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Westmead Physics > Ultrasound > Flashcards

Ultrasound Flashcards

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1
Q

How many wave cycles are usually transmitted from an ultrasound probe each time?

A

3-5

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2
Q

What is the rough speed of US

A

1500m/s

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3
Q

What are the advantages/ disadvantages of higher frequency ultrasounds?

A

more details,

a lot quicker attenuation, so can’t see deep

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4
Q

Unit of measurement for ultrasound attenuation?

A

dB/cm/MHz

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5
Q

What causes a reflection of US?

A

an interface between two different tissues

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6
Q

What are some highly reflective substances in humans?

A

gas, bone, plastic

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7
Q

What’s the difference between reflection and scattering in Ultrasound?

A

Scattering happens with very small objects only, unlike reflection the energy goes in all directions

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8
Q

What is PRF in ultrasound?

A

Pulse repetition frequency

How often the probe can send out pulses of ultrasound

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9
Q

What is speckle in US?

A

The echoes from individual scattering objects. Causes the granular appearance of USS.

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10
Q

What is aperture in US production?

A

the area of the probe face used to create the US

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11
Q

What factors can narrow an US beam?

A

higher frequency US

larger aperture

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12
Q

How does electronic US focusing work?

A

US waves from the sides start before waves in the centre, they all add together and should, therefore, create a narrowest beam around the focus area.

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13
Q

What is dynamic receive focusing in US?

A

the US receiver constantly adjusting the focus because it knows how deep the ultrasounds are coming from based on speed and time

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14
Q

What are sidelobes in US?

A

beam intensity peaks to either side of the main beam.

Due to constructive interference of the US waves from different transducer parts.

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15
Q

Is axial or longitudinal resolution better in US?

A

axial (much better, 3x often)

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16
Q

Why is longitudinal resolution limited in US?

A

smearing due to the beam not being perfectly narrow

17
Q

What is dynamic range compression?

A

Compresses the range of ultrasound echoes received into a range that can be displayed on the screen and appreciated by humans

18
Q

Why is dynamic range compression needed?

A

As there is a huge range of signal that can return to the US probe, and we can’t appreciate it all visually.

The more intense stuff is pretty useless.

19
Q

Why is quantitive information regarding highly echogenic tissues not diagnostically useful on US?

A

As the signal strength is related to the angle the object makes with the probe, as these objects are speculated (mirror-like)

20
Q

What are the disadvantages of HIGH dynamic range ultrasound

A
  • Little differentiation of tissue type

- artefact echoes more visible

21
Q

What are the disadvantages of LOW dynamic range ultrasound

A
  • Areas where the signal drops out

- Coarser texture

22
Q

What does a scan converter do in US?

A
  1. Takes echo information in real-time and puts it in the geometrically correct area of memory,
  2. fill in any blank pixels with guesses
23
Q

Examples of PRE-processing in US:

A

○ Zoom
○ Depth
○ Persistence
○ Compound imaging

24
Q

Examples of POST-processing in US:

A
  • Post processing zoom (not as good)
    • Colour mapping (B-mode)
    • measurements
25
Q

What are the assumptions that occur in US calculations?

A
  • Propagation speed = 1540m/S
    • Narrow beam
    • US travels in straight line, directly from and back to the transducer
    • Uniform attenuation
26
Q

What common tissue has notably different US travel speed?

Does it travel faster or slower?

A

Fat,

it’s slower (1450m/s vs 1540m/s normally)

27
Q

Why do depth errors occur in US?

A

As ultrasound beams travel at different speeds through different tissues, but the machine isn’t able to adjust for this, at assumes they always travel at the same speed (1540m/s)

28
Q

What the doppler effect in US?

A

When US round-path distance of the ultrasound changes with time

Due to moving scatterers such as blood vessels

29
Q

Ways to display doppler effect on US

A

○ Pulsed doppler
○ Colour doppler
○ Cw doppler

30
Q

What is cavitation in US?

A

Small as bubbles oscillate in ultrasound field, in some conditions they can grow then collapse creating 1000 degree temperature areas

Westmead Physics (17 decks)

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