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57 Cards in this Set
- Front
- Back
At the starting point, how wide is the sound beam width?
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The sound beam's width is the same as the transducer diameter
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As the sound beam gets further from the transducer, what happens to it?
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The sound beam narrows, like a funnel
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After the sound beam narrows, what happens to its shape?
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The sound beam expands
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What is the location where the beam diameter is the narrowest called?
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Focus or Focal Point
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What is the region from the transducer to the focus called?
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Near Zone
(aka Fresnel Zone) |
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At the far end of the near zone, what is the diameter of the near zone?
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1/2 the diameter of the active element
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The distance from the transducer to the focus is called what?
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Focal Length
(aka Focal Depth or Near Zone Length) |
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The region starting at the focus and extending deeper is called what?
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Far Zone
(aka Fraunhoffer Zone) |
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When the beam is two near zone lengths from the transducer, how wide is it?
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The beam is as wide as the active element again
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What happens to the sound beam width beyond two near zone lengths from the transducer?
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The beam widens beyond the width of the active element, and continues expanding
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The region around the focus where the beam is relatively narrow is called what?
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Focal Zone
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Why is the focal zone important to sonographers?
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Reflections arising from the focal zone create images of superior detail, compared to other depths
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What marks the end of the near zone?
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Focus
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At what point does the sound beam first begin to widen?
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Focus
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The focal zone is found where?
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Half in the near zone
Half in the far zone |
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The distance from the transducer to the focus is called what?
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Focal Depth
(aka Focal Length or Near Zone Length) |
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Is focal depth adjustable by sonographers on most modern ultrasound systems? If so, what is this called?
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Yes. Adjustable focus systems are called Phased Array
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For a fixed-focus transducer, what two characteristics determine the focal depth?
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1. Transducer Diameter
2. Sound Frequency |
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What is the relationship between transducer diameter and focal depth?
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Directly Related
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What is the relationship between frequency and focal depth?
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Directly Related
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High frequency transducers are used to image superficial, or shallow structures. How can this be when a high frequency beam will produce a deep focus (direct relationship)?
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Transducer manufacturers overcome this by making exceptionally small diameter crystals for high frequency transducers in order to locate the focus shallower for superior images
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The gradual spread of the sound beam beyond the focus is called what?
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Beam Divergence
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What two characteristics of a transducer determine beam divergence?
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1. Transducer Diameter
2. Sound Frequency |
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What is the relationship between crystal diameter and beam divergence?
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Inversely Related
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(Smaller|Larger) crystals produce beams that spread out (more|less) in the far field
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Small|more
Larger|less |
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Since larger diameter crystals create sound beams that diverge less in the far field, what would be improved in the far field?
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Lateral Resolution
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What is the relationship between frequency and beam divergence?
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Inversely Related
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Since high frequency sound beams diverge less in the far field, what would be improved in the far field?
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Lateral Resolution
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Less divergence involves what two characteristics?
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1. Larger Diameter (PZT)
2. Higher Frequency |
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More divergence involves what two characteristics?
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1. Smaller Diameter (PZT)
2. Lower Frequency |
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Shallow focus involves what two factors?
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1. Smaller Diameter (PZT)
2. Lower Frequency |
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Deep focus involves what two characteristics?
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1. Larger Diameter (PZT)
2. Higher Frequency |
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Very small pieces of PZT are called what?
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Huygens' Sources
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Very small pieces of PZT create sound waves in the shape of a "V" called what?
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Spherical Waves
Diffraction Patterns Huygens' Wavelets |
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This explains the shape of an imaging transducer's beam based upon in-phase and out-of-phase wavelets interfering with each other
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Huygens' Principle
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Accuracy in imaging is called what?
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Resolution
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The ability to distinctly identify two structures that are very close together when the structures are side-by-side, or perpendicular to the beam's main axis
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Lateral Resolution
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This answers the question: What is the minimum distance that two structures, positioned side-by-side, can be apart and still produce two distinct echoes on an ultrasound image?
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Lateral Resolution
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LATERAL RESOLUTION: units?
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Distance (mm, cm, etc)
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LATERAL RESOLUTION: determined by?
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Width of the sound beam
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How does a sonographer improve image resolution?
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Adjust depth; beam diameter varies with depth & a narrower beam has better resolution
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Synonyms for Lateral Resolution?
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Lateral
Angular Transverse Azimuthal |
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Which type of resolution is superior in clinical imaging systems: lateral or axial resolution?
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Axial Resolution because pulses are shorter than they are wide
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When two reflectors are closer side-by-side than the beam width, what will be observed in the image?
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One reflector, instead of two (suboptimal lateral resolution)
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What are the advantages of using a high frequency transducer?
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Axial resolution is improved due to its shorter pulses.
Lateral resolution is improved due to its pulses diverging less in the far field |
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What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with a lens?
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External Focusing
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What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with a curved active element?
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Internal Focusing
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What is it called when we improve lateral resolution by concentrating the sound energy into a narrower beam with the ultrasound system's electronics?
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Phased Array Focusing
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Which focusing technique(s) can be used with single element transducers? array transducers?
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Single Element Transducers = External & Internal Focusing
Array Transducers = Phased Array Focusing |
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External & internal focusing techniques are both called what?
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Fixed Focusing
Conventional Focusing Mechanical Focusing |
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What is a limitation to fixed focusing?
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Focal depth and the extent of focusing cannot be changed
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What four things happen to a beam when it is focused?
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1. Beam diameter in near field and focal zone is reduced
2. Focal depth is shallower 3. Beam diameter in the far zone increases 4. Focal zone is smaller |
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Continuous Wave Frequency: determined by?
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Electrical frequency from ultrasound system
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Pulsed Wave Frequency: determined by?
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1. PZT thickness
2. Speed of sound through PZT |
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Focal Length: determined by?
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1. PZT diameter
2. Sound Frequency |
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Beam Divergence: determined by?
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1. PZT diameter
2. Sound Frequency |
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Lateral Resolution: determined by?
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Beam Width
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