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CSH059 > Ultrasound > Flashcards

Ultrasound Flashcards

1
Q

how is ultrasound used in RT

A
  • as a diagnostic tool
  • image guidance
    • interfraction motion estimation in prostate and breast
    • gynaecological application, placement of brachytherapy
    • localisation tool (eg. ovaries)
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2
Q

initial diagnosis of what tumours are ultrasound used

A

liver
pancreas
kidney
breast
prostate

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3
Q

electromagnetic waves

A
  • travel at the speed of light
  • no medium is required for propagation
  • distinguished by energy, frequency and wavelength
    • eg. light and x-rays are electromagnetic waves
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4
Q

mechanical waves

A
  • defined as the propagation of energy through a medium by cyclic pressure variations
  • need deformable elastic medium for propagation (such as air, water, soft tissue)
    • ultrasound propagates by mechanical waves
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5
Q

two types of mechanical waves

A
  • transverse
    • the particle motion in the medium is 90 degrees to the direction of the wave
  • longitudinal waves
    • the particle motion in the medium is in the same plane as the direction of the wave
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6
Q

pulse echo sequence

A
  • once a pulse has been sent into tissue, the transducer is set to receive mode
  • the returned echo is converted into an electrical voltage
  • the time from pulse transmission to echo receive can be accurately measured, ant this is used to calculate the interface depth
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7
Q

interface depth formula

A

d=vt/2

d is the depth of reflector (in m)
v is the velocity of sound (1540 m.s.)
t is the roundtrip time of the pulse

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8
Q

different transducer types

A
  • curvilinear
    • very good for abdominal structures + obsetrics
  • linear array
    • used in vascular (arteries and veins), lens and retina, musculoskeletal
  • intracavity
    • gynae, uterus and ovaries
  • phased array
    • cardiac
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9
Q

what are the different directions the transducer can move in

A

in 3 planes - X, Y and Z plane

X plane = sweep and fan
Y plane = slide and rock
Z plane = compression and rotation

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10
Q

what are the 4 different types of resolution

A

spatial
contrast
temporal
colour

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11
Q

what is resolution

A

the degree of detail that structures can be seen on images

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12
Q

spatial resolution

A

the ability to differentiate small structures on a B mode image

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13
Q

two types of spatial resolution

A

axial and lateral

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14
Q

what affects spatial resolution

A

beam characteristics
line density (which affects lateral resolution
resolution of the viewing monitor

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15
Q

axial resolution

A

the closest distance between two structures can be along the beam axis and is differentiated as two entities

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16
Q

lateral resolution

A

the closet distance between two structures can be at 90 degrees across the axis of the beam and can be seen as different entities

17
Q

focal zone + its affect on the beam

A

considered the beams ‘waist’

any given echo will give rise to a stronger echo when it lies within the focal zone because the beam is at its highest intensity at the centre of the beam

the beam width is also narrowest at the focus, therefore lateral resolution is improved

18
Q

contrast resolution + depends on

A

the ability to differentiate tissues of different echogenicity

depends on
- the amount of background noise and backscatter interference in the image
- slice thickness
- inherent characteristics of the electronics of the machine and transducer construction

19
Q

what are the terms used to describe echogenicity

A
  • anechoic (echolucent or sonolucent) = absence of echoes
  • hypoechoic (echopenic) = low level echo
  • hyperechoic (echogenic) = high echo
20
Q

what are the terms used to describe echotexture

A
  • fine or coarse
  • homogenous = very even pattern
  • heterogenous = mixed pattern
21
Q

temporal resolution

A

ability to resolve rapidly moving structures - dependent on the time frame

high frame rates are required for increased temporal resolution

22
Q

colour resolution

A

a term used to describe the spatial resolution of the Doppler colour display when defining moving substances (usually blood)

how well are colour displayed to demonstrate moving substances (eg blood)

23
Q

Doppler effect

A
  • assumed change in frequency that occurs due to relative motion between
    • wave source
    • receiver
    • reflector of the wave
24
Q

doppler shift

A

difference between received and transmitted frequencies due to motion of blood flow relative to beam

change in F = frequency received - frequency transmitted

25
Q

received frequency dependent on

A

transducer frequency
speed of sound
velocity of blood flow
intercept angle

26
Q

overall gain

A

the amount of gain/brightness applied to the returning echoes in an image

increasing gain too much will add noise, and decreasing too far can potentially lose information

27
Q

time gain compensation (TGC) or depth gain compensation (DGC)

A

is the gain applied according to the depth or attenuation of the images as ultrasound travels through it

28
Q

basic B-mode controls

A

frequency
focal zone
gain controls
depth

29
Q

grayscale QA phantom

A

used to test a range of imaging parameters on an ultrasound system, including the accuracy of measurements and the limits of system resolution

30
Q

pros of ultrasound in RT

A

non ionising
cheaper, fast
mobile
more appealing for claustrophobic patients
can be used for pregnant women

31
Q

cons of ultrasound in RT

A

highly operator dependent.
possible allergy to the gel
not user friendly, need experience
difficult to visualise bone
low resolution compared to MRI or CT
air or gas blocks visualisation

32
Q

what are the basic B-mode controls

A

gain and TCG
frequency
focal zone
depth

33
Q

spatial pulse length

A

the length of time that an ultrasound pulse occupies in space or the length of the pulse we send out

axial resolution is directly related to SPL

34
Q

spatial pulse length is affected by

A

the frequency
- higher frequency = shorter wavelength = shorter SPL

the transducer type
- better damping = fewer cycles = shorter SPL

35
Q

SPL formula + how it relates to axial resolution

A

SPL = number of cycles x wavelength

AR = 1/2 SPL

CSH059 (7 decks)

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