Term
| What are the different types of resolutions? |
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Definition
- Spatial
> Axial
> Lateral
> Elevational (slice thickness)
- Temporal
- Grey Scale |
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Term
| What is axial resolution? |
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Definition
| The smallest distance between two objects along the axis of the beam that is distinguishable. |
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Term
| What are the other possible names for Axial resolution? |
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Definition
(LARD)
Longitudinal resolution
Axial resolution
Radial, Range resolution
Depth resolution |
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Term
| What is the minimum distance between two objects that can be resolved? |
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Definition
The minimum distance between two objects that can be resolved must be no smaller than 1/2 of the SPL. (So the minimum distance must be greater than 1/2 of the SPL)
LARD > 1/2 SPL |
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Term
| What should a technologist do to improve axial resolution in regards to SPL? |
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Definition
TO IMPROVE AXIAL RESOLUTION THEY SHOULD SHORTEN THE SPL:
- Smaller wavelength (higher frequency)
- Decrease crystal ringing -> Less cycles per pulse
> Backing Material
> Dynamic Damping |
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Term
| What is lateral resolution? |
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Definition
| The shortest distance between two objects that can be resolved PERPINDICULAR to the axis of the beam. |
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Term
| What are the possible names for lateral resolution? |
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Definition
(LATA)
- Lateral Resolution
- Azimuthal Resolution
- Transverse Resolution
- Angular Resolution |
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Term
| Reflectors positioned more than one beam width apart are seen as... |
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Definition
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Term
| Reflectors positioned less than the width of the beam are seen as... |
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Definition
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Term
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Definition
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Term
| The narrower the beam width the... |
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Definition
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Term
| An unfocused beam has a _____ beam. |
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Definition
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Term
| A focused beam has a ____ beam. |
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Definition
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Term
| Does an US beam have a uniform width? |
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Definition
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Term
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Definition
1. Beam Converges
- Near field
- Fresnel Zone
- Focal Length
2. Focal Zone
- Focal Point (In the middle of the focal zone, the narrowest part of the beam)
3. Beam Diverges
- Far field
- Fraunhofer zone |
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Term
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Definition
| An area in space that contains at least 4% of the max amplitude. |
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Term
| Explain Focal Point in full. |
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Definition
- Focal point is the narrowest part of the beam.
- The focal point is where you get the best LATA.
- The focal point is 1/2 the width of the crystal. |
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Term
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Definition
- The focal zone is the portion of the beam that surrounds the focus.
- Amplitude in the focal zone is within 1/2 of the max amplitude. |
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Term
| What is the Near field (Fresnel zone)? |
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Definition
| - The area where the beam converges. It is found between the face of the transducer and the focal point. |
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Term
Does depth of the near field (focal length) have good LATA?
What does it depend on? |
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Definition
- Yes, it has good LATA.
- It depends on the width of the crystal and it's frequency. |
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Term
| What is the far field (Fraunhofer zone)? |
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Definition
| The area where the beam diverges. It is found away from the focal point. |
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Term
What is LATA like in in the far field (Fraunhofer zone?
What affects the divergence? |
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Definition
- The LATA here is poor.
- Divergence of the far field decreases as the frequency and width of the crystal increases. |
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Term
| Summary of low frequency transducers |
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Definition
- Shallow focus
- LATA at focal point is not affected.
- Big divergence means poor LATA in the far field. |
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Term
| Summary of high frequency transudcers |
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Definition
- Deep focus
- LATA at the focal point is not affected.
- Divergence decreasing means a narrower beam = better LATA in the far field. |
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Term
| Summary of narrow crystal |
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Definition
- Shallow focus
- Better LATA at the focal point
- Big divergence in the far field = wider beam = worse LATA |
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Term
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Definition
- Deep focus.
- Poor LATA at the focal point.
- Less divergence = narrower beam = better LATA in the far field. |
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Term
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Definition
| Focusing allows the narrowing of the beam through either mechanical or electronic means. |
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Term
| Does focusing improve LATA? |
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Definition
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Term
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Definition
1: Focusing:
2: Fixed (Mechanical)
- Internal (Curved Mirror)
- External: -> Acoustic Lens -> Acoustic Mirror
3: Adjustable
- Aperture -> Electronic (Transmits) -> Dynamic (Receives) |
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Term
| How is good LATA at multiple depths achieved? |
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Definition
| - The same area gets scanned multiple times with various focal positions. |
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Term
| What is elevational (slice thickness) resolution? |
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Definition
| - The smallest distance between two objects that can be resolved perpendicular to the axis of the beam (z-axis). |
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Term
| Explain how dimensions (3D, 2D) play a role in elevational resolution. |
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Definition
- The actual beam is 3D.
- The displayed image on the screen is only 2D because the 3rd dimension is compressed on the image. |
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Term
| How could one improve elevational resolution? |
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Definition
| - To improve the elevational resolution one should focus the beam, and they do this by decreasing the thickness of the beam (similar to decreasing width of the beam for better LATA). |
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Term
| Are images on the screen echoes received from 1 scan line or multiple scan lines? |
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Definition
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Term
| What must be be done to get echoes from a broad area with good LATA? |
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Definition
- The machine must sweep the area (steer it).
- To get good LATA, the beam should be focused. |
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Term
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Definition
| A single image on the screen. |
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Term
| What is the max. number of frames displayed per second? |
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Definition
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Term
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Definition
| The frame rate is the number of images produced per second. |
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Term
| What is temporal resolution? |
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Definition
| - The ability to see changes in time. |
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Term
| What does frame rate represent? |
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Definition
| Temporal resolution; the HIGHER the frame rate, the better the temporal resolution. |
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Term
| How do you improve temporal resolution in 2D? |
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Definition
(Lovers Always Need Loving)
- Lower depth
- Avoid Multi-focusing
- Narrow Sector
- Lower Line Density |
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Term
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Definition
| The distance from the front face of the transducer to the first identifiable echo at the phantom/patient interface. |
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Term
| Define Axial Resolution and Lateral Resolution by the lab standards. |
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Definition
- Axial Resolution is the minimum reflector separation between two closely spaced objects positioned ALONG the propagation of the sound beam.
- Lateral Resolution is the minimum reflector separation between two closely spaced objects positioned PERPENDICULAR to the propagation of the sound beam. |
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