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Physics 2 > Test 1 > Flashcards

Test 1 Flashcards

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1
Q

Diagnostic ultrasound systems are:

A
  • pulse echo systems

- it determines echo strength and location of echo-generating site

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2
Q

echo strength=

A

brightness

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3
Q

what is the location determined by?

A
  • arrival time

- direction of returning echoes

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4
Q

what are the 4 main sections of an ultrasound instrument?

A
  • beam former
  • signal processor
  • image processor
  • display
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5
Q

what does the beam former work with?

A

the transducer

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6
Q

are we dealing with sound or voltage with the beam former?

A

voltage

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7
Q

transmission channels

A

each path to each individual element is a channel

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8
Q

reception channels

A

each path from each individual element is a reception channel

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9
Q

what are the components of the transmitter?

A
  • master synchronizer
  • pulser
  • pulse delays
  • transmit/receive switch
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10
Q

what are the components of the receiver?

A
  • amplifier
  • analog-to-digital converters
  • echo delays
  • summer
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11
Q

what is the master synchronizer?

A
  • coordinates the entire system

- tells the pulser when to fire

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12
Q

why does the master synchronizer wait for the echo to come back before firing the next pulse?

A

prevents range ambiguity

AKA echo-misplacement

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13
Q

what is range ambiguity?

A

incorrect placement of echo along scan line

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14
Q

what is the pulser?

A

produces electric voltages that drive the transducer

-in response transducer produces ultrasound pulse

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15
Q

Fvoltage=

A

Fpulse, Fo

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16
Q

what does Fo range from for most applications?

A

2-20 MHz

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17
Q

PRFvoltage=

A

PRFpulse

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18
Q

why does the PRF voltage equal the PRF pulse?

A

for each voltage pulse one ultrasound pulse is generated

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19
Q

what are the units for f?

A

MHz

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20
Q

what are the units for PRF?

A

KHz

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21
Q

what are the typical values for PRFvoltage? (2D)

A

4-15 KHz

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22
Q

what are the typical values for PRF pulse? (doppler)

A

5-30 KHz

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23
Q

when is PRF operator controlled?

A

doppler

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24
Q

Why is PRF not operator controlled in grayscale?

A

it is automatic

-depth of image will determine PRF (indirect control)

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25
Q

what happens for deeper images?

A
  • echoes take longer to return
  • PRF goes down
  • Frame rate goes down
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26
Q

instrument automatically achieves the highest ____

A

PRF

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27
Q

what happens if we go over 77 cm/ms?

A

an artifact will occur

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28
Q

what happens to the PRF in 2D if depth is increased by 4x?

A

decrease by 4x

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29
Q

what does 2D/grayscale automatically do?

A

accommodates depth

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30
Q

the power or strength of the beam entering the tissue is __________

A

closely related to intensity

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31
Q

stronger voltage =

A

stronger pulse

32
Q

can the pulser be controlled?

A

yes

33
Q

how do we control pulser?

A

“output” dial on some machines

-displayed in dB/%

34
Q

what are pulse delays?

A
  • decide how many elements/crystals are involved

- decide which ones to fire and when

35
Q

what are pulse delays involved in?

A
  • sequencing arrays
  • phasing and steering
  • electronic focusing
  • dynamic aperture control
  • apodization
  • coded excitation
36
Q

what are sequencing arrays?

A

multiple blocks of sound, each producing a scan line

37
Q

what is phasing and steering?

A

microsecond delays between element firings

38
Q

what is electronic focusing?

A
  • Curved delay pattern send sound beam to a focal point

- Adjusting the delay places focus closer or farther away

39
Q

what is dynamic aperture control?

A

pulser+pulse delays

decides the width of our aperture

40
Q

what is apodization?

A

pulser+pulse delays

  • Decreasing the strength to outer elements
  • Reduction of grating lobes in arrays
41
Q

what is coded excitation?

A

normally send one pulse per scan line (ensemble length=1) or can send multiple pulses per scan line (esemble length=3-30)

42
Q

what is another way coded excitation can be used?

A

send 1 pulse, wait, then 2 cycle pulse, wait, e.t.c

43
Q

what does coded excitation involve?

A

decoder in beam former

44
Q

what helps in avoiding range ambiguity?

A

decoder in coded excitation

45
Q

what does coded excitation allow for?

A
  • multiple foci
  • spatial compounding
  • increased penetration
  • increasing contrast resolution
  • B-flow imaging
46
Q

what is B flow imaging?

A

multiple pulses are sent down the same scan line and decoder stacks the received echoes (constructive interference)

47
Q

what does constructive interference do?

A
  • overall higher intensity echo

- makes weak echoes seem brighter

48
Q

what does increased sensitivity do?

A

able to pick up weaker echoes

49
Q

how is B flow different than B mode?

A

picking up very weak echoes (the blood cells themselves)

50
Q

what is the purpose of the pulser?

A

provides the voltage

51
Q

what is the purpose of pulse delays?

A

decides how many elements are involved and which ones to fire and when (linear sequencing, phasing, e.t.c)

52
Q

what type of signals are amplifiers used to receiving?

A

weaker signals

53
Q

what will happen if the amplifier receives a high signal?

A

receiving the stronger voltage from the pulser/pulse delays results in the overload of the amplifier

54
Q

what is the purpose of the T/R regards to amplifiers?

A

it protects the amplifiers from the outgoing voltage

55
Q

what does an amplifier do?

A

returning echo is a mechanical wave and the transducer converts it into an electrical signal and voltage travels to the amplifier

56
Q

what does the power ratio equal?

A

gain (dB)

57
Q

what is amplification opposite of?

A

attenuation

58
Q

what do amplifiers allow for?

A
  • amplification (gain)

- compensation (TCG)

59
Q

what is the attenuation in soft tissue?

A

0.5 dB/cm MHz (one way)

60
Q

lateral gain compensation

A

for adjacent structures that have different attenuation

61
Q

what is a drawback to amplification?

A

weaker echoes from the electric current result in a grainier signal

62
Q

analog-to-digital converters

A

voltage to numbers

63
Q

echo delays

A

same as pulse delays

THESE ARE DIGITAL DELAT LINES NOW

64
Q

summer (adder)

A

signals added together as a scan line

65
Q

reception apodization

A

reducing the returning voltages on the peripheral of the transducer

66
Q

what are the functions of the beam former?

A
  • generating pulses that drive the transducer
  • determining PRF
  • coding
  • frequency and intensity
  • scanning, focusing and apodizing the transmitting beam
  • amplifying the returning echo voltages
  • compensating for attenuation
  • digitizing the echo voltage stream
  • directing, focusing, and apodizong the reception beam
67
Q

Which part of the beam former function does the Pulser perform?

A
  • generates voltage pulses
  • sets the PRF
  • controls power
68
Q

How many cycles are produced by the electric voltages?

A

2/3 cycles per pulse

69
Q

What determines the frequency of the resulting ultrasound pulse?

A

The frequency of the voltage pulse/transducer element thickness

70
Q

why is a transmission channel required?

A

for a more precise control over the beam characteristics

71
Q

What does the Transmit/ Receive switch do?

A

Directs voltage pulses and the delays to the transducer during transmission and then directs echo voltages from the transducer to the amplifier during reception

72
Q

The ultrasound PRF is equal to the __________PRF of the pulser.

A

voltage

73
Q

TGC

A

Corrects for tissue attenuation

74
Q

gain

A

Increases all amplitudes

75
Q

analog

A

porportional

76
Q

digital

A

discrete (numbers)

77
Q

what does TGC compensate for?

A

attenuation

Physics 2 (4 decks)

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