10 2-D Imaging Flashcards
What are B-scans or B-modes?
2-D images
What does a scanhead contain?
1 disc-shaped, element (like a coin)
What is steering in mechanical scanning?
The active element is moved by a motor, oscillating crystal or mirror through a pathway
What is focusing in mechanical scanning?
Conventional or Fixed - curvature (internal) of the PZT or an acoustic lens (external) focuses the beam at a specific depth
What is the image shape of a mechanical transducer?
Fan or sector-shaped
Scan lines spread apart creating gaps at greater depths
What does a defective crystal cause in a mechanical transducer?
Destroys entire image
What is a transducer array?
A collection of active elements in a single transducer
What is an element of a transducer array?
The separate pieces of a single slab of a PZT
What is the channel of transducer array?
Combination of electronic circuitry, the wire and the element
What is a linear array of a transducer?
A collection of elements in a line
- Linear switched array
- Linear phased array
What is an annular array of a transducer?
A group of ringed elements with a common center
What is a convex, curved, or curvilinear array?
Elements arranged in an arc
- Convex switched (or sequential) array
- Convex phased array
What are the # and shape of the crystals in a linear switched array?
Large transducers with approx 200 rectangular-shaped elements
What creates a narrow directional beam?
Few elements (3-10), but not all, are fired at exactly the same time This improves lateral resolution
What type of steering occurs in linear switched arrays?
Steering = Pulses sent down parallel lines
The scan lines are parallel and remain equally spaced at all depths
None in linear switched arrays
What type of focusing occurs in linear switched arrays?
Focusing = Lens (external) or curved crystal (internal)
Fixed
What is the image shape of linear switched arrays?
Rectangular image shape, no wider than the transducer
What are linear phased arrays?
Adjustable focus or multi-focus
What are the # and shape of crystals in a linear phased array?
Approx 200 rectangular-shaped elements arranged in a line
What is the focusing and steering in a linear phased array?
Electronic
A collection of electric pulses delivered to all of the transducer’s elements in various patterns for each sound pulse
What is the image shape of a linear phased array?
Fan or sector-shaped
What is phasing?
Minuscule time delays (10 ns) between electronic pulses delivered to the individual array elements
What does a defective crystal cause in a linear phased array?
If one element malfunctions, the steering and focusing become erratic
What is the electronic slope?
Creates beam steering
What is the electronic curvature?
Creates beam transmit focusing
What is a beam former?
Creates the electronic patterns
Delays are approx 10 ns
What is dynamic receive focusing?
Phase delays during reception can be applied to the electrical signals from the transducer to the US system which provides focusing at many depths during reception
How are the crystals arranged in an annular phased array?
Concentric rings cut from the same circular slab of PZT - looks like a bull’s eye target
What is the shape of the crystals in an annular phased array?
Small # of ring-shaped elements
How are the crystals arranged in an annular phased array?
Selected focal zones, use inner crystals for shallow regions and outer crystals for deep regions
What is the image shape of an annular phased array?
Fan or sector-shaped
How is the focusing in an annular phased array?
Multi-focusing, provides electronic focusing in all planes at all depths
Provides optimal lateral resolution at all depths throughout the image
What is the steering in an annular phased array?
Mechanically
What occurs with a defective crystal of an annular phased array?
Horizontal (side-to-side) band of dropout
What does a convex or curved array do?
Piezoelectric crystals arranged in a curve to provide a natural sector image
What is the image shape of a convex array?
Blunted-sector, fan shaped image
What does a large convex or curved array large transducer provide?
Convex sequential arrays place a large acoustic footprint on the patient
What creates 3-D or 4-D images?
2-D arrays
What do 1 1/2-dimensional arrays allow?
Focusing in the plane of the image making a thinner slice which improves the elevational resolution
What are vector arrays?
Combination of linear sequential and linear phased array
What is the image shape of a vector array?
Trapezoidal - a sector with a flat top that does not come to a point
