oct 17 Flashcards
converts one form of energy to another
transducer
convert electric energy into ultrasound energy, and vice versa
ultrasound transducers
to press
piezo
electron, organic plant resin that was used in early studies of electricity
amber
results in the production of a pressure when an applied voltage deforms these materials.
piezoelectricity
used commonly as materials in the production of modern ultrasound transducer elements
lead zirconate titanate
ceramics often are combined with a nonpiezoelectric polymer to create materials called
piezo-composite
take the form of disks.
single-element transducers
contain numerous elements that have a rectanguar shape
linear array transducers
refers to the piece of piezoelectric material that converts electricity to ultrasound, and vice versa
transducer element aka piezoelectric element
Elements, with their associated case and damping and matching materials, are called
transducer assembly
probe
scan head
or
transducer
produces a two- or three-cycle ultrasound pulse
single-cycle driving voltage
typically 5 to 30 cycles, are used for Doppler techniques
loner-driving voltages
preferred, or natural, frequency of operation for the element
operating frequency (sometimes called resonance frequency)
Operating frequency is determined by the following:
- The propagation speed of the element material (ct).
- The thickness (th) of the transducer element
Typical diagnostic ultrasound elements are ___mm thick and have propagation speeds of ___ mm/μs
0.2 to 1 mm, 4 to 6 mm/μs
higher frequency
better detail resolution
lower frequency
degradation in resolution
quicker, more convenient, and more cost-effective than changing of transducers
push-button frequency switching
in which echoes of twice the frequency sent into the body are received to improve the image.
harmonic imaging
mixture of metal powder and a plastic or epoxy resin, is attached to the rear face of the transducer elements to reduce the number of cycles in each pulse
Damping (also called backing) material
equal to period multiplied by number of cycles in the pulse
pulse duration
reduces pulse duration and spatial pulse length and improves resolution
damping
- reduces the time that the bell rings after the tap
- also reduces the loudness of the ringing
rubber
reduces the ultrasound amplitude and thus decreases the efficiency and sensitivity (ability to detect weak echoes) of the system (an undesired effect)
damping material
composites and damping material ___ pulses and ____ resolution
shorten, improve
facilitate the passage of ultrasound across the transducer-skin boundary
matching layer and coupling media
applied to the skin before transducer contact. This eliminates the air layer and facilitates the passage of sound into and out of the tissue
coupling medium
- designed to enter the body via the vagina, rectum, esophagus, or a blood vessel (catheter mounted type)
- allow the transducer to be placed closer to the anatomy of interest, thus avoiding intervening tissues and reducing the sound transmission path length
invasive transducers
refers to the width of a pulse as it travels away from the transducer
beam
The width in the scan plane determines the ____, whereas the width perpendicular to the scan plane determines the extent of the section thickness artifact.
lateral resolution
- additional beams
- source of artifacts
side lobes
region extending from the element to a distance of one near zone length is called the
near zone, near field, or Fresnel zone
- determined by the size and operating frequency of the element
Near-zone length (NZL; also called nearfield length)
Near-zone length increases with increasing frequency or element size, which is also called
aperture
The region that lies beyond a distance of one near-zone length is called
far zone, far field, Fraunhofer zone
What is somewhat surprising but true is that even in the case of this flat, unfocused transducer element, there is some beam narrowing. This narrowing is sometimes called
natural focus
size of a source of ultrasound
aperture
distance from the transducer to the center of the focal region
focal length
distance between equal beam widths that are some multiple (e.g., ×2) of the minimum value (at the focus)
focal zonelength aka depth of field in photography
wave length decreases, frequency ____
increases
thinner elements yield? higher or lower frequency
higher
pulse duration is equal to
period multiplied by number of cycles in the pulse
increase in frequency or in aperture
______ the near-zone length
increases
At a sufficient distance from the transducer, an increase in frequency or transducer size can _____ the beam diameter
decrease
