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Neurosonology > Physics > Flashcards

Physics Flashcards

1
Q

relationship between Pulse Duration and accuracy

A

SHORTER pulse duration INCREASES accuracy. This is because pulse duration = #cycles / frequency. A corollary of this is that high frequency gives better accuracy because HIGH FREQUENCY = SHORT PULSE DURATION.

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2
Q

Relationship between DEPTH and Pulse Repetition Frequency?

A

Depth DECREASES PRF.

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3
Q

Relationship between DEPTH and Pulse Repetition Period?

A

Depth INCREASES PRP, but only the receive time portion. PRP (usec) = depth (cm) / 13 (usec/cm)

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4
Q

Relationship between DEPTH and Duty Factor?

A

Depth INCREASES pulse repetition period, therefore DECREASES the Duty factor.

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5
Q

Duty Factor formula?

A

pulse duration / pulse repetition period x 100.

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6
Q

typical duty factor value?

A

0.001 or 0.1%

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7
Q

What pulse wave characteristics are adjustable?

A

Pulse repetition frequency, pulse repetition period, duty factor.

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8
Q

Temporal intensities from smallest to largest?

A

Ita, Ipa, Imax, Itp

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9
Q

Rank of spatial intensities from largest to smallest?

A

SPTP (largest)> Im > SPPA > SPTA > SATA (smallest)

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10
Q

What is attenuation measured in?

A

Decibels. Measure “relative” changes in intensity.

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11
Q

What generally governs attenuation?

A

path length and sound frequency.

High to low: Gas > solid > liquid

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12
Q

“Attenuation” of +3 dB results in doing what to the intensity signal?

A

Doubling the intensity signal.

+10dB = 10x intensity signal.

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13
Q

What is the relationship between frequency and attenuation?

A

Higher frequency attenuates more; higher frequency sound loses more energy.

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14
Q

What is the relationship between distance traveled by sound and attenuation?

A

Longer distance traveled by a sound wave results in greater attenuation.

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15
Q

What is the relationship between speed and medium?

A

DENSITY INCREASES speed; STIFFNESS DECREASES speed.

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16
Q

Specular reflection

A

Regular surface; back to transducer; organized; unidirectional

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17
Q

diffuse reflection

A

Irregular surface; back to transducer; disorganized

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18
Q

scattering

A

Small tissue interface (smaller than wavelength)
multiple directions
disorganized

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19
Q

Rayleigh scattering

A

Multiple directions
organized
Happens when acoustic wave is redirected in many different directions as a result of striking a small particle. Blood is a Rayleigh scatterer.

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20
Q

Relationship between scattering and frequency?

A

Directly related.

Increased frequency = increased scatter. Includes Rayleigh scatter.

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21
Q

Relationship between Rayleigh scattering and frequency?

A

RS is directly related to f^4.

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22
Q

IRC formula?

A

IRC = Intensity Reflection Coefficient.
IRC (%) = 100 x ((Δ impedance) / (Σ impedance)) ^2.
% of the initial intensity that is REFLECTED.

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23
Q

ITC (Intensity transmission coefficient) formula?

A

ITC + IRC = 1.Therefore, ITC = 1 - IRC.

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24
Q

Requirements for IRC formula?

A

NORMAL INCIDENCE

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25
Q

Snell’s Law

A

V1 x sin (transmission angle ) = V2 x sin (incident angle)

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26
Q

Other names for axial resolution

A

Longitudinal, radial, depth resolution

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27
Q

Attenuation coefficient formula?

A

1/2 x f (in MHz)

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28
Q

Half value layer thickness

A

Like half life. Distance for which sound has to travel to lose HALF of original INTENSITY.

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29
Q

units of Impedance

A

RAYLS. Kg / (m2 x s) . Impedance of Air = 0.0004 Rayls.

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30
Q

Thirteen microsecond rule

A

1 cm depth corresponds to 13 microsec of transit time (time of flight)

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31
Q

Axial resolution formula

A

Ax Resolution = Spatial Pulse Length / 2
= (#cycles x wavelength) / 2
= 0.77 x #cycles / f

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32
Q

relationship between speed of PZT and frequency?

A

Slower PZT speed = LOWER frequency

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33
Q

relationship between thickness of PZT and frequency?

A

Thick PZT = LOWER frequency

34
Q

Mathematical relationship between PZT, frequency, and speed in PZT?

A

Frequency (MHz) = 1/2 x (speed in PZT / thickness (mm))

35
Q

Doppler equation?

A

Frequency shift = 2 x ft x vblood cos Θ / csound

36
Q

What does “scale” on the ultrasound screen correspond to?

A

Pulse repetition frequency. Also can be thought of as “sampling rate”,

37
Q

Focal depth formula?

A

(diam^2)X (f ) / (61.7)

= 1/4 x (diam^2 / wavelength)

38
Q

what does aliasing look like?

A

wraparound of the velocity signal onto the other side of the baseline

39
Q

relationship between gate depth and aliasing

A

Deeper depth = lower PRF = lower Nyquist limit = INCREASED aliasing

40
Q

relationship between transducer frequency and aliasing

A

higher frequency transducer INCREASES aliasing; higher frequencies cause higher Doppler shifts that are more likely to exceed the Nyquist limit.

41
Q

relationship between blood velocity and aliasing

A

Higher blood velocity INCREASES aliasing.

42
Q

Does focusing contribute to attenuation?

A

No.

43
Q

absorption is defined as?

A

transfer of acoustic energy into heat (in tissues)

44
Q

What is the Nyquist limit?

A

the highest Doppler frequency that can be measured w/o aliasing. Nyquist limit = PRF/2.

45
Q

Is axial resolution dependent on the depth of probe?

A

No. Axial resolution is dependent on the SPL, which is then dependent on the wavelength and cycles in the pulse.

46
Q

Characteristics of imaging transducers?

A

Short duration pulses; backing material; reduced sensitivity; lower Q factor; better axial resolution;

47
Q

Quality factor equation?

A

QF = main frequency / bandwidth

48
Q

relationship between duration and bandwidth?

A

High duration = narrow bandwidth, low duration = wide bandwidth

49
Q

relationship between Q factor and pulse length?

A

Short pulse = LOWER QF. Long pulse = HIGH QF.

50
Q

Temporal resolution is proportional to?

A

FRAME RATE (Hz)

51
Q

How does depth influence frame rate?

A

Low depth = INCREASES frame rate. High depth = DECREASES frame rate

52
Q

How does sector size influence frame rate?

A

Increased sector size = increased Tframe = DECREASED frame rate. Therefore, DECREASED temporal resolution

53
Q

How does # pulses per line (foci) influence frame rate?

A

Increased #pulse per line = increased T frame = DECREASED frame rate = dec. temp resolution.
Incidentally this INCREASES lateral resolution.

54
Q

Relationship between transducer DIAMETER and Far field DIVERGENCE?

A

Large DIAMETER = LOW Divergence.

Small DIAMETER = HIGH Divergence

55
Q

Relationship between transducer FREQUENCY and Far field DIVERGENCE?

A

High frequency = LOW Divergence.

56
Q

Relationship between LATERAL RESOLUTION and Far field DIVERGENCE?

A

Less Divergence = Better Lateral Resolution.

57
Q

Best way to get good LATERAL RESOLUTION in the FAR FIELD?

A

Basically, whichever way translates to a LOW divergence. I.e. high diameter transducer and high frequency transducer

58
Q

other words for lateral resolution

A

LATA = lateral, anguilar, transverse, azimuthal

59
Q

where is the lateral resolution the best?

A

at the focus. in general, lateral resolution thought to be “good” in end of near zone.

60
Q

main determinant of lateral resolution is ?

A

beam diameter. Narrow beam = better resolution.

61
Q

Effect of focus on beam diameter?

A

beam diameter DECREASES (smaller) in the near field + focal zone

62
Q

Effect of focus on focal depth?

A

focal depth is DECREASES.

63
Q

Effect of focus on divergence?

A

Divergence INCREASES.

64
Q

Effect of focus on focal zone?

A

Focal zone DECREASES.

65
Q

Effect of #pulse per line (pulse density) on spatial resolution?

A

Improves spatial resolution

66
Q

Amplitude units?

A

Pascals, g/ cubic cm, particle motion in cm

67
Q

Intensity formula?

A

Power/area

68
Q

Relationship between power and amplitude?

A

Power proportional to amplitude ^ 2

69
Q

1 MHz corresponds to roughly what wavelength?

A

1.5 mm

70
Q

Impedance formula?

A

density of medium x speed of sound in medium.

71
Q

What determines speed of sound in a medium?

A

Density (decreases speed)
Stiffness (increases speed)
(High to low): solid > liquid > gas.

72
Q

Tradeoff between frequency, attenuation, and accuracy?

A

Higher frequency = shorter pulse duration and narrowest beam. Therefore, they have the highest accuracy. But higher frequency also = higher attenuation. .

73
Q

Lateral resolution formula?

A

Lateral resolution = (minimum) beam diameter.

74
Q

higher frequency transducers produce _______ beams and _____________ lateral resolution?

A

Higher frequency = NARROW pulse = IMPROVED Lateral resolution.

75
Q

Spatial pulse length formula?

A

SPL = #cycles x wavelength –> inversely proportional to frequency.

76
Q

Relationship between frequency and axial resolution?

A

Higher frequency = shorter spatial pulse length (SPL) = better axial resolution.

77
Q

what is the diameter of the beam at the focus?

A

Half the diameter at the outset of the transducer.

78
Q

How does line density influence temporal resolution?

A

Increased line density means higher Tframe, which translates to DECREASED temporal resolution. This also translates to better spatial resolution.

79
Q

What is the effect of PRP or PRF on temporal resolution?

A

High PRP = LOWER temporal resolution. Low PRF = LOWER temporal resolution.

80
Q

what is the unit of compensation?

A

dB.

81
Q

what does the alteration of “grayscale mapping” correspond to?

A

Receiver compression.

82
Q

ALARA principle

A

As Low As Reasonably Achievable. When modifications of output power or receiver gain are necessary for improving Dx quality, the first + best choice will minimize U/S exposure.

Neurosonology (3 decks)

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