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
