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46 Cards in this Set
- Front
- Back
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case? |
protects the internal components from damage and insulates the patient. from electrical shock |
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should we use a cracked transducer? why not? |
transducer with a cracked case due to the potential for electrical shock to the patient |
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wire? |
each active element in a transducer requires electrical connection so that the voltage from the system can excite the crystal thereby producing sound during transmission. *do not use a transducer with a frayed wire. |
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matching layer |
the matching layer has an impedance between those of the skin and active element to increase then percentage of transmitted US between the active elements and the skin. gels impedance is in between those of the matching layer and the skin to further increase the efficiency of sound transmission |
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thickness of matching layer |
the ML is one-quarter wavelength thick |
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impedances: |
PZT>ML>GEL>SKIN |
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damping element or backing material |
RULE: short pulses create better image. therefore a material is bonded to the active element to reduce its "ringing" -commonly made of epoxy resin impregnated with tungsten |
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imaging transducer characteristics |
-low sensitivity -wide bandwidth (broadband) |
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bandwidth |
is the range of frequencies between the highest and the lowest frequency emitted from the transducer -compared to the therapeutic transducers imaging transducers are wide bandwidth or broadband |
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synonyms |
the main frequency emitted by the transducer is called the center, resonant primary or natural frequency |
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quality factor |
a unitless number, representing the extent of damping. imaging transducers are low-Q transducers when compared to therapeutic transducer because imaging transducers use backing material |
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continuous wave transducers |
sounds waves frequency equals the frequency of the voltage applied to the PZT by the machines electronics |
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pulsed transducers |
the main or center frequency of sound from a pulsed transducer is determined by 2 characteristics of the crystal: 1. thickness 2. propagation speed of the piezoelectric material the propagtion speed for PZT is approximately 4-6 mm/us |
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pulsed transducers |
high frequency 1. thin crystal 2. fast PZT lower frequency 1. thick crystal 2. slow PZT |
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when a PZT crystal is half as thick the sounds frequency is |
twice as high |
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thin active elements |
create higher frequency sound (called resonant or natural frequency: think of a crystal glass) |
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faster active element |
(higher propagation speed) creates higher frequency sound |
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PZT crystal |
1/2 wavelength thick |
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ML matching layer |
1/4 wavelength thick |
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when a transducer is covered with a sterile cover with gel on the inside what must the transducer avoid touching in order to create an image? |
talcum powder |
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T or F if the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz the main or center frequency of the transducer is 6 mhz |
false |
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T or false if the pulse repetition frequency of a transducer is increased the frequency of the US produced by the transducer remains the same |
true |
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T or F the diameter of the active element of a transducer helps determine the frequency of the US produced by the transducer |
false |
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T or F if the frequency of the electrical excitation voltage of a continuous wave transducer is 6 MHz the main or center frequency of the transducer is 6 MH |
true |
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T or F two piezoelectric crystals are made from the same material. the thicker crystal will make a pulsed transducer with a higher frequency |
false |
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T or F for a pulsed wave transduce, if the PZT crystal thickness is doubled then the frequency of sound is halved |
false |
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T or F the normal propagation speed for piezoelectric material is approximately three to five times greater than soft tissue? |
true |
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T or F the acoustic impedance of the matching layer equals the acoustic impedance of skin |
false |
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T or F a broadband transducer is more characteristic than a narrow bandwidth for imaging transducer |
true |
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T or F a very high "Q" factor transducer is more common than low "Q" factor for diagnostic imaging |
false |
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the impedance of a transducer active element is 1900000 rayls and for the skin is 1400000 rayls what is an acceptable impedance for the matching layer |
1726000 rayls |
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which PZT crystal will make a pulsed wave transducer with the highest frequency |
5,000m/s 1.5mm diameter |
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T or F the damping material in a transducer acts to : -increases the sensitivity? |
false |
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T or F the damping material in a transducer acts to : -increase the pulse length? |
false |
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T of F the damping material in a transducer acts to: -decreases the pulse duration? |
true |
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T or F the damping material in a transducer acts to : improve the systems lateral resolution |
false |
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T or F the damping material in a transducer acts to -improve the systems longitudinal resolution |
true |
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T or F the damping material in a transducer acts to: narrows the bandwidth |
false |
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T or F the damping material in a transducer acts to : decrease the quality factor |
true |
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with a pulsed wave transducer, which of the following occurs if the PZT thickness is halved |
frequency is doubled |
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with a pulsed wave transducer which of the following occurs if the PZT thickness is doubled |
frequency is halved |
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which of the following does not fit with the others |
good lateral resolution |
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beam width rule: |
narrow beams create better image |
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are sound travels the width of the beam change |
starts out at exactly the same size as the transducer diameter or aperture |
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focus or focal point |
the location where the beam reaches its minimum diameter |
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focal depth |
the distance for the transducer face to the focus also called focal length or near zone length |
