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70 Cards in this Set

  • Front
  • Back
what is housing?
surround structures except the connector and is usually constructed of plastic. It holds the transucer together and provides something for sonographers to grip.
connector
electronic link btw transducer and ultrasound unit.
tuning wires
allow the maunfacture to fine tune the transducer so that the crystal more closely matches the electronics of the scanner. This allows for optimal imaging.
electrical wires
electrical signal must be transmitted from connector through tuning wires and then to the crystal. that's the job of the electrical wires.
crystal, transducer, element
generates the ultrasound wave which will be transmitted to the patient.
-electrical energy is converted into mechanical energy and visa versa.
what determines the crystal thickness?
crystal thickness is about 1/2 the wavelength of sound emitted by the crystal.
what are some naturally occuring peizoelectric materials?
quartz
lithium sulphate
rochelle salts
tourmaline
what are some synthetic peizoelectric materials?
PZT(most common)
barium lead titanate
lead metianobate
PVF
what material decreases or eliminates the need for matching layers? why?
PVF(polyvinylidene flouride)-it has an acoustic impedence closer to that of human soft tissue.
what are piezoelectric materials?
material that produce a voltage when strain or pressure is applied to them.
what is the reverse peizoelectric effect?
when a voltage is applied to peizoelectric material, it is deformed.
What material contain dipoles?
ferroelectric material
T/F all piezoelectric material is ferroelectric
true
what are ferroelectric materials?
materials that are able to retain their dipole arrangementa after electrical field is removed.
Why are transducers not autoclaved?
the process will excede the curie temperature causing the crystal to lose it's piezoelectric qualities
what is a composite element? what are it's qualities?
when piezoelectric materials are combined with other materials. THis results in a lower impedence, and improved sensitivity, bandwidth, and resolution
Insulators
crystal has a tendancy to vibrate up and down, so the insulating rings damp this vibration.
damping(backing)material
This dampens or reduces the number of cycles of the ultrasound wave.
WHat is mechanical damping?
the energy that is lost by reducing the number of cycles absorbed by the damping material.
Electrical shield.
-lines the inside of the housing
-provides a shield from external electrical interference(ie. radio frequencies,etc) This increases the signal to noise ratio.
Matching layer; what is the optimal thickness of a matching layer?
minimizes the acoustic impedence difference at the transducer patient interface. The optimal thickness of the matching layer is 1/4 of the wavelength. Use of a matching layer causes the beam to have a wider bandwidth which allows better matching of the crystal to electronics of the ultrasound system.
What is the main bang?
in the old days, this was the result of a large acoustic impedence difference at the transducer patient interface.
What are the 2 ways in which ultrasound crystals can be activated?
-shock excited mode-single burst of non-alternating voltage
-burst excited mode-crystals are activated by one or two cycles of an alternating current. This allows the sonographer to select the frequency operated by the transducer.
what is bandwidth?
range at which the transducer frequencies operate
what is the formula to determine the frequency at which a crystal will vibrate?
propegation speed/2xthickness(mm)
as the thickness of a crystal decreases, what happens to the transducer frequency?
it increases
what is bandwith? What is a synonymn for it?
the difference btw the highest and lowest frequency emitted. Synonymn is transducer pass band
how does SPL affect the bandwidth?
the shorter the SPL, the wider the bandwidth.
what are some advantages of wide bandwidth tranducers?
-are necessary for multihertz transducers
-impove sensitivity
-improve image quality
-better axial resolution
-crystal more easily matched to electronics
-low frequencies in the beam can be controlled to decrease beam divergnece in the far field.
what happens to the bandwidth as spacial pulse length increases?
bandwidth decreases.
what are 1/4 and 1/2-power bandwidths?
pass bands that eliminate the weaker 1/2 or 1/4 of the frequencies.
which is narrower, a half power bandwidth, or a quarter power bandwidth?
a half hower.
what is fractional bandwidth, what is the formula?
fractional bandwidth=bandwidth/frequency
what(with regards to the fractional bandwidth) is considered a narrow bandwidth?
bandwidth is considered narrow if the fractional bandwidth is less than or equal to 15 percent.
what is Q factor?
a measure of how efficiently the transducer changes electrical voltage to a sound wave. Also indicates how good of a transmitter a crystal is.
What are the formulas for Q factor?
Q=operating frequency/bandidth
Q=energy stored per cycle/energy lost per cycle
Q=1/fractional bandwidth.
T/F Q factor is approximately equal to the number of cycles in a pulse
True
as the Q increases, what happens to the bandwidth?
it decreases
as the Q increases, what happens to axial resolution?
it degrades
what 3 things happen as the SPL becomes shorter?
-axial resolution improves
-bandwidth increases
-Q factor will decrease
what is transmission co-efficient?
fraction of electrical energy converted into acoustic energy.
reception co-efficient?
fraction of returning energy converted into electrical energy
electromechanical coupling co-efficient
how efficiently the transducer converts electrical stimuli into ultrasound energy and recieved ultrasound energy back into electrical energy.
dielectric constant
characterises mechanical and electrical properties of a crystal. Describes movement of a crystal when voltage is applied ot it,and to voltage induced when a strain is applied to it.
acoustic impedence
a measure of the resistance of a medium to the transmission of sound.
state 3 synonymns for transducer frequency?
preffered, operating, resonate, central
what are the consequences of not including backing material in transducers?
decreased axial resolution, decreased sensitivity
why is damping material not inculded in trasducers used specifically for continuous wave applications.
because damping material causes SPL to be shorter, but since continuous waves don't have SPL, it doesn't matter. Also, using damping material causes a loss in energy, so it is better not to use it.
why is the inculsion of backing material considered mechanical damping?
because the pulse is dampened by physical means
what are the implications of changing the thickness of the crystal?
change the central frequency of the beam
what is pass band?
bandwidth
why are wide band transducers typically preferred over narrower band transducers
because they improve axial resolution, increase sensitivity, multihertzing, increased image quality, crystal more easily matched to system
a transducer which is .22 mm thick, will produce what frequency?
element thickness is half the wavelength, so a transducer with .22 with produce a wavelength of .44. This goes into the c=f/wavelength to get 3.5 mHZ
For a given frequency, what will happen to the fractional bandwidth as the bandwith increases?
decreases
what would happen to the ultrasound image is hte matching layers are removed?
overall image quality would degrade. Decreased axial resolution, decreased sensitivity, decreased penetrating ability
how thick is the typical matching layer?
1/4 wavelength
why are composite crystal the rule rather than the exeption?
composities produce a beam with lower impedence, wider bandwidth, greater sensitivity, and better axial resolution
why should transducer elements never be subjected to a temperature which exceeds the curie temperature?
loss of piezoelectric qualities
what measures can ve taken to improve sensitivity?
adding matching layers, increased output or gain
what benefit does the presence of the electrical field bestow?
increased image quality, prevent radio frequencies from reaching the transducer, produce artifacts
what would be the consequence of not having amatching layer attached to the face of the crystal?
the acoustic impedence remains high which causes a large reflection of energy
the lack of which transducer part could result in unacceptable side lobes.
insulator
for a given transducer material, what happens to the frequency when crystal thickness is reduced by half?
frequency is doubled
as the transducer increases, what happens to the bandwidth?
it becomes narrower
what is the advantage of a 2-d transducer over a 1.5D transducer?
can focus in more dimentions. THere is an increase n the # of rows increasing the possiblity for timing delays.
what are vaxels?
3D pixels
what are some free hand scanning methods with sensors?
-articulated arm-gantry system
-magnetic field-transmitter transmitts several different magnetic fields so the machine can tell the orientation of the transducer
-acoustic ranging-have recievers in the ceiling
-imaged base corrilation-camera looks for similar traits in am=n imge and it matches them up
what are grating lobes?
beams of energy not in much of the ultrasound beam-angle depends on wavelength and element spaceing
what is subdicing?
choping a crystal into 4
which part of the transducer is responsible for improving the signal to noise ratio?
electrical field