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Phys 254 > Module 5: Real Time Considerations > Flashcards

Module 5: Real Time Considerations Flashcards

1
Q

Real time scanning create an image that consists of what?

A

Multiple frames per second and each frame is made up of multiple scan lines

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2
Q

During real time consideration each scan line must wait for what?

A

All echoes to be received from the selected depth prior to the next pulse being sent out

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3
Q

What is the limitation for depth for real time scanning?

A

The limitation is the depth through a greater number of focal zones will increase the time it takes for each frame to be produced also

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4
Q

What is frame rate?

A

The number of times the sweep of sound is produced by the transducer (frames per second)

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5
Q

What is frame rate related to?

A

Temporal resolution in that if the frame rate increases then so does temporal resolution

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6
Q

Good temporal resolution gives use the ability to do what?

A

Image moving structures, overcome motion artifacts and surgery quickly

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7
Q

The human eye is capable of detecting flicker at what?

A

15-20 fps

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8
Q

Frame rates in imaging are what?

A

~30-60 fps and include ~120 lines

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9
Q

The factors affecting frame rate are what? 4

A
  1. Depth of field
  2. Sector angle
  3. Number of lines
  4. Number of focal zones
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10
Q

What is the formula for Frame rate?

A
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11
Q

FR = ((77,000)/(LPF x depth x # of foci))

Can also be called what?

A

Range ambiguity equation

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12
Q

The time to produce an image or 1 frame is what?

A

LPF x 13microseconds x depth(cm)

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13
Q

The frame rate is the reciprocal of the time to produce an image therefore what formulas can we see?

A
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14
Q

What is scan line density?

A

The number of lines per degree of number of lines per centimetre

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15
Q

What is the importance of line density ?

A

~1 degree is needed for appropriate resolution

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16
Q

Too low density needs what?

A

More interpolation and if its too high then overwriting will occur

17
Q

Aside from the axial, lateral and elevational resolution we need to consider scan lines as another aspect of what?

A

Spatial resolution

18
Q

Things that effect the scan line density have an impact on the details of what? 3

A

The images we see such as
1. # of scan lines
2. Number of focal zones
3. Size of the sector

19
Q

What is cine loop?

A

When the system stores numerous frames into the memory (~10-60 fps) that can be reviewed after freezing

20
Q

What does the machine need to run Cine loop?

A

Large memory capcity

21
Q

What is the advantage of a large capacity?

A

It can improve the efficiency of seeing tiny structures missed during the real time interrogation like valve motion in the heart during cine loop

22
Q

What is freeze frames ability?

A

The continuous display of a single frame in the memory on the monitor

23
Q

How is freeze frame accomplished?

A

The same image is read over and over and the raster display continually writes the image onto the display

24
Q

What is a CRT?

A

A CRT is still refreshing 30 frames per second even though the images is frozen

25
Q

What are side lobes?

A

Secondary projections of ultrasound energy that radiates away from the main beam

26
Q

Side lobes are limited to what?

A

Single disc mechanical probes

27
Q

What is a key contributor for side lobes?

A

Radial mode vibration

28
Q

What can side lobes do? Why?

A
  1. Falsely place reflectors in the image as if they came from the main beam
  2. The machine assumes that all reflections must come from the center
29
Q

To compensate for side lobe artifacts, what do we use?

A

Insulating ring is added to the element to suppress the radial mode vibration

30
Q

What are grating lobes?

A

Like side lobes but are specific to array probes

31
Q

What is the assumption made by the machine with the result being an artifact?

A

The same as side lobes

32
Q

The vibration of the crystals is again responsible for what during grating lobes?

A

Crosstalk

33
Q

What do we use to reduce grating lobes?

A

Apodization

34
Q

What is sub dicing?

A
  1. Another means of eliminating the impact of grating lobes
  2. Each elements is divided into smaller pieces or sub elements that will act as one crystal
35
Q

For grating lobes if the sub elements are cut to a dimension less than a wavelength than what happens?

A

Grating lobes will project at 90 degrees or greater to the main beam

36
Q

What does channels refer to?

A

The number of elements in the array?

37
Q

Systems usually have how many channels?

A

48, 64, 128

38
Q

More channels means what in terms of beam characteristics?

A

More precise control

39
Q

What’s the moderate range for frame rate?

A

5-40

Phys 254 (19 decks)

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