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radiology > Radiology 14 - Dental Panoramic Radiography > Flashcards

Radiology 14 - Dental Panoramic Radiography Flashcards

1
Q

What does attenuation between the x-ray tube and receptor do?

A

Alters the number of photons that reach the receptor.

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2
Q

What forms the latent image?

A

The direct actions of photons on emulsion/ phosphor plate.

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3
Q

What is a tomograph?

A

A radiograph showing a slice or section of a tissue in focus –> tissue in focus called the focal trough or plane.

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4
Q

what do multiple tomographs of sequential planes give rise to?

A

a 3D image, ex. a CT.

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5
Q

What is a DPT

A

A type of tomography that brings the teeth and supporting structures into focus.

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6
Q

What is narrow beam rotational tomography?

A

synchronized movement of tubehead and film/sensor in HORIZONTAL plane (cassete at front of face tubehead and back of head).

carrier cassette and tubehead move in OPPOSITE direction, film and tube head move in SAME direction.

CIRCULAR path, SINGLE CENTRE of rotation, focal trough is a single arch of a circle.

LIMITED USE IN DENTISTRY AS DENTAL ARCH NOT PART OF A CIRCLE.

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7
Q

How is a DPT taken

A

Similar principle to narrow beam rotational tomography but with USUALLY TWO CENTERS OF ROTATION

(tube behind patient moving from right to left, sensor/ cassette in front moving from left to right of patient synchronized with tubehead)

Beam angled upwards about 8 degrees to horizontal.

Can be taken with either conventional film or digital (phosphor plates or solid state sensor/ CCD).

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8
Q

What other imaging types can a DPT machine be used for?

A

A lateral ceph. (With an additional lateral ceph. attachment). or a CBCT

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9
Q

What is the shape of the focal trough produced by a DPT

A

Horse shoe- shape (narrow anteriorly, wide posteriorly) –> corresponds to elliptical shape of dental arch.

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10
Q

what is a disadvantage of DPTs?

A

Non conventional arch shape may not conform to focal trough and image quality may suffer.

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11
Q

What is a disadvantage of using indirect film ad intensifying screens for DPT? What is an advantage?

A

Disadvantage: Light from intensifying screen is emitted in all directions hence light affects larger area of film than a single photon –> IMAGE QUALITY NOT AS GOOD AS DIRECT FILM.

Advantage: Dose is reduced.

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12
Q

What is the use of a bite block for a DPT?

A

To bring the mandible into the same/ middle of the focal trough as the maxilla into an EDGE TO EDGE INCISAL RELATIONSHIP.

impossible to do if you have a class III incisal relationship.

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13
Q

5 advantages of DPT?

A
  • shows teeth and facial bones
  • shows both sides –> allows for comparison
  • shows vertical height of mandible and ID canal
  • shows maxillary sinus walls
  • lower dose and less time than intraoral radiographs.
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14
Q

disadvantages of DPT

A
  • superimposition of soft and hard tissues
  • lack of fine detail
  • patient must be correctly position and co operation requires
  • image magnified due to OBJECT-RECEPTOR DISTANCE.
  • Exposure time up to 16 seconds.
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14
Q

5 disadvantages of DPT

A
  • superimposition of soft and hard tissues
  • lack of fine detail
  • patient must be correctly position and co operation requires
  • image magnified due to OBJECT-RECEPTOR DISTANCE.
  • Exposure time up to 16 seconds.
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15
Q

7 indications for DPT

A
  • Lesion not completely visible on intra-oral
  • Gross dental disease/neglect
  • Symptomatic third molars
  • Orthodontic assessment
  • Mandibular fractures
  • Degenerate disease of TMJ
  • Implant planning or review
16
Q

What are 7 patient position requirements for DPT?

A
  • remove metal jewellery, appliances, dentures and glasses
  • straight spine and hold handles
  • bite biteblock with incisors edge to edge
  • light beam markers (to make sure mid sagittal is vertical and frankfort is horizontal)
  • head immobilized
  • tongue on roof of mouth
  • stand still
17
Q

Do we use lead apron for DPT

A

NO JUSTIFICATION for use of lead aprons in dental radiography, does NOT protect from internal scatter, interferes with DPT.

18
Q

What are ghost images?

A

Images of a structure on one side which are projected onto the other side (ramus and angle of mandible, hard palate, foreign bodies ex. earrings, surgical clips).

ghost images always seen at HIGHER LEVEL than real structure bc x-ray beam is 8 degrees point upwards.

19
Q

what will be the appearance of DPT if there is an AP error - too far back?

A

Too far from the receptor –> widened, magnified, out of focus teeth.

20
Q

what will be the appearance of DPT if there is an AP error - too far forwards?

A

Too close to the receptor –> narrowed incisors.

21
Q

what will be the appearance of DPT if the chin is tipped down?

A

The Frankfort plane will not be horizontal, can cause:
- out of focus lower incisors/ anterior teeth
- distorted occlusal plane (SMILEY FACE)
- excessive ghost shadows (ex. of spine or mandible).

22
Q

what will be the appearance of DPT if patient does not keep tongue on ROM?

A

There will be a radiolucent band across the film.

23
Q

what will be the appearance of DPT if there is a horizontal rotation of the patient?

A

The DPT will be asymmetrical,

ex. if patient rotate to the RIGHT, RIGHT molars are closer to receptor and SMALLER, LEFT molars father from receptor and LARGER/ magnified.

24
Q

what will be the appearance of DPT if the chin is tipped up?

A

The Frankfort plane will not be horizontal, can cause:
- out of focus upper incisors
- distorted occlusal plane (GRUMPY FACE) OR FLAT OCCLUSAL PLANE
- excessive ghost shadows (ex. of spine or mandible).

(SEE PAGE 126 OF BOOK)

25
Q

Are DPTs good for caries diagnosis?

A

Not gold standard due to overlap (esp. in premolar region), superimposition of anatomy/air and poor fine detail.

HOWEVER useful when there is strong gag reflex and suggested DPT may be better for occlusal caries diagnosis, especially in molars.

26
Q

Where do caries most often occur in children?

A

Usually caries are approximal.
Hence because panoramic has overlap of contact points, bitewings are preferred.

radiology (8 decks)

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