Aperture
The size of a source of ultrasound
Apodization
The non-linear excitation of crystal elements
Axial Resolution
The ability of the system to accurately display 2 objects very close together that are parallel to the beams main axis
Array
Collection of active Elements in a transducer
Axial
Along the axis of the beam
Beam
description of the width of a pulse as it travels away from the transducer
Composite
Acoustic impedance of composite piezoelectric elements is closer to that of soft tissue, so matching is easier and more efficient with these transducers
Convex array
Crystals arranged in an arc; sector shape format
Crystal
piezoelectric element or active element
Curie point
Temperature point at which transducer crystals lose their piezoelectric properties
Damping
- Placed behind the active element
- Reduces the “ringing” of the pulse
Detail resolution
Determined by the transducer
Dynamic focusing
focusing the beam by altering the electric stimulation of various transducer elements either singly or in groups
Element
A single piece of PZT has been cut into many small pieces
Elevational resolution
“Slice Thickness” Thickness of the sound beam
Far zone
“Fraunhofer Zone”
- The part of the beam after the focus
- Sound beam is Diverging
Focal length
distance from the transducer to the center of the focal region
Focal region
An area with multiple focal zones
Focal zone
Area surrounding the Focal point where the best image is achieved
Focus
Concentrates the sound energy into a narrower beam. The best image resolution is at the focus
Grating lobes
- “an artifact”
- From an Array Transducer (Multiple Elements)
- Weaker then the central beam
- Can produce extra echoes on an image if they hit a strong reflector
- A line of band of echoes in an anechoic structure
Lateral
Scan plane width or beam diameter
Lateral resolution
The ability of a system to accurately display 2 closely objects perpendicular to the beams main axis, also known as transverse resolution
Lead zirconate titanate
PZT (most often used in diagnostic US transducers)
Lens
Used to improve image resolution by reducing the beam width of the transducer
Linear
Arranged in or extending along a straight or nearly straight line
Linear array
“Sequential” or “Switched” array
Linear phased array
Linear sequenced with phased focal control
Linear sequenced array
Rectangular in shape with a fixed focus and no electrical steering
Matching layer
Reduces the Impedance differences between the transducer
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
- “Fresnel’s Zone”
- The area between the transducer and the focal point
- The part where the sound beam is converging
Operating frequency
Element thickness: the operating frequency of a transducer is such that thickness is equal to one half the wavelength in the transducer element material
Phased array
flat arrangement of elements typically smaller footprint than linear probe, which produces a sector field of view
Piezoelectricity
When voltage is applied to these materials, they change shape and vibrate
Probe
an instrument that is used especially for examining parts of the body
Resolution
Ability to image accurately
Resonance frequency
The operating frequency of a transducer, also known as the natural frequency
Sector
Curvilinear array transducers; The area between an arc and two radii of a circle
Side lobes
A line of band of echoes in an anechoic structure “an artifact”
Transducer
converts one form of energy to another
Vector array
Combination of phased array electronics and linear sequential array probes to provide electronic steering and multiple focal zones
Phased linear array
small surface area that touches skin (compact footprint, square shape about 1cm on each side); no moving parts and electronically steered
