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Medicine Year 1 Semester 1 - Part 2 > Ultrasound 1 & 2 > Flashcards

Ultrasound 1 & 2 Flashcards

1
Q

What is sound ?

A

A disturbance travelling through a medium; a series of interconnected particles.

Sound can be a longitudinal wave as well as a pressure wave

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2
Q

Longitudinal wave

A

Sound is a longitudinal wave that causes particles to vibrate (the particle motion is parallel to the direction of the energy).

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3
Q

Pressure wave

A

Sound is also, a type of pressure wave – molecules move close and further away, providing areas of higher and lower pressure.

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4
Q

Compression

A

High density region of particles.
Peaks

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5
Q

Rarefaction

A

Low density region of particles.
Troughs

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6
Q

Amplitude

A

Magnitude of the pressure change between peaks (compression) and trough (rarefaction).

Higher amplitude —> louder noise; related to power, measured in decibels (Db).

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7
Q

Wavelength

A

Distance between successive compressions/rarefactions.

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8
Q

Frequency

A

Number of sound waves per second; Hertz (Hz).

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9
Q

1Hz

A

1 wave per second

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10
Q

What is frequency in relation to wavelength ?

A

Inversely proportional to wavelength (λ) i.e. if wavelength decreases then frequency increases and vice versa.

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11
Q

What is frequency in relation to speed ?

A

Frequency is proportional to speed (c).

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12
Q

Audible human range

A

20 Hz to 20 kHz

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13
Q

Speed of a vibration

A

Speed refers the distance travelled of a vibration wave per unit time (i.e. how fast).

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14
Q

What does speed depend on ?

A

Depends on the properties of the medium (gas < liquid < solid).

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15
Q

What does speed relate to ?

A

Acoustic impedance

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16
Q

Frequency of a vibration

A

The number of vibrations an individual particle makes per unit time (i.e. how often)

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17
Q

Ultrasound

A

Ultrasound refers to frequencies >20kHz
(above human audible range).

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18
Q

MHz

A

Megahertz
10^6 Hz

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19
Q

GHz

A

Gigahertz
10^9 Hz

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20
Q

What are the medical ultrasound operating values ?

A

Medical ultrasound typically operates at 1 to 15MHz .

(~50 to 750x higher frequency than the maximal human hearing range)

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21
Q

What are some considerations for ultrasound ?

A

Resolution
Penetration

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22
Q

What is resolution ?

A

Sharpness of image

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23
Q

What is penetration ?

A

Depth of image

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24
Q

What does resolution relate to ?

A

Related to frequency.

i.e. when wavelengths of 1mm used, structures smaller than 1mm appear blurred (the waves don’t hit the target structure)

Therefore, higher frequency = higher resolution

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25
Q

How is resolution related to frequency ?

A

Higher frequency = Higher resolution

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26
Q

What is penetration related to ?

A

Inversely related to resolution
(i.e. higher resolution —> reduced penetration)

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27
Q

How is penetration related to resolution ?

A

Higher resolution = Reduced penetration

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28
Q

Results of lower frequency (MHz)

A

Increased penetration
Decreased resolution

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29
Q

Results of higher frequency (MHz)

A

Decreased penetration
increased resolution

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30
Q

States the 4 components that resolution is divided into

A

Axial
Lateral
Elevational
Temporal

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31
Q

Axial (vertical) component of resolution

A

The ability to differentiate objects along axis of ultrasound beam (depends on frequency).

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32
Q

What does the axial component of resolution depend on ?

A

Frequency

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33
Q

Lateral (horizontal) component of resolution

A

The ability to differentiate objects perpendicular to beam. (depends on width of beam at given depth)

  • Aim for the focal zone (i.e. area of highest beam intensity)
  • Ultrasound beams have a curved shape
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34
Q

Focal zone

A

Area of highest beam intensity

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35
Q

Elevational component of resolution

A

Fixed property of the transducer
(the thickness of the beam)

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36
Q

Temporal component of resolution

A

Resolution of moving structures

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37
Q

Piezoelectric effect

A

Piezoelectric Effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress.

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38
Q

What is emitted by piezoelectric material ?

A

Sound waves are emitted by piezoelectric material (crystals) contained within ultrasound transducers.

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39
Q

Describe the piezoelectric effect

A

When alternating electrical current is applied, the piezoelectric material oscillates, in response to mechanical strain.

This produces vibrations and sound waves are generated.

The beam then penetrates the tissues, with some waves being reflected.

The electrical amplitude is analysed and the amplitude of the returning signal is displayed as a grey-scale image.

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40
Q

Direct piezoelectric effect

A

When mechanical strain results in electric signal, it is known as direct piezoelectric effect.

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41
Q

Reverse piezoelectric effect

A

When electric signal results in mechanical strain, it is known as reverse piezoelectric effect.

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42
Q

What does stronger signals result in ?

A

Stronger signals result in a brighter picture.

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43
Q

What is deflection of sound tissues ?

A

Reflection + Refraction + Scattering = Deflection

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44
Q

What is meant by acoustic impedance ?

A

Acoustic impedance is the resistance to sound passing through.

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45
Q

Explanation of acoustic impedance

A

When moving from one type or tissue to another (interface) greater differences in acoustic impedance lead to greater reflection of the sound waves.

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46
Q

Greater differences in acoustic impedance results

A

Greater reflection of sound waves.

At air-tissue interfaces there is greater scatter of sound waves

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47
Q

High acoustic impedance meaining

A

High resistance to sound passing through

e.g. Air and Bone both have high acoustic impedance

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48
Q

What is attenuation ?

A

As sound travels through tissues, energy is lost, intensity is diminished.

This is mainly due to absorption, but also deflection and divergence.

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49
Q

What is attenuation dependent on ?

A

Attenuation is dependent on :

  • frequency of wave
  • distance travelled
  • attenuation coefficient of tissue.
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50
Q

What is the attenuation coefficient of air ?

A

7.50

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51
Q

What is the attenuation coefficient of bone ?

A

15.00

52
Q

What is meant by absorption ? (in relation to attenuation)

A

Absorption is sound wave energy transferred to heat energy in the tissue.

Higher Frequency ; Increased absorption therefore decreased penetration.

53
Q

Monitor

A

Displays images

54
Q

Ultrasound Unit (US Unit)

A

Processes ultrasound images

55
Q

Control Panel

A

Knobs and controls

56
Q

Transducer

A

Produces and receives ultrasound waves

57
Q

Name the parts of the ultrasound machine

A

Monitor
Ultrasound unit
Control panel
Transducer

58
Q

State the types of transducer (ultrasound probes)

A

Linear
Curvilinear
Phased array
Intracavitary

59
Q

Describe features of linear transducers

A

Frequency range : 5-15 MHz
Imaging depth : 9cm

High frequency
Low depth of imaging
Flat footprint produces undistorted

60
Q

HFL38/13-6 meaning

A

13-6 MHz Range + 38mm footprint

61
Q

Describe features of curvilinear transducers

A

Frequency range : 2-5 MHz
Imaging depth : 30cm

Low frequency probe
Low image resolution
Good depth of imaging (e.g. abdominal scan)
Slight distortion of images

62
Q

What are smaller curvilinear probes used for ?

A

Intraluminal scanning

63
Q

Describe features of phased array transducers

A

Frequency range : 1-5 MHz
Imaging depth : 35cm

Large scanning area
Large depth
Good resolution
Small footprint

64
Q

Where are the sound waves generated in phased away probes ?

A

From the centre of the footprint, this allows a small probe but a large scanning area and depth.

65
Q

Advantage of small footprint of phased away probe

A

The probe can scan in small or awkward areas.

e.g. trans-thoracic echocardiography (between ribs)

66
Q

Describe features of intracavitary transducers

A

Frequency range : 5-8 MHz
Imaging depth : 13cm

67
Q

Advantage of the intraluminal probe
(intracavitary transducer)

A

Places the probe close to area to be imaged.

Overcomes poor imaging resulting from overlying structures (e.g. adipose tissue)

Allows use of high-frequency (higher resolution images)

68
Q

Uses of the intraluminal probe

A

Endovaginal
Endorectal
Other (e.g. on endoscopes)

69
Q

What are applications of linear transducers ?

A

Arteries/veins
Pleura
Skin/soft tissue
Testicles/hernia
Eyes
Thyroid
Lymph nodes
Nerves

70
Q

What are applications of curvilinear transducers ?

A

Gallbladder
Liver
Kidney
Spleen
Bladder
Abdominal aorta
Abdominal free fluid
Uterus/ovaries
Lumbar puncture

71
Q

What are applications of phased array transducers ?

A

Heart
Inferior Vena Cava
Lungs
Pleura
Abdomen
Transcranial doppler

72
Q

What are applications of intracavitary transducers ?

A

Uterus/ovaries
Pharynx

73
Q

Imaging modes

A

3 main modalities to cover;

  • 2D mode (aka Brightness or B-mode)
  • Motion mode (M-mode)
  • Doppler mode (D-mode)
74
Q

What is the most common imaging mode ?

A

2D mode : B-mode : Brightness mode

75
Q

Echogenicity

A

Brightness

76
Q

What affects echogenicity ?

A

The brightness of a structure depends on intensity (amplitude) of reflected signal

77
Q

Anechoic

A

Structures transmitting all waves (without reflection)
Black in colour

(anything fluid filled)
e.g. blood, bile, urine

78
Q

Hypoechoic

A

Structures reflecting less waves than surroundings.
Less dense
Dark coloured

e.g. kidneys

79
Q

Hyperechoic

A

Structures reflecting more waves than surroundings (may result in ‘shadowing’)
More dense
Brightly coloured

e.g. diaphragm

80
Q

Isoechoic

A

Simliar waves to surroundings

81
Q

Motion mode (M-mode)

A

Analyses movements of structures over time
(e.g. dimensions of cavities over time - cardiac, vascular, pleura)

Scan line selected on a 2D scan using an M-mode cursor - the target structure

A single axis beam emitted along a scan line and movements plotted.

82
Q

What is the doppler effect ?

A

The doppler effect is a shift in frequency of sound waves due to motion between the source and observer.

e.g. Ambulance sirens will appear higher pitched moving towards you and lower pitches when moving away.

83
Q

Dopler sub-modes

A

Spectral (pulsed/continuous)
Colour flow
POwer

84
Q

Spectral doppler

A

The doppler effect represented graphically;

If the frequency shifts :

-Above baseline - Indicates flow towards the transducer
-At baseline - Indicates perpendicular flow to transducer

-Below the baseline - Indicates flow away from the transducer

85
Q

Pulsed wave spectral doppler

A

Transducer emits pulsed sound waves in cycles, measured at precise location.

86
Q

Continuous wave spectral doppler

A

Measures blood flow velocity along an entire beam. (instead of specific location)

87
Q

Colour flow doppler

A

Colour coded doppler shifts superimposed on a 2D image (same principles as pulsed-wave)

88
Q

What does the colour in the colour flow doppler correspond to ?

A

Colour corresponds to direction and velocity of flow.

89
Q

What do the colours in colour flow doppler mean ?

A

Blue - away from transducer (longer wavelengths)
Red - towards transducer (shorter wavelengths)

90
Q

Power flow doppler

A

Similar to colour flow but no directionality.

Analyses only amplitude of returning echoes.
Level of brightness is proportional to magnitude of flow.

91
Q

Advantages of power flow doppler over colour flow doppler

A

Power flow is :

  • Less angle dependent
  • No aliasing
92
Q

Disadvantages of power flow doppler compared to colour flow

A

No directional information (less useful for cardiac imaging)

More susceptible to artifacts

93
Q

What are ultrasound artefacts ?

A

False images, or parts of images, that do not represent the true anatomical structure.

  • Can be used for diagnosing pathology
94
Q

Acoustic shadowing result

A

You will not be able to see structures underneath bone.

95
Q

What is acoustic shadowing ?

A

Seen distal to high attenuating structures

96
Q

High attenuating structures

A

Reflect, Scatter or Absorb majority of sound waves.

Distally amplitude of sound waves significantly reduces, few echoes return causing a shadow to form.

97
Q

Acoustic enhancement

A

Commonly seen deep to fluid-filled structures

98
Q

What is acoustic shadowing ?

A

Sound travels through low-attenuating fluid-filled structure (unimpeded) resulting in the intensity of the sound waves preserved when hitting deeper structures

Creates a uniformly brighter, hyperechoic appearance of deep tissue (e.g. full bladder, gallbladder and large blood vessels)

99
Q

Anisotropy

A

Exhibition of properties/structures with different values when measured at different directions.

100
Q

Correct orientation of the probe

A

Saggital/coronal plane : Marker to head (cephalic)

Transverse plane : Marker to the right side

Superficial structures appear at the top of the screen

101
Q

Name the 4 manoeuvres of the probe

A

Sliding
Rotating
Tilting
Rocking

102
Q

What is the sliding manoeuvre used for ?

A

Identify structures / avoid ribs

103
Q

What is the rotating manoeuvre used for ?

A

Alignment of vessels

104
Q

What is the tilting manoeuvre used for ?

A

Serial cross-sectioning, anisotropy

105
Q

What is the rocking manoeuvre used for ?

A

Centering of deep image

106
Q

What does reflection and propagation of sound through tissues depend on ?

A

Attenuation
Acoustic impendance

107
Q

Benefits of ultrasound

A

Good safety record
Non-ionising radiation
Non-invasive
Painless
Portable
Relatively inexpensive

108
Q

Risks of ultrasound

A

Potential bio-effects
- Thermal
- Cavitating

Sensitive tissues :

Embryo <8weeks
Neonatal/foetal head/ spine/ eye (all ages)

Long term effects are unknown

109
Q

ALARA principle

A

As low as reasonably achievable

Used to reduce the risk of harm from potential bio effects of ultrasound.

110
Q

How is ultrasound used in clinical medicine ?

A

Treatment
Diagnostics
Procedures

111
Q

Describe uses of ultrasound in treatment

A

Kidney stones
Prostate cancer
Soft tissue injuries

112
Q

Lithotripsy

A

Extracorporeal shock wave lithotripsy is a technique for treating stones in the kidney and ureter that does not require surgery.

Instead, high energy shock waves are passed through the body and used to break stones into pieces as small as grains of sand.

113
Q

Describe uses of ultrasound in diagnostics

A

Comprehensive
Focussed = POCUS

114
Q

POCUS

A

Point Of Care UltraSonography

  • Goal directed
  • Bedside
  • To answer a specific diagnostic question or to guide an invasive procedure
115
Q

Comprehensive examination facts

A

Comprehensive involves thorough evaluation of an entire anatomical region or organ.

Performed by specialists
(specialised radiographers, radiologists, cardiologists)

Often performed in the radiology department

Non-emergency situations

Lengthly process can take days :
Request –> Perform –> Interpret –> Report

Generates a detailed report on the area examined to make a diagnosis or guide clinical decision making.

116
Q

POCUS examination facts

A

Usually single organ examination

Performed by non-radiologists - doctors trained in specific POCUS examinations related to scope of practice.

Performed at bedside

Can be used in emergency or life-threatning situations.

Takes minutes

Used to answer a specific question or ‘Rule in/out’ a diagnosis.

Can be used to guide invasive procedures

117
Q

Steps of clinical examination

A

Observation
Palpation
Auscultation
Ultrasound

118
Q

POCUS benefits

A

Patents can stay in the department for ongoing treatment

Can provide rapid answer to clinical questions to aid faster decision making

Portable around clinical area

Improves outcomes of invasive procedures

119
Q

POCUS limitations

A

Operator dependent
Familiarity with equipment

Limited, focused information

Can only provide answers to simple clinical questions

Availability of ultrasound machines

Patient characteristic considerations

120
Q

Use of ultrasounds in procedures

A

Biopsy
Vascular access

121
Q

Pericardiocentesis

A

Pericardial fluid

122
Q

Lumbar puncture

A

Cerebrospinal fluid

123
Q

Thoracocentesis

A

Pleural fluid

124
Q

Paracentesis

A

Peritoneal fluid

125
Q

Arthrocentesis

A

Synovial fluid

126
Q

Vascular access

A

Cannulation
Central venous catheter

Medicine Year 1 Semester 1 - Part 2 (37 decks)

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