10.07 Extraoral plain skull Flashcards Preview

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Flashcards in 10.07 Extraoral plain skull Deck (27)
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1
Q

for an extraoral film cassette what is the front surface made of?

A

the front surface is the tube side, and should be made of thin material with a low atomic number (plastic, Bakelite) to allow as much radiation through as possible

2
Q

what is attached to each cover of an extraoral film cassette, and why?

A

an intensifying screen with a compression device such as foam between the screen and cover to maintain close contact between the screen and film

3
Q

for an extraoral film cassette, what is the back cover made of, and why?

A

should be made of heavy metal (lead-lined aluminum) to minimize backscatter

4
Q

intensifying screens are coated with…

A

plastic intensifying screens are coated with a layer of flat crystals of lanthanum or gadolinium (rare earth screen)

5
Q

what is the purpose of the crystal in the intensifying screens?

A

when ionizing radiation strikes these phosphors, they absorb the energy which has penetrated through the patient and emit it as a flash of visible light in the green portion of the visible light spectrum
-thus the inten. screen allow for a significant reduction in exposure to radiation bc it is a combo of radiation and visible light which exposes the film

6
Q

why would you take an extraoral plain skull projection?

A

-when pathology is encountered and you need to get better 3D visualization

7
Q

which extraoral plain skull projection would be best to visualize the medial and lateral wall of the maxillary sinuses? (including the medial wall of the orbit free of superimposition of the petrous ridges of the temporal bone)

A

-Water’s view (occipitomental)

8
Q

what does Water’s View (occipitomental) permit assessment of?

A

the zygomatic buttresses, orbital rims, nasal bones, anterior lamina papyracea and ethmoid air cells and frontal sinusus
-only view which projects the anterior and posterior ethmoid air cells separately

9
Q

which is the only view which projects the anterior and posterior ethmoid air cells separately

A

-Water’s view (occipitomental)

10
Q

Positioning for Water’s View (extraoral plain skull projection)

A
  • sagittal plan perpendicular to film
  • chin raised high so canthomeatal line is 37 degrees above horizontal
  • central ray should be perpendicular to the film through the midsagittal plane at the level of the maxillary sinus
  • source-film distance 36-40’’
11
Q

which projection best demonstrates the midline and posterior facial structures?

A

Posteroanterior projection

12
Q

projection of choice for demonstration of orbits, frontal and ethmoid sinusues and nasal fossa,

  • lamina papyracea well visualized
  • good for detecting mediolateral changes in the skull including asymmetry
A

posteroanterior projection

13
Q

if you wanted to visualize the lower half of the maxillary sinuses, what projection would NOT be used and why?

A

posteroanterior projection, due to superimposition of the petrous ridges

14
Q

positioning for posteroanterior view/projection

A
  • head is centered in front of cassette with canthomeatal line parallel to the floor, placing the occlusal plane in a horizontal position
  • central ray is directed perpendicular to the plane of the film, with a source-film distance of 36-40’’
  • source should be coincident with the midsagittal plane of the head at the level of the bridge of the nose
15
Q

which projection would be used to evaluate the anterior and posterior walls of the maxillary, frontal, ethmoid and sphenoid sinuses and the pterygomaxillary buttress?

A

lateral projection

16
Q

what is the best projection for evaluating an air-fluid level in the maxillary sinuses?

A

lateral projection

17
Q

which view demonstrates the relationship of the sphenoid sinus to the sella turcica and the nasopharyngeal soft tissues and airway?

A

lateral projection

18
Q

positioning for lateral projection

A
  • left side of face adjacent to cassette and midsagittal plane parallel with the film
  • central ray is oriented toward the external auditory meatus and perpendicular to the midsagittal plane and the plane of the film
  • source-film distance is 36-40’’ (standard)
19
Q

what is different for cephalometric projections than lateral projections?

A

the source-film distance is 60’’ insctead of 36-40’’ and a wedge filter is placed over the anterior side of the beam at the tube head to reduce the intensity of radiation in the region and help reveal soft tissue profile

20
Q

which projection demonstrates the base of the skull, the position and orientation of the condyles, the curvature of the mandible, the lateral wall of the maxillary sinuses, and the pterygoid plates?

A

the Submentovertex projection (SMV)

21
Q

which view best demonstrates fractures of the zygomatic arch?

A

Submentovertex projection (SMV)

22
Q

which is the only projection that demonstrates the left and right sphenoid sinuses separately

A

the submentovertex projection (SMV)

23
Q

positioning for the submentovertex view

A
  • patients head is extended backward with the vertex on the center of the cassette
  • the midsagittal plane must remain perpendicular to the floor
  • the canthomeatal line should extend 10 degrees past vertical
  • the central ray is projected from below the mandible up toward the vertex of the skull, to pass about 2 cm. in front a line connecting the left and right condyles
  • fro viewing the sygomatic arches specifically, the exposure time is ruduced to 1/3 that used to visualize the skull.
24
Q

-for viewing the zygomatic arches specifically, what is done compared to a normal SMV projection?

A

the exposure time is reduced to 1/3 that used to visualize the skull.

25
Q

which projection is the most important plain film for assessing subcondylar fractures as it is the only one which optimally demonstrates the angulation and/or displacement that occurs

A

Reverse-Towne’s projection

26
Q

Reverse-Towne’s projection

A
  • the most important plain film for assessing subcondylar fractures as it is the only one which optimally demonstrates the angulation and/or displacement that occurs
  • alos permits evaluation of the petrous ridges and mastoid air cells and the posterolateral wall of the maxillary antrum
27
Q

positioning for the Reverse-Towne’s view

A
  • head in front of the cassette with the canthomeatal line oriented downward 25-30 degrees. The condylesare better visualized if the patient’s mouth is fully opened
  • the central ray is directed toward the film in the sagittal plane through the occipital bone the beam is collimated to the areas of interest to reduce patient exposure and film fog