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Physics > Imaging > Flashcards

Imaging Flashcards

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1
Q

what is image registration

A

process of spatially aligning two images together

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2
Q

what info does CT provide?

A

great anatomical detail, enhanced with contrast

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3
Q

what info does RNI provide

A

great physiological info, but poor anatomical info, so is used alongside other modalities

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4
Q

what is the role of imaging

A

that the target volume is being treated

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5
Q

what info does MRI provide

A

greater anatomical details, enhanced with contrast, with an increased use

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6
Q

what info does ultrasound provide

A

great anatomical detail for soft tissues

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7
Q

why are images gathered

A

to avoid errors
- systematic = QA program
- random = imaging, QA programme and education

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8
Q

why is registration important

A
  • follow up studies
  • inflammatory disease diagnosis
  • RT planning
  • neurological disorders
  • RT portal film comparison with ref image
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8
Q

why is registration important

A
  • follow up studies
  • inflammatory disease diagnosis
  • RT planning
  • neurological disorders
  • RT portal film comparison with ref image
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9
Q

what is a random error

A

a deviation which can vary in direction and magnitude for each delivered fraction. these are not inherent within the process, normally only occur once

<2mm

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10
Q

what is a systematic error

A

an error which is introduced at the beginning of treatment and carried throughout the whole treatment. The deviation occurs in the same direction and is of similar magnitude for each fraction throughout the treatment course.
<5mm

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11
Q

what is a pixel

A

2D space

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12
Q

what is a voxel

A

3D space

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13
Q

what are fiducial markers

A

markers which are found internally or outside the treatment couch, which act as a reference point. They are used in image registration

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14
Q

what is localisation

A

location of where it is in reference with other body parts. it can act as a reference marker outside the body

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15
Q

what position is the same as the treatment position

A

CT position

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16
Q

what are some equipment adaptations

A
  • couch is flat and not dish shaped
  • treatment position, otherwise it could lead to geographical miss
  • accessory equipment must attach directly to the couch accurately
17
Q

what is a simulator

A

it is similar to the treatment couch, which is isocentrically mounted, but it doesn’t visualise soft tissue, all tissue looks the same

18
Q

what is the ideal equipment

A
  • treatment position
  • anatomical + functional info
  • minimal/no radiation dose
  • localisation and position of where the tumour is active
  • good image quality
  • information of x-ray absorption
19
Q

why are radio-opaque markers used

A

they are inserted in the body, which help with the alignment so that the patient is in the same position

20
Q

what is contrast

A

it is the state of being strikingly different from something else in juxtaposition or close association. There is a difference in density
bone = white, air = black, soft tissue = grey

21
Q

what is the density of darker images

A

greater density

22
Q

what energy is used in electrons

A

MeV

23
Q

what is a reference image

A

a selected standard image used against all online images, MV images are taken prior treatment

24
Q

what is geographical miss

A

it is when the beam placement is wrong, so the target is missed and normal tissue is treatment

25
Q

what is a radiation map

A

it is a representation of a patients internal anatomy, in which the map interacts with the recording system converting to light. As more light reaches the system, the more blackening occurs

26
Q

how is detailed controlled

A

by the number of pixels, each pixel represents a ‘colour’ (a shade of grey which is matched with the number of IE which it holds)

27
Q

what does magnification do to an image

A

stretches the pixels

28
Q

what is CR

A

Computed radiography
- x-ray images are captured on a cassette which contain a phobostimuble phosphor imaging plate
- the x-ray is trapped and the image is extracted from the IP through a laser and then digitised

29
Q

what is DRR

A

Direct Digital Radiograph
- contains a conversion layer and an electronic readout layer, x-rays are converted into light and then electrical charges. Its transmitted out of the detector using algorithms to produce an image

30
Q

why is a Kodak film useful

A

at high dose ranges within relative dosimetry

31
Q

what are the two ways of creating images

A

passive: reflects a fluorescent light through the crystals projecting an image, it has a time lag so there is a low viewing angle and reduced brightness
active: uses a LED containing brighter lights, superior contrast and resolution with angles similar to TV monitors

32
Q

what happens to the crystals

A

they can shape allowing a variable amount of light through

33
Q

do darker regions have more or less absorption

A

more

34
Q

what does a HL7 ensure

A

that textual info is encoded in a way that only other computers can decode and decipher strings of text

35
Q

what 5 RT objects has a DICOM specified

A
  • RT image: DRR, portal + simulator images
  • RT plan: contains geometric and dosimetric data for external beam and brachytherapy
  • RTSS: anatomical info
  • RT dose: dose data
  • RT treatment record: data from sessions and records
36
Q

why are digital images useful

A

they allow for extraction of info or correct original data. The grey values are represented in the DRR panel when the image is generated - system fidelity

37
Q

what is a method needed for:

A
  • directing radiation through the body
  • recording the radiation patterns
  • converting the patterns accurately
  • radiation into light - an image
38
Q

what are artefacts

A

a structure which doesn’t directly correlate with the actual tissue

39
Q

what are the causes of artefacts

A
  • acoustic properties of tissue
  • improper operation of equipment
  • malfunctioning or faulty equipment
40
Q

where are artefacts common

A
  • reverberation
  • resolution
  • posterior acoustic shadow
  • posterior cystic enhancement
  • mirror image
  • edge artefact

Physics (25 decks)

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