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3rd year - module 6 > Radiology > Flashcards

Radiology Flashcards

1
Q

What is the basic principle of CBCT ionising radiation?

A

conical/pyramidal X-ray beam and square digital detector rotate around head (no more than one full rotation), captures many 2D images which are reconstructed into a 3D image

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2
Q

How is a patient usually positioned in a CBCT machine?

A

usually either standing or sitting
rarely supine

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3
Q

What are the horizontal and vertical planes of CBCT head positioning based upon?

A

horizontal - frankfort plane (ie head level with ground)
vertical - midsaggital plane

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4
Q

What are the advantages of CBCT over plain radiography?

A
  • no superimposition
  • ability to view subject from any angle
  • no magnification/distortion
  • allows 3D reconstruction
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5
Q

What are the disadvantages of CBCT compared to plain radiography?

A
  • increased radiation dose
  • lower spatial resolution
  • susceptible to artefacts
  • expensive equipment
  • imaged more complicated to interpret
  • requires additional training
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6
Q

What are the benefits of a CBCT compared to conventional CT scan?

A
  • lower radiation dose
  • potential for sharper images
  • cheaper
  • smaller footprint
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7
Q

What are the main benefits of conventional CT compared to CBCT?

A
  • able to differentiate soft tissues better
  • “cleaner” images
  • large field of view possible
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8
Q

What are the common uses of CBCT in dentistry?

A
  • relationship btwn M3M and IANC prior to intervention
  • alveolar bone dimensions to plan implant placement
  • visualising complex root morphology for endo
  • investigating external root resorption next to impacted teeth
  • assessing large cystic jaw lesions and involvement of anatomical structures
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9
Q

What are the three common orthogonal planes?

A
  • axial (above or below)
  • sagittal (split down middle into L and R)
  • coronal (front or back, shoulder to shoulder)
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10
Q

What are the uses of 3D volume reconstruction?

A
  • help clinician picture extent/shape of disease
  • can be informative teaching aid for patient
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11
Q

What are the drawbacks of 3D volume reconstruction?

A

it is a modified reconstruction of the data and so can create misleading images - particularly poor at showing thin bone

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12
Q

What is the field of view?

A

size of the captured volume of data
decision based on clinical case

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13
Q

What does an increased FOV also increase?

A

increases radiation dose, number of tissues irradiated an increased scatter

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14
Q

What is a voxel?

A

3D pixel

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15
Q

What does voxel size impact?

A

image resolution

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16
Q

What does a decreased voxel size do?

A

leads to increased radiation dose and scan time

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17
Q

What imaging factor choices would you make for an endodontic case?

A

FOV as small as possible unless large apical pathology
small voxel size to see canals in detail

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18
Q

What imaging factor choices would you make for an implant treatment planning case?

A

FOV depends on number/position of implants
larger voxel size (fine detail not as necessary)

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19
Q

What factors can impact radiation dose?

A

equipment, FOV, position of FOV, voxel size

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20
Q

Dento-alveolar CBCT is roughly what multiplication of the radiation dose of a panoramic radiograph?

A

2-3x dose of panoramic radiograph

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21
Q

What are artefacts?

A

visualised structures that were not present in object investigated
most can be avoided

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22
Q

What are the two main types of artefacts?

A

1) movement artefacts
2) streak artefacts

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23
Q

What is a movement artefact and how does it occur?

A

occurs if patient not completely still during full exposure
leads to general blurriness or extra contours

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24
Q

How are movement artefacts avoided?

A

reduced using fixation aids - chin rest, head strap etc

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25
Q

What are streak artefacts caused by and what are their main issues?

A
  • most notably caused by high-attenuation objects, primarily metals e.g. amalgam
  • can prevent caries assessment adjacent to restorations
  • can prevent assessment of perforations/missed canals in root treated teeth
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26
Q

What are the contraindications for CBCT?

A
  • if plain radiographs are sufficient
  • pathology requiring soft tissue visualisation eg. malignancy, infection spreading in soft tissue
  • high risk of debilitating artefacts
  • patient factors - unable to sit still, unable to fit in machine (kyphotic pt or unfavourable neck to shoulder ratio)
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27
Q

Are UK undergraduates qualified to carry out CBCT?

A

Current UK teaching deemed inadequate to refer, justify, perform or interpret CBCT

28
Q

Name 5 other imaging modalities other than CBCT

A

1) CT conventional
2) MRI
3) Ultrasound
4) nuclear medicine
5) combination of multiple imaging modalities e.g. PET-CT, PET-MRI

29
Q

What is a CT (conventional) scan and what can be done to create contrast in the image produced?

A
  • cross-sectional imaging which allows soft tissue and bony anatomy to be visualised well.
  • may need iodinated contrast intra-venously to increase soft tissue contrast
30
Q

What are CT images constructed using?

A

voxels

31
Q

What kind of beam is used in CBCT?

A

Cone shaped beam

32
Q

What kind of beam is used in CT?

A

fan shaped beam

33
Q

What has a higher radiation dose, CT or CBCT?

A

CT

34
Q

What is the soft tissue contrast like in CBCT?

A

poor soft tissue contrast

35
Q

What is the soft tissue contrast like in CT?

A

good soft tissue contrast

36
Q

Is a IV radiographic contrast used in CBCT?

A

no

37
Q

How is a patient positioned for CBCT?

A

upright or sitting

38
Q

How is a patient positioned for CT?

A

lying horizontal

39
Q

CT voxels are given a value of density termed what?

A

Hounsfield units

40
Q

Newer CT units utilise what kind of voxels?

A

isotropic voxels - allow manipulation of images in all three planes (axial, coronal and sagittal) with no distortion

41
Q

What is air’s hounsfield number?

A

-1000, appears black

42
Q

What is fat’s hounsfield number?

A

-100 to -60

43
Q

What is the hounsfield number of water?

A

0

44
Q

What is the hounsfield number of dense bone?

A

+1000

45
Q

What is windowing?

A

alters levels of densities visualised in scan to optimally look at specific tissues
window level = value at centre of range
window width = range of values selected to view tissues

46
Q

What is the magnetic field for an MRI?

A

the entire room
imaging coil placed over region of interest to gain higher resolution

47
Q

In an MRI, what colour is cortical bone?

A

black

48
Q

In an MRI, what colour is fat and fluid?

A

white

49
Q

What are the advantages of an MRI?

A

no ionising radiation
very good imaging of soft tissues and early changes in bone marrow

50
Q

What are the disadvantages of an MRI?

A
  • multiple contraindications
  • lengthy scans
  • claustrophobia
  • cost and availability
51
Q

What are the contraindications for MRI?

A
  • pacemakers
  • orbital foreign bodies
  • artificial heart valves
  • surgical clips
52
Q

Why are implanted metals in the body a danger for MRI scanning?

A

metal attracted to magnetic field which means any metal in patient can be caused to move through the tissues causing pain or potentially fatality

53
Q

What are three examples of the uses of MRI in dentistry?

A

1) MRI TMJs - visualise cortical bone and articular disc in joint space (displacement, degenerative changes etc)
2) MRI salivary glands - detect masses
3) MRI sinus for malignancy - masses in sinuses

54
Q

How is an ultrasound scan carried out?

A
  • high frequency sound waves used to produce images
  • good for superficial structures
  • transducer placed on skin surface with coupling agent (gel) between probe and skin to allow soundwaves to penetrate
55
Q

How does an ultrasound scan produce an image and what can they not penetrate?

A

as sound waves hit tissue boundaries, they reflect back to probe
length of time to return creates level of depth
sound waves cannot penetrate bone

56
Q

What are the advantages of an ultrasound scan?

A
  • no ionising radiation
  • good for superficial structures
  • real time imaging
  • can be used as adjunct to biopsy/aspirates
  • blood flow
57
Q

What are the disadvantages of an ultrasound scan?

A
  • operator dependent
  • can’t penetrate bone
  • can be difficult to interpret
  • only superficial structures seen
58
Q

When can ultrasound scanning be utilised in head and neck?

A
  • neck lumps - cysts, tumours, lymph nodes
  • salivary glands - Sjogrens, neoplasia, sialadenitis, sialoliths
  • guidance for biopsy
  • vascular - carotid artery stenosis, vascular lesions
59
Q

What are three examples of nuclear medicine?

A

1) PET (positron emission tomography)
2) SPECT (single photon emission CT)
3) scintigraphy

60
Q

How does nuclear medicine generally work?

A

patient typically injected intra-venously with radiopharmaceutical which when it decays (via half life) emits particles that are picked up on gamma camera
- increased activity (hot spot)
- reduced/no activity (cold spot)

61
Q

What are the advantages of nuclear medicine scans?

A
  • can be superimposed over other cross sectional imaging (conventional CT)
  • highly sensitive
  • can assess function
62
Q

What are the disadvantages of nuclear medicine scans?

A
  • poor resolution
  • poor specificity
  • very high radiation dose
63
Q

What radioisotopes can be used in nuclear medicine?

A
  • Technetium - short half life (6hrs), can be bound to different substances that are taken up by specific tissues, MDP (bone) and pertechnetate (thyroid and salivary glands)
  • 18-FDG - fluoro-deoxyglucose (fluorine labelled glucose), short half life (just under 2hrs), gets taken up by metabolically active tissues
64
Q

What is a PET-CT scan?

A

positron emission tomography which is a type of nuclear medicine, superimposed over a conventional CT.
PET gives high sensitivity for increased glucose uptake
CT gives high resolution for anatomical detail

65
Q

What is a PET-CT scan typically used for?

A
  • cancer diagnosis
  • unknown primary disease ie. pt with solitary neck lump and nothing on clinical exam
  • can be used to assess recurrence, to assess effectiveness of treatment and to distinguish between active vs scar tissue

3rd year - module 6 (14 decks)

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