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Imaging Review CCPM > ULTRASOUND > Flashcards

ULTRASOUND Flashcards

1
Q

US matrix size

A

512x512, 1 byte/pixel, 0.25 MB

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2
Q

hypoechoic and hyperechoic image

A
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3
Q

mirror artifact image

A

causing the appearance of “liver” or “spleen” inside the lung

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4
Q

shadowing artifact image

A

-hard things like bone, stones

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5
Q

enhanceent artifact image

A

-liquid filled things like bladder, cyst

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6
Q

ring down artifact image

A

when fluid is trapped in a tetrahedron of air bubbles, the ultrasound waves reflect infinitely and result in an infinitely long vertical echogenic line.

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7
Q

comet tail artifact

A

Comet tail artifact is a form of reverberation artifact. In comet tail artifact the two reflective surfaces are closely spaced together (such as the bevel of a metallic needle). The reflective surfaces are so close that it is difficult to distinguish between each reflected echo.

Comet tail artifact is different from ring down artifact (described next) because the comet tail artifact dissipates with depth

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8
Q

lateral resolution compared to axial

A

4X worse than axial and becomes worse as distance from transudcer increases

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9
Q

what is lateral resolution determined by

A

US beam width
increasing lines per frame also increases resilution

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10
Q

assumptions in US

A

-echo depth ~ echo time
-sound travels in straight lines
-attenuation is uniform

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11
Q

Doppler effect- what objects have higher f?

A

-objects going toward detector

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12
Q

doppler shift formula

A

delta f = 2 v cos(theta) f/c

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13
Q

PFR for Doppler

A

must be 2X max expected doppler shift
PFR ~ 8 kHz

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14
Q

length of near field

A

D^2/4 lambda
D is transducer diameter

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15
Q

formula for PFR

A

frame rate * lines per image
each pulse is a line of sight

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16
Q

intensities for B mode vs M mode vs Doppler

A

B mode 10 mW/cm2
M mode 4X higher
Doppler 50x higher

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17
Q

duration of pulse

A

1 us

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18
Q

cavitation

A

creation and collapse of microscopic bubbles

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19
Q

thermal index of 1

A

increase in temperature of 1 degree celcius

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20
Q

what uses A ode imaging

A

ophthalmology
-depth on horizontal axis, echo intensity on vert

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21
Q

how many lines of sight in US image

A

100

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22
Q

PRF typical rate

A

4000 pulses/s, listening interval of 250 us

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23
Q

what corrects for attenuation at depth

A

depth gain compensation

24
Q

T-M imaging

A

time on horizontal axis and depth on vertical axis

25
Q

how many frames per second is typical

A

30

26
Q

what does temporal resolution depend on?

A

PRF
line density
FOV

independent of pulse length

27
Q

mechanical index

A

estimates change of inducing cavitation

28
Q

what is line density

A

of lines per image/FOV

29
Q

how to increase line density

A

reduce frame rate
but this reduces temporal resolution
it improves lateral resolution

30
Q

harmonic imaging receives signals at what frequency

A

2X transmit frequency

31
Q

elevational resolution

A

refers to planes perpendicular to the image plane
aka slice thickness
depends on height of transducer elements
can improve using 1.5D arrays

32
Q

what can make something appear as reverse flow?

A

aliasing

33
Q

reflected US intensity

A

((Z2-Z1)/(Z2+Z1))^2
Z is impedance

34
Q

Impedance of air, tissue, bone, PZT

A

0.01 1, 5, 20

35
Q

what organs scatter vs don’t scatter

A

-get scatter when object is smaller than wavelength
-kdiney, pancrease, spleen, and liver scatter
-bladder and cysts show black

36
Q

does axial resolution vary with depth?

A

no, but lateral does

37
Q

US spectral shift

A

plot Doppler frequency shift as a function of time
-gives info on blood flow

38
Q

sound velocity in bone

A

4100 m/s

39
Q

pulse duration and frequency relationship

A

delta f * delta t = 1/(2pi)

40
Q

attenuation through tissue vs through bone

A

f0.5dB/cm/MHz for tissue, musle
f^20.5dB/cm/MHz

41
Q

equation for lateral resolution

A

lambda * F/2a
F is focal length
2a is aperture of transducer

42
Q

impedance of matching layer

A

Zmatching layer = root(Ztransducer*Zskin)

43
Q

frequency where mechanical energy is best converted into electrical enerrgy

A

Q= (sound velocity in crystal)/(2*crystal thickness)

44
Q

time it takes crystal to decay from resonant to unexcited

A

Q/(2pifres)

45
Q

divergence of far zone

A

phi= arcsin(1.2lambda/D)
D=aperture diameter

46
Q

types of averaged US intensity

A

temporal
pulse averaged

47
Q

focused transducer

A

use curved crystal- get constructive interference at a point

48
Q

phased array

A

-crystals can be excited independently
-by exciting crystals with certain time delays, can do depth focusing and steering

49
Q

size of object versus lambda- effect on US image

A

d»> lambda- strong echoes
d&laquo_space;lambda- scattering (speckle)
d~ lambda- graininess (structure)

50
Q

time gain amplification is log or linear?

A

usually log

51
Q

can sound waves travel in vaccuum?

A

no

52
Q

how to get final attenuation in US

A

add up DBs

53
Q

divergence of the far field

A

sin(theta)=1.22lambda/D

54
Q

harmful US power

A

0.1W/cm2

55
Q

narrow bandwidth

A

light damping, high Q

Imaging Review CCPM (11 decks)

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