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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
angle bisector principle: CR should be directed at a ___ angle to the line _____ the angle between the vertical axis of the ____ (object) and the ____
right, bisecting, tooth, film
26
vertical axis of object and film are parallel and CR is directed at right angle
parallel principle/technique
27
two principles in intraoral radiography
parallel principle | angle bisector principle
28
proper results in paralleling technique
magnification present | minimum distortion
29
proper results in bisecting angle technique
length of image/object equal | distortion present
30
issues with parallel principle
no elongation/foreshortening, but magnification
31
is a long cone necessary for angle-bisector or for parallel principle?
parallel principle (d/t increased OFD)
32
recorded sharpness of boundaries of strucutres
radiographic defintion
33
definition and sharpness are synonymous, t/f?
true
34
variables of defintion
- size of source - OFD, SFD, SOD - movement - nature of film - intensifying screen
35
size of source and definition is ___ related
inversely
36
size of source and unsharpness are ____ related
directly
37
darkest part of the shadow
umbra
38
almost shadow, around the periphery of dark shadow, a light shadow is present
penumbra
39
the farther the film, the ___ the penumbra
greater
40
increase SFD to decrease _____
penumbra
41
___ ___ technique can create a sharper image
long cone
42
all factors that increase ______ will decrease definition
magnification
43
two types of movement that produce unsharpness
movement of source, movement of patient
44
positive vertical angle
cone pointing downward
45
0 degree vertical angle
cone parallel to occlusal plane
46
negative vertical angle
cone pointing upward
47
+VA used for...
- Mx periapicals - Mx occlusals - bitewing
48
-VA used for...
- Mn periapicals | - Mn occlusals
49
too high of a +VA will cause images to shift ____
down (opposite to source)
50
too high of a +VA will lose ___________ off film
incisal/occlusal edges
51
too low of a VA+ will cause images to shift ___
up (opposite to source)
52
too low of a +VA will lose ___________ off film
root apices
53
increasing -VA will cause images to shift ____
up
54
increasing -VA will lose ______ off film
incisal/occlusal edges
55
decreasing -VA will cause images to shift ___
down (opposite of source)
56
decreasing -VA will lose ____ off film
root apices
57
usually, VA for Mx periapical is _____ than for bitewing
greater (bitewing has less +VA)
58
+VA for Mx anteriors is ____ than Mx posteriors
greater
59
with parallel principle, change in VA causes _____ or ____ image shift
occlusal/incisal, apical
60
with angle-bisector principle, change in VA cause _____ as well as ____/_____.
image shift, elongation/foreshortening
61
Mn molar area can have VA of ____ or ___
+5, 0 (can be slightly positive, not always -VA)
62
horizontal angle 0 degrees CR ____ to ____ _____ running _____-_____
parallel, sagittal plane, antero-posteriorly
63
horizontal angulation of 180 degrees direction
CR running postero-anteriorly
64
improper HA leads to...
interproximal overlapping
65
increasing HA causes image shift _____
anteriorly
66
decreasing HA causes image shift ____
posteriorly

x.umn radiology (15 decks)

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