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Oral Radiology > Projection Geometry: Intraoral Radiographic technique (Exam 2) > Flashcards

Projection Geometry: Intraoral Radiographic technique (Exam 2) Flashcards

1
Q

Geometric characteristics include: (3)

A
  1. Image sharpness
  2. Image magnification
  3. Image shape distortion
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2
Q

Fuzzy, unsharp margin of radiographic image:

A

Unsharpness

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3
Q

Penumbra:

A

The unsharp margin of the image

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4
Q

Umbra:

A

Shadow

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5
Q

We want to minimize the _____ or maximize the ____

A

unsharpness; sharpness

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6
Q

What are the three rules to maximize sharpness?

A
  1. Radiation source should be as small as possible
  2. Source-to-object distance should be as long as possible
  3. Object-to-receptor distance should be as short as possible
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7
Q

What is the benefit of having a smaller focal spot?

A

Fewer X-ray photons that interact with the edge of the object leading to a sharper image

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8
Q

When we say the Source-to-object distance should be as long as possible, what is the source?

A

The focal spot

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9
Q

The closer the object is to the focal spot, the more _____ the X-ray photons are that are going to interact with the edges of the tooth

A

Divergent

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10
Q

The shorter the source-to-object distance, the greater the ______ meaning _____

A

Penumbra; the greater the unsharpness of the margin

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11
Q

How do we control the source-to-object distance?

A

By the length of the cone (longer cones better)

(its not exactly synonymous to source-to-object distance but we think of it as this way)

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12
Q

The X-rays beams will be more parallel to the object if we use a:

A

Longer cone

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13
Q

We have greater _____ with a longer object-to-receptor distance

A

Penumbra

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14
Q

You want the object or tooth to be as close to the ____ as possible

A

Image receptor

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15
Q

The equal enlargement of the object:

A

Magnification

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16
Q

Two rules to minimize magnification:

A
  1. source-to-object distance should be as long as possible
  2. object-to-receptor distance should be as short as possible
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17
Q

Enlargement of radiographic image, compared to actual size of object:

A

Magnification

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18
Q

If the distance from the source to the tooth is short then the X-rays that interact with the tooth are still going to be fairly _____ leading to ____

A

Divergent; greater magnification

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19
Q

If the distance form the source to the tooth is longer than the X-ray beam that interacts with the tooth is going to be fairly ____ leading to ____

A

Parallel; less magnification

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20
Q

Shape distortion has more to do with ____ than ____

A

Angles; distance

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21
Q

Unequal enlargement:

A

Distortion

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22
Q

not only is the object larger but the shape is inaccurate:

A

Distortion

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23
Q

Variation from true shape of object; unequal magnification of parts of object:

A

Distortion

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24
Q

Distortion can be caued by:

A

Improper alignment of receptor, object or beam

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25
Q

What are the rules for minimizing distortion?

A
  1. object and receptor should be parallel
  2. beam should be perpendicular to object & receptor
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26
Q

CR in the diagrams stands for:

A

Central ray

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27
Q

The radiographic image of the object is shorter than///

A

Foreshortening

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28
Q

Tooth is not parallel to receptor and beam directed perpendicular can lead to what type of distortion?

A

Forshortening & elongation

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29
Q

The radiographic image is longer than the object itself:

A

Elongation

30
Q

Tooth not parallel to receptor, and beam directed perpendicular to tooth:

A

Elongation

31
Q

Five rules for accurate image formation:

A
  1. focal spot as small as possible
  2. source-object distance as long as possible
  3. object-receptor distance as short as possible
  4. object parallel to receptor
  5. beam perpendicular to object and receptor
32
Q

Projection techniques for periapical radiography: (2)

A
  1. paralleling technique - use long cone
  2. bisecting angle technique - use long or short cone
33
Q

What are the two steps to the paralleling technique?

A
  1. receptor parallel to tooth
  2. beam perpendicular to tooth/receptor
34
Q

In the paralleling technique when having the receptor parallel to the tooth, we want _____ object-receptor distance, and ____ source-receptor distance

A

increased; increased

35
Q

What balances out the increased object-receptor distance when using the paralleling technique?

A

increased source-to-receptor distance (minimizing unsharpness & magnification)

36
Q

What type of cone is used to increase the source-to-receptor distance using the paralleling technique?

A

Long cone

37
Q

Getting the image receptor parallel to the teeth allows for correct _____ angulation

A

vertical

38
Q

If you’re using the XCP correctly and you line up the beam with the cone, the X-ray beam will image:

A

the entire area of interest (no cone cuts)

39
Q

Getting a cone cut autonatically means you have to retake image (T/F):

A

False (as long as you obtain the area of interest you don’t have to retake)

40
Q

Cone cuts show up on radiographs as:

A

White areas

41
Q

If the contacts are open in the area of interest this tells us the _____ angulation is correct

A

horizontal

42
Q

The _____ is the preferred technique but the ___ technique may be used if the first choice technique does not work

A

Paralleling technique; bisecting angle technique

43
Q

With the bisecting angle technique, you are not trying to get the image receptor parallel to the tooth, but rather just trying to get it _____ to the tooth

A

Close

44
Q

The bisecting angle technique is based on:

A

The rule of isometry

45
Q

In the bisecting angle technique, if two triangles have two equal angles and a common side, then:

A

The two triangles are equal

46
Q

According to the bisecting angle technique if you direct the X-ray being perpendicular to the bisecting line that you estimated when lining things up you should:

A

Get a pretty good image

47
Q

The bisecting angle technique states that the angle formed by the plane of the tooth and plane of receptor is bisected and the beam is directed ____ to the bisecting line

A

Perpendicular

48
Q

Why is the paralleling technique preferred over the bisecting angle technique?

A

a little more distortion with the bisecting angle technique

49
Q

preferred image for checking bone level:

A

Bitewing

50
Q

The ___ technique has more limitations than the ____ technique

A

Bisecting angle technique; paralleling technique

51
Q

The bitewing is used to see:

A

Crowns, interproximal bone levels, alveolar bone support, caries, periodontal condition, calculus and crown margins

52
Q

Bitewings are not used to view:

A

Periapical regions of the tooth

53
Q

Bitewing technique : The ____ angle is more of a challenge than the ___ angle

A

Horizontal; vertical

54
Q

In the bitewing technique, you’d like us to have a _____ vertical angulation

A

slightly positive (+5 to 10 degrees depending on location)

55
Q

If the horizontal angulation is incorrect in bitewing radiographs, then the image will display:

A

Overlapping contacts

56
Q

____ includes periapical and bitewing radiographs showing all teeth

A

Full mouth series

57
Q

When viewing radiographs, whats on the providers right is actually the patients:

A

Left

58
Q

Radiographic localization includes: (2)

A
  1. right angle method
  2. tube shift method (SLOB)
59
Q

States if you take radiographs at right angles to eachother of the areas of interest you can localize the area in question:

A

Right angle method

60
Q

The right angle method states:

A

if you take radiographs at right angles to eachother of the areas of interest you can localize the area in question:

61
Q

SLOB stands for:

A

Same Lingual Opposite Buccal

62
Q

In the tube shift method, you will take a second radiograph of the same area but alter the:

A

Horizontal angulation

63
Q

In the tube shift method, if you take the first radiograph straight on, you may take the second radiograph _____ (for example)

A

mesially or distally (or even vertically)

64
Q

If the object moves in the same diredction as you move the tube head, than the object is ____ to the reference point (same)

A

Lingual

65
Q

When using the slob rule, if the object moves in the opposite direction as the tube head was moved, than the object is ____ to the reference point (opposite)

A

Buccal

66
Q

First radiograph: supernumerary tooth overlapping mesial of the root

Using SLOB method you move tube mesially in second radiograph

Second radiograph: the supernumerary tooth now does not overlap the mesial root of the second molar (shifter slightly mesial)

This means the lesion is:

A

Lingual

67
Q

The tube shift method for radiographic localization may also be referred to as:

A

SLOB

68
Q

Edge gradient; the unsharp area; area around the margins of the object:

A

Penumbra

69
Q

What do we try to minimize when taking radiographs?

A

Penumbra

70
Q

How do we minimize penumbra?

A

By having an increased source to object ratio

71
Q

Three factors that affect the quality of a ra

A

Oral Radiology (21 decks)

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