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x.umn radiology > Geometry of Image Formation > Flashcards

Geometry of Image Formation Flashcards

1
Q

desired characteristics of radiographs. Minimum or maximum…

  • magnification?
  • distortion
  • superimposition
  • detail
A
  • min. magnification
  • min. distortion
  • min. superimposition
  • maximum detail
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2
Q

magnification controlled by these 3 differences

A
  • OFD (object-film distance)
  • SOD (source-object distance)
  • SFD (source-film distance)
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3
Q

a short PID is __ inches or less

A

8 inches

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4
Q

a long PID is around ___ inches, but varies __-___ inches

A

16, 12-18 inches

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5
Q

magnification should be _______, keeping minimum magnification

A

true to size

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6
Q

unequal magnification is…

A

distortion

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7
Q

superimposition is…

A

overlap (ex: canine over premolar)

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8
Q

SOD is the distance from ___ to ____

A

source to tooth (object)

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9
Q

SFD is the distance from ___ to ____

A

source to film

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10
Q

OFD is the distance from ___ to ____

A

tooth (object) to film

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11
Q

magnification always occurs due to

A

diverging nature of x-ray beam

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12
Q

other words for sources of x-ray beam

A

source, target, focal spot, anode

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13
Q

**do the hand/flashlight demonstration for the exam. did you do it?

A

I hope you did!

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14
Q

with a constant SOD, increased OFD will ____ magnification

A

increase

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15
Q

with constant SFD, increased OFD will ___ magnification

A

increase

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16
Q

OFD should be as ___ as possible, which impacts ___ ____

A

small, image sharpness

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17
Q

with a constant OFD, decreasing SFD will decrease magnification, true or false?

A

false, it will increase

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18
Q

minimum magnification:

film ________ tooth as possible; source _______

A

as close to, farther away

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19
Q

variation of image from true shape or proportionality of object

A

distortion

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20
Q

two types of distortion

A

size distortion

shape distortion

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21
Q

minimum distortion occurs when object and film are ____ and the central ray is at a ____ angle to both the object/film

A

parallel, right

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22
Q

distortion that occurs if CR is directed at right angle to object

A

elongation distortion

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23
Q

distortion that occurs if CR is directed at a right angle to film

A

foreshortening distortion

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24
Q

rule of isometry/angle bisector principle in radiology

A

keep angles bisected equally to prevent distortion

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25
Q

angle bisector principle: CR should be directed at a ___ angle to the line _____ the angle between the vertical axis of the ____ (object) and the ____

A

right, bisecting, tooth, film

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26
Q

vertical axis of object and film are parallel and CR is directed at right angle

A

parallel principle/technique

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27
Q

two principles in intraoral radiography

A

parallel principle

angle bisector principle

28
Q

proper results in paralleling technique

A

magnification present

minimum distortion

29
Q

proper results in bisecting angle technique

A

length of image/object equal

distortion present

30
Q

issues with parallel principle

A

no elongation/foreshortening, but magnification

31
Q

is a long cone necessary for angle-bisector or for parallel principle?

A

parallel principle (d/t increased OFD)

32
Q

recorded sharpness of boundaries of strucutres

A

radiographic defintion

33
Q

definition and sharpness are synonymous, t/f?

A

true

34
Q

variables of defintion

A
  • size of source
  • OFD, SFD, SOD
  • movement
  • nature of film
  • intensifying screen
35
Q

size of source and definition is ___ related

A

inversely

36
Q

size of source and unsharpness are ____ related

A

directly

37
Q

darkest part of the shadow

A

umbra

38
Q

almost shadow, around the periphery of dark shadow, a light shadow is present

A

penumbra

39
Q

the farther the film, the ___ the penumbra

A

greater

40
Q

increase SFD to decrease _____

A

penumbra

41
Q

___ ___ technique can create a sharper image

A

long cone

42
Q

all factors that increase ______ will decrease definition

A

magnification

43
Q

two types of movement that produce unsharpness

A

movement of source, movement of patient

44
Q

positive vertical angle

A

cone pointing downward

45
Q

0 degree vertical angle

A

cone parallel to occlusal plane

46
Q

negative vertical angle

A

cone pointing upward

47
Q

+VA used for…

A
  • Mx periapicals
  • Mx occlusals
  • bitewing
48
Q

-VA used for…

A
  • Mn periapicals

- Mn occlusals

49
Q

too high of a +VA will cause images to shift ____

A

down (opposite to source)

50
Q

too high of a +VA will lose ___________ off film

A

incisal/occlusal edges

51
Q

too low of a VA+ will cause images to shift ___

A

up (opposite to source)

52
Q

too low of a +VA will lose ___________ off film

A

root apices

53
Q

increasing -VA will cause images to shift ____

A

up

54
Q

increasing -VA will lose ______ off film

A

incisal/occlusal edges

55
Q

decreasing -VA will cause images to shift ___

A

down (opposite of source)

56
Q

decreasing -VA will lose ____ off film

A

root apices

57
Q

usually, VA for Mx periapical is _____ than for bitewing

A

greater (bitewing has less +VA)

58
Q

+VA for Mx anteriors is ____ than Mx posteriors

A

greater

59
Q

with parallel principle, change in VA causes _____ or ____ image shift

A

occlusal/incisal, apical

60
Q

with angle-bisector principle, change in VA cause _____ as well as ____/_____.

A

image shift, elongation/foreshortening

61
Q

Mn molar area can have VA of ____ or ___

A

+5, 0 (can be slightly positive, not always -VA)

62
Q

horizontal angle 0 degrees CR ____ to ____ _____ running _____-_____

A

parallel, sagittal plane, antero-posteriorly

63
Q

horizontal angulation of 180 degrees direction

A

CR running postero-anteriorly

64
Q

improper HA leads to…

A

interproximal overlapping

65
Q

increasing HA causes image shift _____

A

anteriorly

66
Q

decreasing HA causes image shift ____

A

posteriorly

x.umn radiology (15 decks)

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