# Test 3 Flashcards Preview

## Physics II > Test 3 > Flashcards

Flashcards in Test 3 Deck (84)
1
Q

What does the scan converter do?

A

It writes data to memory/pixel (“picture element”)

2
Q
A
3
Q
A
4
Q

What are two types of scan converters?

A
1. Analog→continuous
2. Digital→Discrete steps (with clock)
5
Q

What are some examples of a analog scan converter?

A
• Actual BP
• Tidal volume
• EKG
• Acutal body temperature
6
Q

What is the scan converter directly related to?

A

The nyquist limit

7
Q

What does the nyquist limit mean?

A

“speed limit”

It is the highest Doppler frequency or velocity that can be measured without the appearance of aliasing.

8
Q

Formula for nyquist limit is:

A

Nyquist limit (Hz)=PRF (Hz)/2

9
Q

What are two ways to avoid aliasing?

A
1. Raise the nyquist limit
2. Reduce the Doppler shift
10
Q

What happens when the sample volume is deep?

A

The PRF is low and the Nyquist limit is low.

• Velocity is sampled fewer times each second, and the system is unable to accurately measure high velocities.
• Deeper sample volumes have a lower pulse repetition frequency and create aliasing.
11
Q

What happens when the sample volume is shallow?

A

The PRF is high, velocity is sampled many times each second, and the Nyquist limit is high.

12
Q

Sampling always needs to be…..

A

greater or equal to 2x per cycle.

13
Q

What does the scan converter subsitute?

A

It substitutes high frequency for low frequency.

14
Q

How is digital format demonstrated?

A

It is demonstrated by bits and pixels.

15
Q

What is the basic storage device?

A

“bit”

16
Q

What are the 2 levels for a bit?

A

On & off/

(0 or 1)

17
Q

What does n equal?

A

n=#bits

18
Q

what does 2n equal?

A

The number of combinations.

19
Q

What does the scan converter convert from?

A

It converts from binary (base 2) to decimal (base 10) and vice versa;

20
Q

What is interpolation?

A

It is a method of constructing new stimulated data points to fill in the gaps.

21
Q

What does the scan converter allow you to do?

A

22
Q

What is the goal of fill-in interpolation?

A

To fill in the gaps of missing data in a way that cannot be detected by the observer.

It is a form of preprocessing.

It improves visibility to see around the boarders of round structures.

23
Q

Describe Write:

A

Image you get before you freeze.

It is clear.

It zooms to an area of interest and writes to full SC matrix.

24
Q

A

Image you get after you freeze.

It is blurry.

Read from SC matrix only. Area of interest after “freeze”

25
Q

What is pre-processing?

A

It is conditioning prior to storing in SC

26
Q

What is post-processing?

A

Conditioning after storing in SC

27
Q

What are some output devices?

A
• Montior
• Raster,interlaced
• Hardcopy
• Digital storage
28
Q

What are some recording techniques?

A
• Multiimage camera
• Video tape
• SVHS
• VHS
29
Q

How many lines does SVHS have?

A

400

30
Q

How many lines does VHS have?

A

200

31
Q

What does the monitor do?

A

It interlaces which increases frame build up.

32
Q

If you write an image from the transducer to memory what kind of interlacing is yield?

A

Vertical

33
Q

If you read the image from memory to the monitor what type of interlacing will you yield?

A

Raster

34
Q

What does a Roster scan do?

A

It converts vertically collected data.

35
Q

What is the rastor scan problem?

A

Frametime= 1/30 sec.

36
Q

What is the inverse of time?

A

frequency

37
Q

1/ (1/30)=

A

30 Hz

38
Q

When can the eyes detect changes?

A

<60 Hz which is called the strobe effect.

39
Q

Gray scale imaging was initially made possible with the use of what?

A

Scan converters

40
Q

What do scan converters do?

A

FIrst store information and later display it.

41
Q

What is the storage image information in the scan converter called?

A

Writing.

42
Q

What is called when the image data is transfered from the scan converter for display on the monitor?

A

43
Q

What does the scan converter translate the infromation to and from?

A

It translates infromation from the spoke formate into the video format.

44
Q

How were scan converted originally constructed?

A

From analog technology.

45
Q

Modern_________ scan converters use computer technology.

A

Digital.

46
Q

What was the first type of scan converter and made gray scale imaging possible?

A

Analog scan converter

47
Q

What are the advantages of digital scan converters?

A
• Uniformity
• Stability
• Durability
• Speed
• Accuracy
48
Q

What are the two important elements of digital scan converters?

A
1. Pixel
2. Bit
49
Q

What is the smallest building block of a digital picture?

A

Pixel.

50
Q

What is a bit?

A

It is the smallest amount of computer memory.

51
Q

A byte is a group of….

A

eight bits

52
Q

A word of computer memory consists of…..

A

two bytes or bits

53
Q

What is prepocessing?

A

It is the manipulation of image data before storage in the scan converter.

54
Q

What is postprocessing?

A

It is the manipulation of image data after storage.

55
Q

What does the amplifer do?

A

It corrects for amplitude loses with attenuation.

It raises all echo signals proportionally.

56
Q

What is demodulation?

A

It is the process of extracting the low doppler frequency from the transducer’s carrier frequency.

57
Q

What does the demodulator do signals?

A

It seperates phased shifted signals into two parts.

58
Q

What does mixing a demodulator to a baseband do?

A

It changes into a range humans can hear.

20 Hz to 20 Khz

59
Q

What do wall filters do?

A

They eliminate low frequencies associated with slow moving objects.

60
Q

What is the doppler equation ?

A

Fd=(2)(v)(f0)(cosø)/C

Fd=doppler shift

f0= transducer frequency

v=velocity

ø= angle of insonation

c= spped of US in soft tissue

61
Q

How do the speaks present themselves?

A

One speaker displays forward flow.

One speaker displays reverse flow.

62
Q

How do the speakers aid in learning?

A
• Begin eith normal patients
• listen to signal
• Correlate to on screen waveform
• Confirm
• Profress to abnormal patients
63
Q

What is Fast Fourier Transformation bins?

A

It is a mathematical technique for separating spectrum of fd to descrete velocity bins.

64
Q

What is the frequency porporitonal to?

A

velocity

65
Q

What is the amount of frequency porpotional to?

A

Gray scale brightness

66
Q

What is an artifact?

A

It is not a 1-to-1 correspondence between image and object being scanned.

67
Q

What is the assumptions of an artifact?

A

The reflector lies along the thin beam line.

68
Q

What is echo porportional to?

A

echogenicity of objects.

related to impedance.

69
Q

What are the 3 classifications of attenuation?

A
1. Locational
2. Attentuation
3. Doppler
70
Q

What are the type of locational artifacts?

A
1. Speed error
2. Refraction
3. Reverberation
4. Grating lobe/side lobe
5. Mirror image
6. Multiple reflections
7. Slice thickness artifact
71
Q

Describe locational speed error

A

should be 1540 m/s.

if less→shallower than actual

if greater→deeper than actual

72
Q

Describe location refraction?

A

It occurs when a sound wave strikes a boundary that has a different progragation speed.

2° media of different Z→Snell’s law

73
Q

Describe locational reverbation:

A

Appears on the display as multiple,equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam.

74
Q

What are the two types of reverberation?

A
1. Comet Tail→Anatomic structure
2. Ring down→Gas bubbles
75
Q

What is the solution of locational grating lobe?

A

Apodization which reduces power/energy delivered to outer elements.

76
Q

What does a mirror image need?

A

A mirror.

e.g. tibia

77
Q

What is slice thickness artifact?

A

Its when the transducer picks up outer curvature of bladder in elevation plane which looks like sludge/thrombus.

78
Q

What are some formes of attentuation?

A
• below highly attenuating structures
• e.g. bone, dense tissue
• Enhancement (brightening)
• blwo lowly attenuating structures
• e.g. full bladder, fluid filled cysts.
79
Q

What happens if the nyquist samples <2x the during a cycle?

A
• Loss of increased frequencies
• “wrap-around” effect
• “Apparent” reversal of flow.
80
Q

How should you avoid wrap around

A
• Increase velocity scale
• Decrease baseline
• Decrease frequency probe
• Increase 90°
• Use higher PRF mode
81
Q

How do you avoid NL aliasing?

A
• Increase PRF
82
Q

Equation for PRF?

A

PRF=1/PRP

83
Q

How do you get a shallower sample depth?

A
• Decrease PRP
• Increase PRF
• Increase NL
84
Q

What is grating lobe?

A

It happens when there is energy outside of the beam.