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Physics > US > Flashcards

US Flashcards

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
How does dampening relate to bandwidth and Q factor?
- Increase dampening: DECREASE SPL INCREASE BANDWIDTH DECREASED Q FACTOR
26
Define range and how distances are calculated by US
27
What factors increase acoustic impedance?
- Increased density - Increased propagation speeds THINK ABOUT THE EQUATION!
28
What is the speed of sound in ST?
1540m/s (1.54 mm/microsecond)
29
For a reflector at 5cm depth, calculate pulse round trip time
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
30
What is the rule that can help with pulse round trip time?
- 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
31
TABLE
32
Define wavelength, propagation speed and frequency. How do they relate?
33
A 5 MHz beam travels from soft tissue into fat. Calculate wavelength in each medium and determine % wavelength change
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!!**
34
What is the speed of sound in ST and FAT?
ST = 1540m/s Fat = 1450m/s
35
How do spatial resolution and attenuation relate to wavlength and frequency?
Resolution -\> increases with smaller wavelength (higher frequency) Attenuation -\> Increases with smaller wavelength (higher frequency)
36
TABLE
37
What features determine size of near field?
- **Unfocused single array:** Tranducer diameter Frequency **- Multiple element array** Effectrive diameter (excitation of groups of elements) INCREASES with increasing width or frequency ("Aperture")
38
What factors affect beam divergence in the far zone?
**APERTURE!** - Frequency: Higher frequency, less divergence - Beam width: Larger width, less divergence
39
List 3 things that can create beam focusing, and 3 things that limit beam focusing
Cause: - Curved elements - Lens - Phasing Limiters: - Wavelength - Aperture - Focal length
40
What dictates focal zone in single element array vs phased array / linear array?
41
List 3 ways harmonic imaging improves image quality
42
What characteristics of of harmonic frequencies are required for successful harmonic imaging?
43
What is harmonic imaging best used for?
- Abdo imaging: requires low freq to achieve penetration -\> can switch to harmonic to improve quality of returning image
44
List 3 types of doppler
45
What 3 factors influence doppler effect?
46
What is doppler shift frequency?
47
What is the general doppler equation
48
What is the doppler equation REARRANGED FOR BLOOD FLOW?
49
What is the doppler shift equation AND rearranged for blood flow?
50
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
(1.3kHz x 1540m/s) / 2 x 2000kHz x cos 0) = 0.5m/s = 50cm/s
51
DOPPLER SHIFT CALCULATION
52
How does doppler shift relate mathmatically to a) blood flow velocity b) operating frequency
**- PROPORTIONAL TO VELOCITY AND FREQ** Increase blood flow -\> increase doppler shift Increase operating frequency -\> increase doppler shift -
53
What effect does increasing doppler angle have on doppler shift?
LARGER ANGLE = LESS SHIFT Remember, maximum shift when angle = 0!!
54
What is the peak veolocity of blood cells?
**200cm/s**
55
What are preferred Doppler angles? Why?
56
What are the 2 major groups of bioeffects to consider in US? What are their respective indices?
57
Which US techniques are considered most likely to contribute to biological effects?
- High power -\> **SPECTRAL DOPPLER,** Colour doppler and M-mode in the middle Gray scale lowest
58
What is GAIN? What is TIME GAIN COMPENSATION?
59
Briefly, detail the components of the BEAM FORMER
60
What is DYNAMIC RANGE?
61
Briefly, detail the functions of the SIGNAL PROCESSOR
62
What are the 4 MAJOR components of the US unit
63
Briefly, detail the components / function of the IMAGE PROCESSOR
64
In what way does US data change formats throughout the ultrasound unit?
65
What is the difference between frame rate and refresh rate?
66
Describe the different US display modes
67
Describe manufacture of piezoelectric material. Which material? Process? Role of curie termperature?
68
What affect does element thickness have on US beam?
Thickness determines OPERATING FREQUENCY -\> Thickness = 1/2 wavelength
69
Briefly detail the DAMPING / BACKING BLOCK
70
What is the role of the MATCHING LAYER
71
Detail the affects of aperture and freq on near field length. What is aperture
72
Detail how LINEAR / CURVED transducers work
73
Detail the differences between sequential and phased array
74
Describe the role of phasing in linear sequential array and phased array probes
75
Briefly detail multifrequency transducers
76
What are the three features that FRAME RATE is affected by?
77
Detail the effects of FOV, DEPTH and LINE DENSITY on frame rate
78
Detail COLOUR DOPPLER
79
Detail POWER DOPPLER
80
Detail TISSUE DOPPLER
81
Describe different types of blood flow
82
What does spectral broadening reflect in PW spectral doppler?
- Disturbed or turbulent flow
83
Briefly, detail what is plotted by spectral doppler. How do flow disturbances manifest?
84
Briefly detail spectral analysis
85
Briefly detail PW doppler
86
Detail the calculation of 3 INDICES related to vascular resistance on spectral doppler
87
Detail the bernoulli effect and modified bernoulli equation
88
Briefy detail the differences in CEUS agents
89
What feature of US units defines capacity for CONTRAST RESOLUTION?
- Number of bits per pixel

Physics (10 decks)

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