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SAQs for dentistry > Radiology > Flashcards

Radiology Flashcards

1
Q

What is the absorbed dose?

A

The mean energy imparted to a unit mass of tissue by ionising radiation. It is measured in grass

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2
Q

What is the equivalent dose?

A

Takes into account the fact that different types of ionising radiation are more damaging to certain types of tissues, so different weightings are given to the absorbed dose. Within dental radiography the absorbed dose and the equivalent dose is the same. It is measured in joules per kg but is termed sieverts

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3
Q

What is the effective dose?

A

Takes into account the fact that some tissues are more susceptible to the effects of ionising radiation than others.

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4
Q

What factors can influence the effective dose which the patient receives?

A
  • the sensitivity of the image receptor
  • the area exposed to the primary beam
  • exposure factors such as low dose
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5
Q

When writing a radiographic report regarding periodontal bone loss it used to be common practice to express this in millimetres from the cementoenamel junction to the crest of the alveolar bone. Why is this not considered to be accurate?

A

Any direct measurement taken from a radiograph may be inaccurate as the image it depicts may be distorted by being shortened or lengthened. Also it does not take into account the length of the root of the tooth

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6
Q

What formula is used to represent a more acceptable way to describe the severity of bone loss nowadays?

A

CEJ to bone crest (in mm)/ CEJ to root apex (in mm) x100

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7
Q

What are the main patterns of bone loss?

A

Horizontal bone loss occurs when the base of the pocket lies coronal to the bony crest, creating a supra bony pocket
Vertical bone loss is where more bone loss occurs on one side of the interdental bone crest than on the other. This leaves the base of the pocket within the bony defect and is an infra bony pocket

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8
Q

What do you understand by the term cone beam computed tomography?

A

It is a three dimensional digital radiographic image. A Ct image is generated by a CT scanner using X-rays to produce a sectional or slice image of the body. The data are in a numerical format and converted into a grey scale representing different tissue densities which generates an image. In conventional or medical CT the X-ray beam is fan shaped but in CBCT the beam is cone shaped

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9
Q

List two advantages and two disadvantages of CBCT

A

Advantages:

  • multiplayer imaging and manipulation so the anatomy can be seen in different planes
  • low radiation dose relative to conventional medical CT
  • fast scanning time
  • compatible with implant and cephalometric planning software
  • cheaper and smaller than conventional medical CT

Disadvantages:

  • all information/data are obtained in a single scan so patient must remain stationary
  • soft tissue is not imaged in detail
  • artefacts from metal objects e.g restorations
  • reconstructed dental panoramic image is not directly comparable with the conventional dental panoramic radiograph
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10
Q

What is a tomography?

A

It is a technique for producing images of a slice or section of an object

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11
Q

How is tomography achieved?

A

The X-ray tube and the film cassette carrier are connected and move synchronously but in opposite directions about a pivoting point. The pivoting point will appear in focus on the radiograph

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12
Q

What is a focal trough?

A

Only a slice of the object in in focus on the tomography and this is called the focal trough

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13
Q

What do you understand by the term ghost shadows with respect to dental panoramic radiography?

A

Ghost shadows are shadows cast by anatomical structures such as the cervical vertebrae and the mandible and the palate, which are outside the focal trough on the panoramic radiograph. They appear on the opposite side of the real image counterpart and slightly higher up than the real image

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14
Q

What would an air shadow look like on a dental panoramic tomography and why do they take on this appearance?

A

Air shadows are radiolucent because there is no photon absorption whereas there is in tissue

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15
Q

What error would have produced the film showing anterior teeth that are out of focus and magnified?

A

The patient is positioned too far from the film

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16
Q

What error would have produced the molars being larger on one side than the other?

A

The patient has their head to one side or the other so they are asymmetrically positioned in the machine

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17
Q

What error would have produced vertical or horizontal distortion of one part of the image?

A

The patient has moved whilst the radiograph has been taken

18
Q

What error would have produced the radiograph being too dark?

A

Overexposure- due to increased exposure time either by operator error or faulty equipment
Overdevelopment- due to excessive time in the developer solution, the solution being too warm or too concentrated
Fogging- due to poor storage of the film or light leaking onto film during development
Patient with very thin tissues

19
Q

What do you understand by the terms development and fixation when it comes to radiographs?

A

Development is when the sensitised silver halide crystals in the film emulsion are converted to metallic silver, which is black in colour and produces the black/grey part of the image
Fixation is when the unsensitised silver halide crystals on the film emulsion are removed. This produces the white/transparent part of the image

20
Q

List five methods you could use to minimise the radiation dose to a patient having an intraoral radiograph

A
  • justification
  • high speed film
  • rectangular collimation
  • quality control
  • optimal kilovoltage
  • digital radiography
  • aluminium filtration
  • use of film holders
  • appropriate focus to skin distance
  • the fastest speed film should be used that will give a good quality image
  • when referring a patient the radiographs should be sent with them to avoid having further radiation
21
Q

How does ionising radiation damage the body?

A

The effects can cause direct or indirect damage. Direct damage involves ionising biological molecules, e.g. point mutations in DNA. Indirect damage occurs from ionising water, which leads to the formation of free radicals. These may combine to form highly reactive species which cause damage

22
Q

What radiograph would you need for internal derangement of the temporomandibular joint?

A

MR scan

23
Q

What radiograph would you need for a fluid level in the maxillary antrum?

A

10* occipitomental radiograph

24
Q

What radiograph would you need for a blow out fracture of the orbital floor?

A

CT scan of the face

25
Q

What radiograph would you need for a salivary calculus in the submandibular duct?

A

Mandibular standard occlusal radiograph

26
Q

What radiograph would you need for the presence of an impacted permanent upper canine?

A

Maxillary standard occlusal radiograph

27
Q

What is sialography? Give 2 indications and contraindications for using it

A

Sialography involves introducing a radiopaque medium into the ductal system of a major salivary gland and then taking a radiographic image

Indications:

  • obstructions in the ductal system e.g calculi
  • it is used to assess the structure of the gland and ductal system to see if there is any destruction or changes in them

Contraindications:

  • allergy to iodine containing compounds
  • infection in the gland
  • a calculus close to the duct orifice which may be pushed further back by the introduction of contrast medium
28
Q

On which radiographic views would you see submandibular duct salivary calculi?

A

Dental panoramic radiograph and lower standard occlusal

29
Q

Give 4 advantages of using ultrasound to image salivary glands

A
  • no ionising radiation used
  • excellent for superficial masses
  • can use it to guide fine needle aspiration
  • can use it to differentiate between solid and cystic masses
  • it can identify radiolucent calculi not seen on radiographs
30
Q

Describe what a keratocystic odontogenic tumour may look like on a radiograph

A
  • radiolucent lesion
  • well defined
  • multilocular although may be unilocular
  • rounded margins
  • adjacent teeth may be displaced
  • tooth roots are not usually absorbed
31
Q

Describe what a dentigerous cyst may look like on a radiograph

A
  • radiolucent lesion
  • well circumscribed
  • usually unilocular but there may be pseudo-loculation due to bony trabecular
  • rounded
  • contains the crown of a tooth, or lies adjacent to the crown of the tooth
  • associated tooth is usually displaced
32
Q

If a patient had a lesion at the angle of the mandible what radiographic views could be taken to demonstrate it and what would each view show?

A

A dental panoramic radiograph, sectional dental panoramic tomography or oblique lateral views would show the lesion. The mesiodistal and superior/inferior dimensions of the lesion would be evident as well as association with any teeth, the inferior dental canal etc. A posterior anterior view of the mandible will show any buccolingual expansion of the mandible

33
Q

Give an advantage of using the bisected angle technique instead of the paralleling technique?

A
  • positioning of the film packet in any area of the mouth is usually more comfortable for the patient
  • it is straightforward and quick
  • the length of the crowns and roots should be the same as the teeth being radiographed if the film and tube have been correctly positioned
34
Q

What are the advantages of using a paralleling technique?

A
  • there is no image distortion
  • images are reproducible at different visits with different operators
  • there is no coning off of the image
  • rectangular collimation will reduce the radiation dose to patients
  • periodontal ben levels and the crowns of teeth are well shown
  • there is no superimposition of the zygomatic buttress on the maxillary molars
35
Q

What is the controlled area?

A

The controlled area is within the primary beam until it has gone far enough to be reduced in strength or gone through shielding. It also includes the area around the patient and X-ray tube

36
Q

What measures are advised with regards to the control area?

A

Hazard lights should be illuminated during the exposure and signs on the door are needed

37
Q

Digital radiography is becoming more popular. What is used instead of a film packet when taking a digital radiograph?

A

A charged couple device (CCD), a complementary metal oxide semi conductor, a photostimulable phosphor imaging plate

38
Q

Give four advantages of digital radiography over conventional radiography

A
  • no processing faults
  • no risk from handling the chemicals involved in processing
  • lower radiation dose as the image receptors are more sensitive than conventional film
  • ease of storage of images
  • ease of transfer of images
  • electronic enhancement of images
39
Q

Give four indications for an occipitomental view

A
  • suspected fracture of the zygomatic complex
  • middle third facial injuries
  • le fort I, II, III fractures
  • nasoethmoidal complex fractures
  • orbital fractures
  • coronoid process fractures
  • frontal sinus and ethmoidal sinus visualisation
40
Q

What are the differential diagnosis for a radiolucency at the angle of the mandible?

A
  • ameloblastoma
  • odontogenic keratocyst
  • calcifying epithelial odontogenic tumour
  • myxoma
  • ameloblastic fibroma
  • haemangioma

SAQs for dentistry (4 decks)

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