Term
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Definition
| A 2-dimensional image is built up by firing a beam vertically, waiting for the return echoes, maintaining the information and then firing a new line from a neighboring line in a sequence of B-mode lines. |
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| 2-D images are referred to as |
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Definition
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| Ultrasound travels only in a |
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Definition
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| Sound beams must be narrow to optimize |
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Definition
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Term
Mechanical Transducer:
The image created by a mechanical transducer is |
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Definition
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Term
Mechanical Transducer:
The minimum number of active elements in a mechanical transducer |
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Definition
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Term
Mechanical Transducer:
Element in a mechanical transducer is shaped like a |
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Definition
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Term
Mechanical Transducer:
Beam steering in a mechanical transducer is |
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Definition
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Term
| Mechanical Transducer Image Shape |
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Definition
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Term
| Mechanical Transducer Focusing |
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Definition
| Conventional or fixed: If you want to change focus you have to change scan heads |
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Term
| Mechanical Transducer Focusing |
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Definition
| Through internal or external acoustic lenses that focuses the beam at a specific depth. |
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Term
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Definition
| a collection of active elements in a single transducer |
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Term
Transducer Arrays:
Element |
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Definition
| a single slab pf PZT cut into seperate pieces called and element |
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Term
Transducer Arrays:
Modern transducers called arrays, contain |
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Definition
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Term
Transducer Arrays:
Each active element is connected to it's own electronic circuitry called |
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Definition
| channels, therefore it can excite single or groups of elements in various ways during transmission |
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Term
Transducer Arrays:
Linear Array |
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Definition
| a collection of elements in a line |
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Term
Transducer Arrays:
Two Types of Linear Arrays |
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Definition
1. Linear switched ( or sequential) array
2. Linear phased array |
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Term
Transducer Arrays:
Channel |
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Definition
| combination of electronic circuitry, the wire and the element |
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Term
Transducer Arrays:
Annular Array |
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Definition
| a group of ringed elements (bull's eye) with a common center |
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Term
Transducer Arrays:
Convex, Curved, or curvilinear array |
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Definition
elements arranged in an arc
There are two types
1. Convex switched array
2.Convex phased array |
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Term
Linear Switched or Sequential Arrays:
*Crystals # and shape |
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Definition
| large transducers with approximately 200 rectangular-shaped elements arranged in a line. |
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Term
| Linear Switched or Sequential Arrays: |
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Definition
| A few elements (5-10) but not all, are fired at exactly the same time. This improves lateral resolution |
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Term
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Definition
| gives a large probe surface (footprint) and near field, and a narrow sector |
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Term
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Definition
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Term
| Can linear array transducers steer sound beams electronically? |
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Definition
| Yes - this form of beam creates parallelogram shaped images rather than rectangular images |
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Term
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Definition
| adjustable focus or multi-focus |
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Term
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Definition
| crystals - approximately 200 rectangular shaped elements |
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Term
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Definition
| remember phased arrays always means adjustable or multi-focus |
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Term
Phased Arrays:
Crystals, Steering and Focusing |
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Definition
| - a collection of electric pulses is delivered to all fo the transducer's elements in various patterns. Thus, focusing and steering are electronic. |
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Term
Phased Arrays:
Image Shape |
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Definition
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Term
Phased Arrays:
Defective Crystal |
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Definition
| If one element malfunctions, the steering and focusing become erratic |
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Term
| Beam Steering of Linear Phased Arrays: |
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Definition
| With no time delay there is no beam steering or focusing |
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Term
| Beam Steering of Linear Phased Arrays: |
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Definition
| The slope of the electrical spike line determines the direction of propagation of the sound beam |
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Term
| Beam Steering of Linear Phased Arrays: |
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Definition
| The sound beam is directed straight ahead when the spike line is vertical. |
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Term
| Beam Steering of Linear Phased Arrays: |
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Definition
| The sound beam is steered if the spike line has slope! |
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Term
The sound beam is steered if the spike line has slope!
Electronic Curvature = |
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Definition
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Term
The sound beam is steered if the spike line has slope!
Electronic slope = |
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Definition
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Term
Beam Steering of Linear Phased Arrays:
The beam former of the system: |
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Definition
| creates these electronic patterns at delays of approximately 10 nanoseconds |
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Term
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Definition
| Similarly, time delays during reception can be applied to the electrical signals from the transducer to the US system |
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Term
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Definition
| allows focusing at many depths. This reception zone focusing relates to the depth of the returning echoes and optimizes image quality |
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Term
Annular Phased Arrays:
* Crystals - |
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Definition
| Concentric rings cut from the same circular slab of PZT. The array looks like a bull's eye target. Small number of crystals. |
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Term
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Definition
| Selected focal zones use inner crystals for shallow regions and outer crystals for deep regions |
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Term
Annular Phased Arrays:
*Image Shape - |
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Definition
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Term
Annular Phased Arrays:
*Focusing |
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Definition
| Electronic multi-focusing planes |
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Term
Annular Phased Arrays:
*Steering |
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Definition
| Only one that is performed mechanically |
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Term
Annular Phased Arrays:
*Defective Crystals |
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Definition
| Causes a horizontal (side to side) |
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Term
Annular Phased Arrays:
Phased or Segmental |
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Definition
| adds phasing to add electronic focus capabilities |
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Term
Annular Phased Arrays:
Phased or Segmental |
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Definition
| multiple focal zones require multiple rows of elements |
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Term
Annular Phased Arrays:
Phased or Segmental |
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Definition
| allows steering of Doppler elements |
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Term
Convex or Curved Arrays:
*Crystals |
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Definition
| 120-250 rectangular shaped crystals |
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Term
Convex or Curved Arrays:
*Curved shape: |
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Definition
| so it provides a natural sector shape (blunted-sector) |
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Term
Convex or Curved Arrays:
Similar to linear arrays |
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Definition
| convex sequenced array - behave same as linear sequenced arrays |
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Term
Convex or Curved Arrays:
Image Shape |
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Definition
| Blunted-sector, fan shaped image |
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Term
Convex or Curved Arrays:
Large Transducer |
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Definition
| Convex sequential arrays place a large acoustic footprint on the patient. |
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Term
Convex or Curved Arrays:
*Acoustic Footpring |
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Definition
| describes the area of contact between the transducer and the skin |
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Term
Convex or Curved Arrays:
*small transducers |
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Definition
are typically a convex phased array transducer
* so you can have both foot print type transducers |
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Term
Convex or Curved Arrays:
*Large Transducer |
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Definition
| makes blunted sector fan shaped image |
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Term
Convex or Curved Arrays:
*Small Transducer |
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Definition
| will have a small foot print but still be phased array |
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Term
Convex or Curved Arrays:
*Beam Focusing is |
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Definition
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Term
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Definition
| a combination of linear sequential and linear phased arrays |
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Term
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Definition
| The beam is steered on the edges like a phased array, but goes straight down in the middle like a linear array. This produces a beam with a flat top, and fan shaped sides. |
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Term
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Definition
| This technology extends the field of view on linear transducers, providing the opportunity to see more relational anatomy around structures, and in some cases the ability to complete measurements on one structer that would not e possible with an standard linear array image format |
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Term
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Definition
| Used in high frequency transducers |
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Term
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Definition
| Example 12 MHz to do testicular scans |
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Term
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Definition
| Image is trapezoidal in shape |
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Term
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Definition
| The top of the vector's array is flat |
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Term
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Definition
| Get side & /or grating lobes |
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Term
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Definition
| Slice thickness artifacts |
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Term
Problems with Arrays:
*Side lobes |
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Definition
| present in all transducers (single or multiple crystals) |
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Term
Problems with Arrays:
*grating lobes |
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Definition
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Term
Problems with Arrays:
To decrease the effects of these problems |
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Definition
| the sensitivity of the peripheral elements is decreased - Apodization |
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Term
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Definition
| Sound beams created by single element transducers are hourglass shaped. However, additional areas of sound energy at depths equal to and greater than the focal zone extend outside of the main beam. These off axis beams are called side lobes |
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Term
Problems with Arrays:
*Side Lobes |
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Definition
| degrade lateral resolution |
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Term
Problems with Arrays:
*Side Lobes |
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Definition
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Term
Problems with Arrays:
Side Lobes |
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Definition
| These are created by mechanical or single crystal transducers |
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Term
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Definition
| Similar to side lobes but are created by array transducers. These are extra off axis sound beams that degrade lateral resolution |
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Term
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Definition
| Since lobes create artifacts, it is best to eliminate them. This can be done by Apodization |
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Term
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Definition
| Grating lobes can be eliminated by exciting the elements with different voltages. The elements closer to the center of the sound beam are excited with higher voltages, while the elements further away from the center are excited with lower voltages. |
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Term
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Definition
| This is accomplished by varying the number of elements use to receive the reflected signal. |
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Term
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Definition
| Echoes arising early ( from shallow structures) are received using only a few crystals from the array |
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Term
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Definition
| As the echoes return from deeper structures, the aperture is increased. More and more elements in the array are used to listen. This allows the beam to be as narrow as possible at all depth, and optimizes lateral resolution at all depths. |
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Term
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Definition
| A type of electronic focusing |
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Term
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Definition
| In order to keep the focal zone the same size at different depths (maintain the same beam width), the aperture or scanning window must increase as well |
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Term
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Definition
| As the returning sound beam strikes the transducer, size of the transducer surface that listens for echoes is varied |
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Term
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Definition
| Amplitude - a series of upward spikes |
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Term
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Definition
| As a sound pulse is emitted by the transducer, a dot moves at a constant speed across the system's display |
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Term
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Definition
| When a reflection returns to the transducer, it is processed and the moving dot is deflected upward on the screen |
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Term
Display Modes:
Three formats or modes of display |
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Definition
1. Amplitude Mode
2. Brightness Mode
3. Motion Mode |
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Term
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Definition
| The height of the upward deflection is proportional to the amplitude of the returning echo, thus the name amplitude mode |
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Term
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Definition
| The x axis represents reflector depth |
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Term
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Definition
| The y axis represents reflection amplitude |
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Term
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Definition
| accurate in determining the depth of reflectors. This mode is used in opthamology |
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Term
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Definition
| Now obsolete in medical imaging. Wave spikes are represented when a single beam passes through objects of different consistency and hardness. The distance between these spikes |
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Definition
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