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Flashcards in RPVI-Physics Deck (107)
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1

Things we need to know about sounds.

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

2

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

water
low pitch (higher travel less distance)

3

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

small (like a bat)

4

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

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

5

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

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

6

which is slowest to fastest

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

7

what is the measure of sound velocity

M/sec or mm/usec

8

What is the equation to determine depth?

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

9

What is the velocity of sound?

1540 m/s
1.54 mm/usec

10

What is frequency?

one cycle of compression and rarefaction of a sound wave.
frequency is measured by hertz

11

what is one Hertz?

one cycle per second

12

what range is audible sound in hertz?

20-20,000

13

what do we use for vascular applications?

3-15 MHz

14

What is the equation for wavelength?


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

15

how many micro sec in a sec?

1 million

16

what gives better resolution higher or lower frequencies?

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

17

what is amplitude measure by?

decibels
it is a pressure

18

what happens to sound intensity as it propagates?

it loses energy

19

what is this loss called?

attenuation

20

What is one decibel?

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.

21

What things is attenuation a sum of?

reflection
refraction
absorption
scatter
divergence of the wave front

22

What is the half power distance of sound?

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

23

Does air have a short or long half power distance?

very short

24

What is the average attenuation for soft tissue?

0.5 dB/cm/MHz

25

what is reflection depended on ?

acoustic impedance
beam angle

26

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

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

27

what are smooth or specular reflectosreflectors?

needs a 90 angle to be seen
imtima, walls of cyst, venous valves

28

why does acoustic interface cause reflection?

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

29

how do you calculate impedance?

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

30

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

away

31

What is snells law?

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

32

what happens to heat and sound travel?

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

33

What is sound scattering?

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

34

What is it caused by?

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

35

what is the number of events per unit time?

frequency in time

36

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

inverse
inverse
direct

37

What is a transducer?

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

38

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

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.

39

What modes are available for linear transducers?

standard
or wide-mode

40

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

rectangular
trapazoid to see wider images (sound is angled at edges0

41

What are curvilinear transducers used for?

abdo aorta
deep vessels

42

what does the image look like for curvilinear?

edges are curved

43

what probe can be used for large patients with folds?

trnasvaginal

44

what are sector transducers used for?

trans-cranial
cardiac
between ribs
they have small footprint

45

what does the image look like for sector transducer

triangular with tip cut off
wide mode linear looks similar but top is much wider

46

what is the piezoelectric element in a transducer?

converts sounds to electricity and electricity to sound

47

what does the matching layer of a transducer do?

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

48

What is the damping layer

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

49

what is the order of these elements of a transducer

protective membrane
matching layer
crystals
damping layer
electronics

50

what is the pulse echo principle?

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

what is b-mode

brightness mode

52

What are prerequisites for B-mode imaging

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

53

What does the brightness of the image mean?

it represents the strength of the echo.

54

what is depth on an US machine?

the maximum time that the unit 'listens'
longer means deeper

55

What does overall gain do?

it amplifies all of the echoes.
its magnifying the electrical impulses before it gets to the monitor

56

What is TGC?

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

57

what does write magnification do

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

58

how is focus best used?

keep the focus at or just below area of focus

59

what is spatial resolution?
what are the different types of spatial resolution?

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

What is temporal resolution?

how events are happening over time
i.e. blood flow events

61

What is image uniformity

machines ability to place echoes at their correct depth.

62

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

16 frames per sec gives smooth image

63

what factors change the frame rate?

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

64

what is the pulse repetition frequency PRF?

number of echoes produces per second
1 pulse per millisec = PRF of 1000

65

what depth of field of views correspond to what PRF?

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

66

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

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

What other function affect frame rate?

pulsed doppler
color doppler
power doppler
dynamic range
smoothing

more lines are needed to get the information
slower PRF

68

What won't affect frame rate

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

69

how should the notch of the transducer be placed?

towards the head for sagittal or longitudinal scans
or towards the right for transverse scanning

70

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

the left (called superior cranial)
right called inferior or caudal

71

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

left
right

72

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

anterior

73

what does echogenic?

subtance has echoes in it

74

hyperechoic

more echoes or brighter then surrounding material

75

hypoechoic

tissue is surrounds by tissue that is brighter then it

76

anechoic

there are no echoes in a substance
black

77

isoechoic

two areas have same level of brightness

78

what are specular reflector

smooth reflector require 90 angle to be seen
like gortex graft, intima

79

nonspecular reflector

rough reflector does not need 90 angle
adventitia

80

What US assumption can lead to error?

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

81

What is an artifact?

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

82

What is a mirror artifact?

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

how do we eliminate the mirror image?

can the angle of the transducer

84

what different ways can artifacts occur?

mirroring
twining
side lobes
reverberation
comet tail artifact

85

How are side lobes produced

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

86

what is reverberation?

echoe propagates back and forth multiple times between an object

87

what is comet-tail artifact?

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

88

what is an acoustic shadow?

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

89

what is acoustic enhancement?

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

90

what mode of imaging compounds and reduces these artifacts?

harmonic
compound (colour also goes on an angle)

91

What is twinkling artifact?

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

92

What is the equation for doppler shift?

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

what happens when theta = 90?

cos 0 = 0
don't ever really get 90 because of the echoes form a cone

94

How do we solve for velocity?

v=1/2F deltac /f cos0

95

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

increases
decrease towards zero
increase

96

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

underestimate velocity

97

what angle should you keep the transducer and why?

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

98

what is continuous wave doppler?
disadvantages?
advantages

2 piezo simultaneous transmitt and received
echo, OB,

no depth position, minimal global info
aliasing cannot occur

99

what is pulsed doppler?
advantages
disadvantage

timed or pulsed so we can

control the depth

minimal global info
can have aliasing


100

what is aliasing?

erroneous representation of flow
occurs when doppler shift > 1/2 PRF

101

how do you optimize pulse doppler?

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

what decreases aliasing?

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

how do we avoid aliasing?

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

what can we measure in pulsed doppler?

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

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

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

106

what is spectral broadening?

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

107

what is the nyquist limit?

doppler shift at which aliasing begins
more then 1/2 PRF