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CORE > Physics Ch 8 US > Flashcards

Physics Ch 8 US Flashcards

1
Q

loss of 3 dB (-3 dB) –> signal intensity (power) –> dec/inc/no change? by how much?

A

dec by 50%

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2
Q

what is “half-value” thickness (HVT)?

A

tissue thickness that reduce/attenuate US intensity by 3 dB

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3
Q

US –> higher freq –> scatter –> dec/inc/no change?

A

inc

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4
Q

higher freq –> half value thickness (HVT) –> dec/inc/no change?

A

dec

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5
Q

attenuation –> loss of intensity of US beam (d/t absorption/scattering) –> what is rate of attenuation in soft tissue?

A

0.5 (dB/cm)/MHz

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6
Q

what factors determine strength of echoes? (2)

A
  • angle

- impedance

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7
Q

higher freq US probe –> has thinner or thicker xl?

A

thinner

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8
Q

which component of the US probe contributes to spatial resolution (axial resolution)?

A

dampening block

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9
Q

thin dampening block:

  • light vs heavy damping?
  • low vs high Q?
  • short vs long spatial pulse length?
  • narrow vs broad bandwith?
A
  • light damping
  • high Q
  • long spatial pulse length
  • narrow bandwidth
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10
Q

thick dampening block:

  • light vs heavy damping?
  • low vs high Q?
  • short vs long spatial pulse length?
  • narrow vs broad bandwith?
A
  • heavy damping
  • low Q
  • short spatial pulse length
  • broad bandwidth
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11
Q

light damping (high Q) –> used for what kind of US study? why?

A

Doppler –> preserve velocity data

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12
Q

heavy damping (low Q) –> pro? (1)

A

high spatial resolution (axial resolution)

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13
Q

US probe –> matching layer –> fx?

A

minimize acoustic impedance differences bw transducer & pt

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14
Q

US probe –> matching layer –> optimal thickness (relative to wavelength)?

A

1/4 wavelength

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15
Q

higher freq –> near field (Fresnel zone) –> inc/dec/no change?

A

inc

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16
Q

larger US probe –> near field (Fresnel zone) –> inc/dec/no change?

A

inc

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17
Q

higher freq –> far field (Fraunhofer zone) –> divergence –> inc/dec/no change?

A

dec

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18
Q

US beam –> what is focal zone (focal depth)? what is its significance?

A

spot bw converging & diverging beams:

  • narrowest beam
  • area of max intensity

==> best lat resolution

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19
Q

what are the 3 dimensions in US?

A
  • axial
  • lat
  • elevation (slice thickness)
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20
Q

2 objects need to be what distance apart to be seen as 2 separate objects?

A

1/2 spatial pulse length

21
Q

US –> what is axial resolution?

A

ability to tell apart 2 closely spaced objects in the direction of the beam

22
Q

US –> what is lateral resolution?

A

ability to resolve objects in a direction perpendicular to beam direction

23
Q

axial resolution –> constant at different depths –> T/F?

A

T

24
Q

higher freq –> lat resolution –> dec/inc/no change?

A

inc

25
Q

US probe –> larger diameter –> lat resolution –> dec/inc/no change?

A

inc

26
Q

US probe –> higher scan line density –> lat resolution –> dec/inc/no change?

A

inc

27
Q

side lobe artifact –> occur more w linear vs phased array transducer vs no effect?

A

linear

28
Q

power doppler –> Doppler angle does not matter –> T/F?

A

T

29
Q

Power doppler –> produces aliasing artifact –> T/F?

A

F (color & spectral doppler do produce aliasing artifact. Power does not)

30
Q

doppler –> aliasing –> occur when velocity is higher than what?

A

Nyquist freq

31
Q

doppler –> aliasing artifact –> remedy? (2)

A
  • inc pulse repetition freq (PRF)

- inc scale

32
Q

can adjust what control to brighten or darken image? (2)

A
  • output power (transmit gain)

- receiver gain

33
Q

dark image –> want to brighten it up –> how do the following brighten image?

  • output power (transmit gain)
  • receiver gain
A
  • output power (transmit gain): inc power of US beam

- receiver gain: inc strength of sound that returned to transducer

34
Q

dark image –> want to brighten it up –> adjust output power (transmit gain) vs receiver gain –> which is optimal? why?

A

receiver gain

inc output power (transmit gain) –> degrade lat resolution

35
Q

time gain compensation –> fx?

A

compensate for loss of echo strength caused by depth of reflector –> uniform brightness from top to bottom

36
Q

how does pulse length relate to bandwidth?

A

pulse length = 1/Bw

37
Q

harmonics –> pros? (3)

A
  • improve lat resolution
  • dec side lobe artifact (grating lobe artifact)
  • dec superficial reverberation artifact
38
Q

harmonics –> generated in superficial or deep tissue?

A

deep

39
Q

what is compound imaging? clinical significance?

A

transducer –> US beams in mult directions –> sharpen edges of object

40
Q

compound imaging –> cyst –> post shadowing –> dec/inc/no change?

A

no more post shadowing

41
Q

harmonic vs normal US –> what happens to…

  • comet tail
  • reverberation
  • through transmission
  • acoustic shadowing
  • speckle noise
  • side lobe/grating
A
  • comet tail: inc
  • reverberation: dec
  • through transmission: inc
  • acoustic shadowing: inc
  • speckle noise: dec
  • side lobe/grating: dec
42
Q

what is “intensity”?

A

power/area

43
Q

amplitude –> squared –> what happen to intensity?

A

square amplitude –> 4x intensity

44
Q

cavitation –> more likely to occur with…

  • low vs high freq
  • low vs high pressure
A
  • low freq

- high pressure

45
Q

NCRP –> risk-benefit decision at?

  • thermal index (TI) of??
  • mechanical index (MI) of??
A
  • TI >1.0

- MI >0.5

46
Q

pulse repetition freq (PRF) —> formula?

A

PRF = c/2D

c = 1540 m/s 
D = depth
47
Q

soft tissue –> attenuation coefficient?

A

0.5 dB/cm/MHz

48
Q

How does mechanical index depend on transducer frequency?

A

Inversely proportional to the square root

49
Q

What is the wavelength of a 1.5 MHz wave?

A

~1mm

1.5 MHz / 1540 m/s = 0.00097 m = 0.001 m = 1mm

CORE (33 decks)

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