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US Flashcards

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1
Q

What is the range of human hearing? What is considered US?

A

20-20,000 HZ

> 20,000 HZ = US

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2
Q

Define below and provide units where relevant

A
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3
Q

What is the approximate geometry of an ultrasound beam?

A
  • LONGITUDINAL WAVE: Two distinct regions:

Convergent beam -> near field

Divergent beam -> far field

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4
Q

Define reflection. What features dictate reflectivitity? What is the reflection coefficient calculation?

A
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5
Q

Define intensity. What are dB?

A

Rate at which energy passes through a unit area (= power in wave divided by area over which power spread)

Different units used e.g. include (mW/cm2) and watts per centimeter squared (W/cm2)

dB = RELATIVE INTENSITY. Comparison of intensities converted logarithmically. USED FOR ATTENUATION COEFFICIENT

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6
Q

Equation for reflection coefficient AND intensity transmission coefficient

A

TRANSMISSION COEFFICIENT = 1 - RI!! Just a measure of how much energy transmitted, with 1 = to complete transmission

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7
Q

Define acoustic impedance inc. unit and equation

A
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8
Q

Define refraction. What equation is used to describe effect?

A
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9
Q

Define 3 types of reflector

A

TISSUE INTERACTIONS

  • Acoustic scattering: due to small particle reflectors - characteristic of tissue or organ

BOUNDARY

  • Non-specular: Approximately same as wavlength or smaller -> ROUGH reflector
  • Specular: Large reflector relative to wavlenth -> SMOOTH reflector
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10
Q

List 4 factors that influence AMPLITUDE of signal from insonated tissue

A
  • Number of scatters per unit volume (Less amplitude if more scatters)-
  • Size of scatterers
  • Acoustic impedance differences at scatterer surfaces (Increase amplitude if more impedance)
  • Freq (inc scatter from non-specular reflectors with high freq)
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11
Q

What interactions are most responsible for attenuation?

A

SCATTER and ABSORPTION

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12
Q

Define attenuation and attenuation coefficient, including units. WHAT IS THE RULE OF THUMB!!

A
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13
Q

What is HVT in US?

A
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14
Q

Define Spatial Pulse Length (SPL)

A
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15
Q

Name 2 methods to improve axial resolution

A

REDUCE SPL

  • Increase frequency (and thus smaller wavelength)
  • Shorten pulse duration / number of cycles
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16
Q

Calculate SPL and resolution for 5MHz signal (wavelength 0.31mm) and 3 cycle pulse

A

0.93mm PULSE = SPL

Axial resolution = 1/2 SPL = 0.47mm

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17
Q

What factors are most important for AXIAL and TRANSVERSE (Azithmul) resolution?

A

Axial = SPL

Trans = Beam width

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18
Q

Define PRF, PRP and pulse duration

A
  • Pulse repetition frequency (PRF)
    • Number of pulses/s (kHz)
  • Pulse repetition period (PRP)
    • Time from beginning of one pulse to beginning of next (ms)
  • PRF RECIPROCAL OF PRP
    • As repetition frequency goes up, repetition period goes down
  • Pulse duration (microseconds)
    • ​Period (of single cycle) x number of cycles per pulse
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19
Q

Detail PRF

A
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20
Q

Detail PRP

A
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21
Q

Detail pulse duration

A

NB: INCORRECT EQUATION -> Wave period X number waves in a pulse

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22
Q

Detail duty factor

A
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23
Q

How does frequency in PW doppler compare to CW?

A
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24
Q

Define bandwidth, fractional bandwidth, and quality factor (Q)

A
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25
Q

How does dampening relate to bandwidth and Q factor?

A
  • Increase dampening:

DECREASE SPL

INCREASE BANDWIDTH

DECREASED Q FACTOR

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26
Q

Define range and how distances are calculated by US

A
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27
Q

What factors increase acoustic impedance?

A
  • Increased density
  • Increased propagation speeds

THINK ABOUT THE EQUATION!

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28
Q

What is the speed of sound in ST?

A

1540m/s (1.54 mm/microsecond)

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29
Q

For a reflector at 5cm depth, calculate pulse round trip time

A

d = 1/2 (c x t)

100mm = 1/2(1.54mm/mcsec x t)

100 / 1.54 = 65 microseconds (ROUND TRIP TIME)

TIme to reflector = round trip time / 2 = 32.5microsec

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30
Q

What is the rule that can help with pulse round trip time?

A
  • Pulse round trip time = 13 microseconds / cm from source to reflector!!

**ANSWER NEEDS TO BE DIVIDED BY 2 TO CALCULATE REFLECTOR DISTANCE**

1 sec = 1microsec x10-6

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31
Q

TABLE

A
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32
Q

Define wavelength, propagation speed and frequency. How do they relate?

A
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33
Q

A 5 MHz beam travels from soft tissue into fat. Calculate wavelength in each medium and determine % wavelength change

A

Frequency = 5MHz (cycles/s)

Speed = 1540m/s AND 1450m/s

1540 / 5, 000, 000= 0.000308m = 0.31mm

1450 / 5, 000, 000 = 0.000290m = 0.29mm

Wavelength expressed in mm!!

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34
Q

What is the speed of sound in ST and FAT?

A

ST = 1540m/s

Fat = 1450m/s

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35
Q

How do spatial resolution and attenuation relate to wavlength and frequency?

A

Resolution -> increases with smaller wavelength (higher frequency)

Attenuation -> Increases with smaller wavelength (higher frequency)

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36
Q

TABLE

A
37
Q

What features determine size of near field?

A
  • Unfocused single array:

Tranducer diameter

Frequency

- Multiple element array

Effectrive diameter (excitation of groups of elements)

INCREASES with increasing width or frequency (“Aperture”)

38
Q

What factors affect beam divergence in the far zone?

A

APERTURE!

  • Frequency: Higher frequency, less divergence
  • Beam width: Larger width, less divergence
39
Q

List 3 things that can create beam focusing, and 3 things that limit beam focusing

A

Cause:

  • Curved elements
  • Lens
  • Phasing

Limiters:

  • Wavelength
  • Aperture
  • Focal length
40
Q

What dictates focal zone in single element array vs phased array / linear array?

A
41
Q

List 3 ways harmonic imaging improves image quality

A
42
Q

What characteristics of of harmonic frequencies are required for successful harmonic imaging?

A
43
Q

What is harmonic imaging best used for?

A
  • Abdo imaging: requires low freq to achieve penetration -> can switch to harmonic to improve quality of returning image
44
Q

List 3 types of doppler

A
45
Q

What 3 factors influence doppler effect?

A
46
Q

What is doppler shift frequency?

A
47
Q

What is the general doppler equation

A
48
Q

What is the doppler equation REARRANGED FOR BLOOD FLOW?

A
49
Q

What is the doppler shift equation AND rearranged for blood flow?

A
50
Q

Doppler example: What is the scatterer speed (cm/s) in the below example -> 2MHz incident freq, 0 doppler angle, shift 1.3kHz. Scatterer moving TOWARDS receiver

A

(1.3kHz x 1540m/s) / 2 x 2000kHz x cos 0)

= 0.5m/s

= 50cm/s

51
Q

DOPPLER SHIFT CALCULATION

A
52
Q

How does doppler shift relate mathmatically to

a) blood flow velocity
b) operating frequency

A

- PROPORTIONAL TO VELOCITY AND FREQ

Increase blood flow -> increase doppler shift

Increase operating frequency -> increase doppler shift

-

53
Q

What effect does increasing doppler angle have on doppler shift?

A

LARGER ANGLE = LESS SHIFT

Remember, maximum shift when angle = 0!!

54
Q

What is the peak veolocity of blood cells?

A

200cm/s

55
Q

What are preferred Doppler angles? Why?

A
56
Q

What are the 2 major groups of bioeffects to consider in US? What are their respective indices?

A
57
Q

Which US techniques are considered most likely to contribute to biological effects?

A
  • High power -> SPECTRAL DOPPLER,

Colour doppler and M-mode in the middle

Gray scale lowest

58
Q

What is GAIN? What is TIME GAIN COMPENSATION?

A
59
Q

Briefly, detail the components of the BEAM FORMER

A
60
Q

What is DYNAMIC RANGE?

A
61
Q

Briefly, detail the functions of the SIGNAL PROCESSOR

A
62
Q

What are the 4 MAJOR components of the US unit

A
63
Q

Briefly, detail the components / function of the IMAGE PROCESSOR

A
64
Q

In what way does US data change formats throughout the ultrasound unit?

A
65
Q

What is the difference between frame rate and refresh rate?

A
66
Q

Describe the different US display modes

A
67
Q

Describe manufacture of piezoelectric material. Which material? Process? Role of curie termperature?

A
68
Q

What affect does element thickness have on US beam?

A

Thickness determines OPERATING FREQUENCY

-> Thickness = 1/2 wavelength

69
Q

Briefly detail the DAMPING / BACKING BLOCK

A
70
Q

What is the role of the MATCHING LAYER

A
71
Q

Detail the affects of aperture and freq on near field length. What is aperture

A
72
Q

Detail how LINEAR / CURVED transducers work

A
73
Q

Detail the differences between sequential and phased array

A
74
Q

Describe the role of phasing in linear sequential array and phased array probes

A
75
Q

Briefly detail multifrequency transducers

A
76
Q

What are the three features that FRAME RATE is affected by?

A
77
Q

Detail the effects of FOV, DEPTH and LINE DENSITY on frame rate

A
78
Q

Detail COLOUR DOPPLER

A
79
Q

Detail POWER DOPPLER

A
80
Q

Detail TISSUE DOPPLER

A
81
Q

Describe different types of blood flow

A
82
Q

What does spectral broadening reflect in PW spectral doppler?

A
  • Disturbed or turbulent flow
83
Q

Briefly, detail what is plotted by spectral doppler. How do flow disturbances manifest?

A
84
Q

Briefly detail spectral analysis

A
85
Q

Briefly detail PW doppler

A
86
Q

Detail the calculation of 3 INDICES related to vascular resistance on spectral doppler

A
87
Q

Detail the bernoulli effect and modified bernoulli equation

A
88
Q

Briefy detail the differences in CEUS agents

A
89
Q

What feature of US units defines capacity for CONTRAST RESOLUTION?

A
  • Number of bits per pixel

Physics (10 decks)

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