepest focus
As the transducer listens for reflections, what happens to the delay patterns during receive-focusing?
Change continuously
Can the sonographer control the dynamic receve focusing?
NO, the system does it automatically
With dynamic receive focusing, focusing may also occur during…?
Reception
How do you determine if the beam is focused?
if the spike line is curved
How do you determine if the beam is steered?
if the spike line has a slope
What transducer has the following characteristics:
- Disc-shaped elements
- multiple rings with common center
- Image shape is sector
- multiple transmit focal zones
- mechanical steering
- electronic focusing
- damaged PZT = portion of image lost horizontal
Annular Phased Arrays
What transducer has the following characteristics:
- large acoustic footprint
- rectangle elements
- 120 to 250 rectangular-shaped strips of PZT
- image shape is rectangle
- electronic steering
- electronic focusing
- damaged PZT = portion of image lost where crystal is out
Linear Sequential Array
With linear sequential arrays, Electronic transmit focusing is achieved with a _________ excitation pattern of the active element.
curved
___________ ____________ is achieved dynamically by introducing electrical delays in the signals returning from the transducer.
Receive focusing
Can linear sequential array transducers steer sound beams electronically?
Yes, creating a parallelogram shaped image instead of rectangle shape.
What transducer has the following characteristics:
- array has bowed or curved shape
- 120 to 250 rectangle pzt
- image shape is blunted sector
- some but not all crystals fired simultaneously
- focused electronically
- damaged PZT = one section of pzt out, same section of picture out
Convex, Curved, or Curvilinear Array transducers
What transducer has the following characteristics:
- rectangle shaped elements
- 120 to 250 pzt
- electronic steering and focusing
- image shape is trapezoidal
- damaged PZT = poor steering and focusing
Vector Arrays
A __________ array is a combination of linear sequential and linear phased array technologies.
Vector
Technology where sloped phase delay patterns can electronically steer the sound beams in different directions is called?
vector or virtual sector
What is the synonym for slice thickness?
Elevational Resolution
Elevational Resolution depends on?
Transducer style
Elevational Resolution is created by?
structures that lie above or beneath the image plane
What shape of active element creates the thinnest ultrasound slices and the best elevational resolution?
Disc-shaped crystals
What transducers have the best elevational resolution?
Mechanical and annular phased array
The elevational resolution is identical to the ________ ___________ with disc-shaped active elements.
lateral resolution
What determines elevational resolution is phased array, linear array, and convex array transducers?
These array probes have rectangular-shaped active elements placed side by side. With phasing, the beam is focused or narrowed only side to side in the imaging plane, but not above and below. This narrowing improves lateral resolution but does not affect slice thickness.
What newer types of transducers have improved slice thickness?
1 1/2-D Array transducers
What is 4-D?
Real time 3-D imaging
__________ creates an image from 3-D data acquired during the ultrasound exam. It provides an element of realism to the image.
Rendering
Single element transducers create what kind of lobes?
Side lobes
Side lobes are created more in the _____ field.
far
Side lobes ________ lateral resolution.
degrade
Grating lobes are created by?
Array transducers
Grating lobes are created in the?
Near and far field
Side lobes bring back ________ information
reflective
Grating lobes are undesirable because?
- degrade lateral resolution
- reduce image quality
- create artifacts
Modern transducers are designed to reduce the strength of side and grating lobes. How is this accomplished?
by a process called apodization, which is exciting crystals inner first and weakening the signal as it moves to the outer crystals
What is subdicing?
it reduces grating lobes by grouping the crystals.
A technique called _________ __________ can be used to make a sound beam narrow over a greater range of depths and thus optimize lateral resolution.
Dynamic aperture
When the ultrasound system changes the number of crystals along the face of the probe, that is being used to transmit pulses ans receive reflections, is called?
Variable Aperture, or dynamic aperture
