Transducers and Beams Flashcards
Aperture
size of the source
Apodization
technical term for changing the shape of an electrical signal
Array
- an ordered arrangement
- the active elements are arranged in an array in the transducer
Axial
- or anterior to posterior is one dimension
- relating to an axis
- along the axis of the ultrasound beam
Axial Resolution
- The minimum distance 2 structures are separated from front to back or anterior to posterior, and still be distinguished as separate by the ultrasound machine
- along the axis of the ultrasound beam
- Perpendicular to scan plane width
- Determines section thickness artifact
Beam
in pulsed ultrasound, a description of the width of the pulse as it travels away from the transducer
Composite
- man made
- made up of various parts or elements
Convex Array
crystals are arranged in an arc
Crystal
main component of the transducer
Curie point
- temperature at which the crystals must not be heated above
- if heated above the Curie point they will loose their piezoelectric properties
Damping
- shortens SPL and pulse duration
- improves image quality
- compare to covering a bell with your hand as it is ringing
Detail/Spatial Resolution
the machines ability to see and differentiate structures and represent them as anatomically correct on the image
Dynamic Focusing
- improves accuracy of image
- causes the focus of the beam to become narrower
Element
-component used in the transducer (natural/man made) that vibrates and in turn transfers the sound wave to create the image
Elevational resolution
Perpendicular to the depth and beam scan direction
Far Zone/ Fraunhofer Zone
- region that lies beyond the distance of one near zone length
- place where the beam begins to diverge
Focal length
the distance between the center of a lens or curved mirror and its focus
Focal Region
the area of focus
Focal zone
area of highest, most uniform beam intensity
Focus
- the center of interest or activity
- the anatomy of interest should lie in the focus
Grating lobes
- a result of substancial acoustic energy directed outward, but not along the main axis of the sound beam
- most common with linear array transducer
Lateral
or side to side is a second dimension
Lateral/transverse resolution
- min distance that 2 structures can be separated and still show 2 separate echos on the screen
- perpendicular to beam path
Lead Zirconate Titanate (PZT) or barium
element in transdcuer
Lens
a piece of glass or other transparent substance with curved sides for concentrating or dispersing light rays
Linear
arranged in or extending along a straight or nearly straight line
Linear array
- produce sound waves parrallel to each other and produces a rectangular image
- elements arranged in a line
Linear phased array
elements are still arranged in a line but the array is very small
Linear sequenced array
- Multiple elements arranged in a line
- Elements are fired in sequence
- Image consists of parallel scan lines
- Rectangular image shape
- Conventional focusing
- NO Beam Steering
Matching Layer
- reduces reflections at transducer
- tissue interface
- also called impedance matching layer
- usually 1/4 the wavelength of the US beam
Natural focus
- ultrasound beam from a flat aperture will get narrow and then spread out within and angle range
- The depth where beam is most narrow is the natural focus of the aperture.
Near zone
area between the transducer and the focus
Operating frequency
- also called resonant frequency
- transducer frequency depends on
1. the thickness of the crystal
2. speed of sound in the crystal
phased array
- also called linear phased, or electronic sector
- elements are still in a line but the array is very small
Phased linear array
- also called linear phased, or electronic sector
- elements are still in a line but the array is very small
Piezoelectricity
- when a mechanical force or pressure is applied to certain materials a voltage is created
Probe
device that converts one from of energy into another
Resolution
accuracy of an image
Resonance Frequency
- operating frequency of the transducer
- natural frequency of vibration determined by the physical parameters of the vibrating object
Sector
Produces a fan like image that is narrow near the transducer and increase in width with deeper penetration
Side lobes
Although the main ultrasound beam is central, multiple beams are projected out from the
transducer in a diverging manner (side lobes)
Transducer
device that converts one from of energy into another
Vector array
Combination of phased array electronics and linear sequential array probes to provide electronic steering and multiple focal zones
Vector
Size May be small Crystals 120-250 Image Trapezoid Steering Electronic Focusing Electronic
Damage Vertical line
signal dropout
Convex Sequential
Size Long / Curved Crystals 120-250 Image Blunted Sector Steering Electronic Focusing Electronic
Damage Vertical line
signal dropout
Linear Sequential
Size Long / Linear Crystals 120-250 Image Rectangle Steering Electronic Focusing Electronic Damage Vertical line signal dropout
Annular Phased
Size Small Crystals Circular / Bull’s eye Image Sector Steering Mechanical Focusing Electronic from multi focal zones
Damage Horizontal band
of signal dropout
Linear Phased
Size Small Crystals 100-300 Image Sector Steering Electronic Focusing Electronic Damage Bad Steering and focusing
