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physics review > Test 2 > Flashcards

Test 2 Flashcards

1
Q

what are annular arrays?

A

concentric rings of piezoelectric material

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2
Q

what does annular arrays do for us?

A

no electric focus, all natural focusing

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3
Q

what produces multiple foci?

A

smallerst layer to larger layer

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4
Q

how we do make mulptiple foci now with our machine?

A

electronic focusing and image pre-processing

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5
Q

what are some invasive transducers?

A
  • transvaginal
  • transrectal
  • transesophageal
  • cathedar mounted
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6
Q

what does invasive trasnducers allow for?

A

closer to the tissues-higher res

less attenuation

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7
Q

attenuation equation

A

A= 1/2f x l

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8
Q

what factors are we affecting with invasive transducers?

A

decreasing length by getting closer to tissues

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9
Q

what is resolution?

A

visably seperating 2 structures

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10
Q

what resoltuion is apart of the transducer?

A

detail

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11
Q

what are aspects of resoltuion?

A

detail
contrast
temporal

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12
Q

what are the 3 aspects of detail resolution?

A
  • lateral
  • axial
  • elevational
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13
Q

axial resoltion?

A

minimum reflector seperating objects ALONG the scan line

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14
Q

Axial res equation

A

Axial res (mm) = SPL/2

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15
Q

how do we improve axial resolution?

A

SPL-smaller the better

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16
Q

how do we reduce wavelength?

A

altering freq

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17
Q

how do we reduce number of cycles?

A

reduced by damping

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18
Q

laterla resolution?

A

seperating objects that are PERPINDICULAR to the scan line

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19
Q

lateral resolution equation?

A

lateral res (mm)= Wb

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20
Q

elevational resolution

A

section thickness/partial volume artifact

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21
Q

what are characteristics of blood flow?

A
  • volumetric flow rate (poiseulle equation)
  • types of flow
  • continuity rule
  • bernoulli effect
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22
Q

what is volumetric flow rate?

A

volume of blood passing a point per second/minute

LONG STRAIGHT TUBE

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23
Q

when does blood only flow?

A

only if there is a pressure gradient

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24
Q

what is volumetric flow rate equation?

A

Q=P/R

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25
Q

what is Poiseuille’s equation?

A

Q porp. Pd4/ln

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26
Q

what are the types of flow?

A 
Laminar
   -plug
   -parabolic
   -disturbed
Non Laminar
   -tubulent
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27
Q

what is the average flow speed in parabolic hemodynamics?

A

1/2 fastest speed

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28
Q

is distubed flow still laminar?

A

yes (non parobolic)

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29
Q

what flow is non laminar?

A

turbulent

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30
Q

how is pulsatile arterial flow characterized?

A
  • compliance of the vessel walls

- expansion and contraction of non-rigid vessel walls

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31
Q

what does compliance allow for?

A
  • added forward flow

- reversal of flow

32
Q

what is the windkissel effect?

A
  1. pulse forces fluid into the vessel and vessel distends
  2. aortic valve closes, decreasing driving pressure
  3. vessel contracts, pushes blood forward
33
Q

reversal of flow?

A
  • due to contraction of extended vessels during diastole

- no valves to prevent backward flow

34
Q

what is the continuity rule?

A

keep vol. flow rate contant speed will increase

35
Q

what is the continuity rule equation?

A

Q=V x A

36
Q

what tube is the continuity rule for?

A

SHORT SEGMENTS

37
Q

for contunituty rule of area decreaes what happens to velocity?

A

increased (keep Q constant)

38
Q

what is the bernoulli effect?

A

decrease in pressure in regions of high flow speed

39
Q

what is velocity inversly proportional to?

A

pressure

40
Q

what is the doppler effect?

A

change in frequency caused by the motion of a source, reflector or reciever

41
Q

when is the doppler shift positive?

A

gettting closer and the freq goes up

42
Q

what is the doppler equation (t and r)

A

Fd = Fr -Ft

43
Q

what is the doppler equation?

A

Fd = 2 x fo x v/c

44
Q

what is the doppler equation with veolocity?

A

v= 77 x fd/ fo

45
Q

what are the steps of doppler?

A
  1. transducer sends a pulse to a moving object
  2. transducer recieves new f and calculates doppler shift
  3. doppler shift depends on the objects velocity
  4. machine calculates speed based on doppler shift
46
Q

how much doplper shift will occur if the angle of interrogation is non zero?

A

lesser doppler shift will occur

47
Q

cos0

A

1

48
Q

cos30

A

0.87

49
Q

cos60

A

0.5

50
Q

cos1

A

0

51
Q

what happens when the doppler shift is smaller than it should be?

A

the calculated velocity appears smaller

52
Q

what must a sonographer do to acheive an angle close to 0?

A

heel toe

phase (steer)

53
Q

what information are we getting for colour doppler?

A
  • presence
  • direction
  • speed
  • character
54
Q

how many echoes are recieved with colour doppler?

A

10

55
Q

beam former sends digitzed voltages to the __________

A

signal processor

56
Q

signal processor deteects doppler shifted echoes useing___________

A

autocorrelation

57
Q

autocorrelation

A

mathematical technique that determines mean and variance of doppler shift signal

58
Q

how many pulses are sent out per scan line in colour doppler?

A

3-32

59
Q

what does more pulses sent out per scan line do?

A

increase accuracy and sensitivity but it reduces frame rate

60
Q

what does the signal processor calculate and display?

A
  • mean
  • varience
  • power
61
Q

what is power?

A

intensity of echo related to amplitude

62
Q

what does power depend on?

A

reflectors-more reflection more echoes
impedence-higher Z, more echo
concentration of RBC’s-more reflectors, more echo

63
Q

what is the only thing power uses?

A

uses only the power/strength of doppler shifts

64
Q

what are pros of power doppler?

A
  • no aliasing
  • angle independant
  • increased sensitivity
65
Q

what are the cons of colour doppler?

A
  • no direction
  • no flow speed info
  • no flow character
  • cannot catch a stenosis
66
Q

hue

A

colour itself

67
Q

saturation

A

richness of color

68
Q

luminence

A

brightness

69
Q

how does box size affect FR?

A

bigger the box, less lines per frame??

70
Q

what happens when we lower PRF?

A
  • allows to pick up slower flow

- increases chance of aliasing

71
Q

where in the instrument does the gain happen?

A

amplifiers in the beam former

72
Q

what is esemble length?

A

number of pulses used for each colour scan line

73
Q

echoes _______ cut off amplitude will show as colour

A

below

74
Q

stronger echoes show as ________-

A

greyscale

75
Q

what happens when priorty is set too low?

A

noise or artifacts within the vessel are displayed with little colour

76
Q

what happens when priority is set too high?

A

fills the vessel with colour esp. when there is a low signal to noise ratio

77
Q

does duplex scanning happen all at once?

A

no, tranducer does one at a time

-simultaneous does not exist

physics review (1 decks)

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