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Vascular Lab > RPVI-Physics > Flashcards

RPVI-Physics Flashcards

1
Q

Things we need to know about sounds.

A

sound doesn’t travel instantaneously (predictable velocities)
sound travels in a straight line
sounds create pressure energy
sounds create echoes

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2
Q

Does sound travel faster in water or air? low vs high pitch.

A 
water
low pitch (higher travel less distance)
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3
Q

Is high frequency sounds better at locating smaller or larger objects?

A

small (like a bat)

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4
Q

What is stiffness and what does is mean for sound velocity?

A

Stiffness refers to the stiffness of bonds between particles and sounds travels faster the stiffer bonds are

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5
Q

What does density refer to and what does that mean for sound velocity?

A

how close particles are together and low density media has fast ultrasound velocities

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6
Q

which is slowest to fastest

A

gases, liquids/soft tissue, solids

air, fat, water, soft tissue, liver, kidney, blood, muscle, bone
fat is not stiff but so low density it travels faster

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7
Q

what is the measure of sound velocity

A

M/sec or mm/usec

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8
Q

What is the equation to determine depth?

A

depth=1/2 velocity mm/us X round trip time ms

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9
Q

What is the velocity of sound?

A

1540 m/s

1.54 mm/usec

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10
Q

What is frequency?

A

one cycle of compression and rarefaction of a sound wave.

frequency is measured by hertz

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11
Q

what is one Hertz?

A

one cycle per second

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12
Q

what range is audible sound in hertz?

A

20-20,000

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13
Q

what do we use for vascular applications?

A

3-15 MHz

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14
Q

What is the equation for wavelength?

A 
V = lamda x Hz
F= C/lambda
distance of one cycle
wavelength is lamda
wavelength is distance
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15
Q

how many micro sec in a sec?

A

1 million

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16
Q

what gives better resolution higher or lower frequencies?

A

high frequencies but the don’t travel as far into the tissue

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17
Q

what is amplitude measure by?

A

decibels

it is a pressure

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18
Q

what happens to sound intensity as it propagates?

A

it loses energy

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19
Q

what is this loss called?

A

attenuation

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20
Q

What is one decibel?

A

10log10 I1/I2
i1/i2 is the intensity ratio the bigger the ratio the greater the decibel
if there is 100000 (5 zeros) then the log of this is 5.

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21
Q

What things is attenuation a sum of?

A 
reflection
refraction
absorption
scatter
divergence of the wave front
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22
Q

What is the half power distance of sound?

A

the distance sound can travel before only half of the sound remains

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23
Q

Does air have a short or long half power distance?

A

very short

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24
Q

What is the average attenuation for soft tissue?

A

0.5 dB/cm/MHz

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25
Q

what is reflection depended on ?

A

acoustic impedance

beam angle

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26
Q

where is reflection occur?
are all the sounds waves reflected?
why is reflection important?

A

at soft tissue interfaces (acoustic interface)
no some continues on
if forms US images

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27
Q

what are smooth or specular reflectosreflectors?

A

needs a 90 angle to be seen

imtima, walls of cyst, venous valves

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28
Q

why does acoustic interface cause reflection?

A

because has different transmission of velocity and different density.
Z= density X velocity = acoustic impedence value (rayles)

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29
Q

how do you calculate impedance?

A

R=(z2-z1)/(z2+z1) x 100 = % sound reflected
(ie X% of sound is being reflected)
if we send the US there and back the % happens twice as it travels back

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30
Q

If the speed of sound becomes faster at the interface does is move towards or away from the perpendicular line of the interface?

A

away

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31
Q

What is snells law?

A

V1 x sin(O1) = V2 x sin (O2)
O = theta
theta is the angle from the perpendicular line of the interface

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32
Q

what happens to heat and sound travel?

A

sounds is converted to heat
more energy is lost at higher frequencies
conversion to heat is less with stiffer media

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33
Q

What is sound scattering?

A

redirection of sound in several directions so only a small fraction of sound energy returns

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34
Q

What is it caused by?

A

interaction with a small reflector (rbc) (rayleigh scatter) or a rough interface
rayleigh scatter makes US possible

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35
Q

what is the number of events per unit time?

A

frequency in time

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36
Q

What is relationship between wavelength and frequency?
frequency and penetration?
frequency and heat production

A

inverse
inverse
direct

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37
Q

What is a transducer?

A

a machine that converts one kind of energy into another energy.

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38
Q

what is the most common vascular transducer? what about for abdo?
what are other special transducers?

A

linear transducer
curved-linear for abdo (convex)
trans-cranial sector transducer
small curved-linear–transvag can be used for deep vessel in grion, under a rib.

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39
Q

What modes are available for linear transducers?

A

standard

or wide-mode

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40
Q

what does the image look like for normal mode on a linear transducer? for wide?

A

rectangular

trapazoid to see wider images (sound is angled at edges0

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41
Q

What are curvilinear transducers used for?

A

abdo aorta

deep vessels

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42
Q

what does the image look like for curvilinear?

A

edges are curved

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43
Q

what probe can be used for large patients with folds?

A

trnasvaginal

44
Q

what are sector transducers used for?

A

trans-cranial
cardiac
between ribs
they have small footprint

45
Q

what does the image look like for sector transducer

A

triangular with tip cut off

wide mode linear looks similar but top is much wider

46
Q

what is the piezoelectric element in a transducer?

A

converts sounds to electricity and electricity to sound

47
Q

what does the matching layer of a transducer do?

A

create acoustic interface that won’t reflect all of our sounds back into the transducer

48
Q

What is the damping layer

A

its under the matching layer

material that prevents the piezoelectric element from ringing more then 1-2 wavelengths before it stops sound production

49
Q

what is the order of these elements of a transducer

A 
protective membrane
matching layer
crystals
damping layer
electronics
50
Q

what is the pulse echo principle?

A

Us sent into patient with a brief pulse
travel through patient and is reflected, refracted, absorbed and scattered
some sound returns to transducers and creates an image

51
Q

what is b-mode

A

brightness mode

52
Q

What are prerequisites for B-mode imaging

A

depth
direction of pulse
amplitude
multiple lines of info obtained and integrated quickly to form image

53
Q

What does the brightness of the image mean?

A

it represents the strength of the echo.

54
Q

what is depth on an US machine?

A

the maximum time that the unit ‘listens’

longer means deeper

55
Q

What does overall gain do?

A

it amplifies all of the echoes.

its magnifying the electrical impulses before it gets to the monitor

56
Q

What is TGC?

A

time-gain compensation

is amplification of distant echoes to correct for attenuation. so farther images are amplified but not closer ones.

57
Q

what does write magnification do

A

select small portion of the screen and scan only that portion of the screen. get more precise image and larger image

58
Q

how is focus best used?

A

keep the focus at or just below area of focus

59
Q

what is spatial resolution?

what are the different types of spatial resolution?

A

ability to discerned on tiny structure from another at closer and closer distances apart.
axial along US beam
lateral across transducer
elevational thickness of US slice (can contrib to error)

60
Q

What is temporal resolution?

A

how events are happening over time

i.e. blood flow events

61
Q

What is image uniformity

A

machines ability to place echoes at their correct depth.

62
Q

how many frames per sec do you need for adequate temporal resolution?

A

16 frames per sec gives smooth image

63
Q

what factors change the frame rate?

A 
lines per frame
depth
# of focal zones
field of view
# of functions running
will all slow down the frame rate
64
Q

what is the pulse repetition frequency PRF?

A

number of echoes produces per second

1 pulse per millisec = PRF of 1000

65
Q

what depth of field of views correspond to what PRF?

A

75 cm = 1000
25 cm = 3000
12.5 cm = 6000
7.5 cm = 10 000

66
Q

what is the usual line density?
why is this important?
how can we overcome that disadvantages?

A

2-6 pulses per line
every pulse produces a line that must travel from the surface of the imaged area to the deepest point and return. the more lines the longer it takes to display image. you trade of TEMPORAL resolution for spatial resolution

lower # of lines, decrease focal zones, write zoom

67
Q

What other function affect frame rate?

A 
pulsed doppler
color doppler
power doppler
dynamic range
smoothing

more lines are needed to get the information
slower PRF

68
Q

What won’t affect frame rate

A 
post-processing
biopsy guides
calipers
scrolling
read zoom
doppler invert
near-field gain
69
Q

how should the notch of the transducer be placed?

A

towards the head for sagittal or longitudinal scans

or towards the right for transverse scanning

70
Q

Which side does the notch appear on the image in sagittal?

A 
the left (called superior cranial)
right called inferior or caudal
71
Q

In tranverse image where does the notch display and what side of the patient does that represent?

A

left

right

72
Q

what do we call the side we are touching the patients skin?

A

anterior

73
Q

what does echogenic?

A

subtance has echoes in it

74
Q

hyperechoic

A

more echoes or brighter then surrounding material

75
Q

hypoechoic

A

tissue is surrounds by tissue that is brighter then it

76
Q

anechoic

A

there are no echoes in a substance

black

77
Q

isoechoic

A

two areas have same level of brightness

78
Q

what are specular reflector

A

smooth reflector require 90 angle to be seen

like gortex graft, intima

79
Q

nonspecular reflector

A

rough reflector does not need 90 angle

adventitia

80
Q

What US assumption can lead to error?

A 
straight line
beam is infinitely thin
constant velocity
each echo comes from shortest pathway
loss of energy is linear and predicatable
81
Q

What is an artifact?

A

image that doesn’t represent in position or intensity any real structure

82
Q

What is a mirror artifact?

A

it creates a pseudo mass.
echo hits vein then behind it the artery the artery reflects an echo and it hits the vein again which sends it back to the artery and then to transducer. a mirror image then appears to be deeper then the artery?

83
Q

how do we eliminate the mirror image?

A

can the angle of the transducer

84
Q

what different ways can artifacts occur?

A 
mirroring
twining
side lobes
reverberation
comet tail artifact
85
Q

How are side lobes produced

A

produced by all multi crystal transducers
interference from multiple piezo
low intensity

86
Q

what is reverberation?

A

echoe propagates back and forth multiple times between an object

87
Q

what is comet-tail artifact?

A

similar to reverberation
series of closely spaced small lines
decrease by using compound imaging
seen best in hypo echoic areas also calcifications

88
Q

what is an acoustic shadow?

A

structure adsorbs, refracts or reflects sound at higher level (>0.5) then there will be an area of decreased brightness behind it

89
Q

what is acoustic enhancement?

A

structure adsorbs, refracts or reflects sound at lower level then there will be an area of increased brightness behind it

90
Q

what mode of imaging compounds and reduces these artifacts?

A

harmonic

compound (colour also goes on an angle)

91
Q

What is twinkling artifact?

A

calcium can also cause colour
happened because of vibrations
get the patient to fremitus and then you can see that it is artifact

92
Q

What is the equation for doppler shift?

A

delta F= (2 f/c) v cos 0

delta F= change in freq (doppler shift)
f = frequency of transducer (average if multiple)
v= velocity of blood flow
0=theta angle of isolation
direction of blood flow and direction of sound waves

93
Q

what happens when theta = 90?

A

cos 0 = 0

don’t ever really get 90 because of the echoes form a cone

94
Q

How do we solve for velocity?

A

v=1/2F deltac /f cos0

95
Q

what happens to doppler shift when blood velocity increases? when doppler angle approaches 90? increase initial frequency?

A

increases
decrease towards zero
increase

96
Q

If you don’t adjust angle in pulsed doppler what happens?

A

underestimate velocity

97
Q

what angle should you keep the transducer and why?

A

60 degrees
can cause error
error increases with increasing angle
still get error 18% at 60 degrees

98
Q

what is continuous wave doppler?
disadvantages?
advantages

A

2 piezo simultaneous transmitt and received
echo, OB,

no depth position, minimal global info
aliasing cannot occur

99
Q

what is pulsed doppler?
advantages
disadvantage

A

timed or pulsed so we can

control the depth

minimal global info
can have aliasing

100
Q

what is aliasing?

A

erroneous representation of flow

occurs when doppler shift > 1/2 PRF

101
Q

how do you optimize pulse doppler?

A

optimize gray scale
select area of interest with appropriate window with reasonable depth
set scale, baseline and doppler gain
set filter to eliminate noise

102
Q

what decreases aliasing?

A 
shallower vessel (because info coming back faster)
size of field of view (longer time to collect data if large FOV)
decrease image processing (colour on)
103
Q

how do we avoid aliasing?

A

adjust baseline (lower it and get wider range of frequency)
increase PRF
increase doppler angle (as approaches 90 doppler shift approaches zero so decrease accuracy but decreases aliasing)
decrease frequency (higher freq equals higher doppler shift)
decrease depth
turn off colour or power doppler
use CW

104
Q

what can we measure in pulsed doppler?

A

ANGLE DEPENDENT
PSV
EDV
acceleration gradient

if you are measuring in cm/s then you need an angle

ANGLE INDEPENDENT
PI (S-D)/M
resistive index RI (S-D)/S
acceleration time
ratios

systolic, diastolic, mean

105
Q

what is spectral analysis?
what is the envelope
what is the spectral window

A

thickness/thin of line on pulsed doppler
the most outside edge
area of black under the envelope

106
Q

what is spectral broadening?

A

when the spectral window is thick
disease
large sample volume (gate is more then 1/3 of the artery)

107
Q

what is the nyquist limit?

A

doppler shift at which aliasing begins

more then 1/2 PRF

Vascular Lab (5 decks)

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