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SU14 - Radiology Exam 2 > geometry of image formation > Flashcards

geometry of image formation Flashcards

1
Q

image sharpness

A

how well defined is a boundary between 2 areas of differing radiodensities (i.e. DEJ)

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2
Q

image resolution

A

how well an image is able to reveal very small objects that are very close together

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3
Q

what are the 4 desired characteristics of image formation?

A

minimum magnification
minimum distortion
minimum superimposition
MAXIMUM detail

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4
Q

magnification depends on what 3 distances?

A
  1. object-film distance (OFD)
  2. source-object distance (SOD)
  3. source-film distance (SFD)
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5
Q

We want OFD to be ________ for clear and sharp images.

A

SHORT

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6
Q

we want SFD to be ________ for defined images

A

LONG

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7
Q

if you increase OFD, the magnification _______

A

increases

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8
Q

constant OFD + decreased SFD ____________ magnification

A

increases

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9
Q

constant OFD + increased SFD ___________ magnification

A

decreases

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10
Q

constant SOD + increased OFD (film moves away from object) __________ magnification

A

increases

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11
Q

constant SFD + increased OFD (object moves toward source) ____________ magnification

A

increases

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12
Q

decreased SFD __________ magnification

A

increases

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13
Q

4 names for source of radiation

A

source
target
focal spot
anode

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14
Q

distortion

A

variation seen in image from true shape or proportions of object

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15
Q

distortion in an image is due to what?

A

disproportionate magnification

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16
Q

distortion depends on ___________; magnification depends on __________

A

angulation; distance

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17
Q

minimum distortion occurs when object and sensor are ________ and central ray is ______________ to both __________ and _______

A

parallel
perpendicular
object
film

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18
Q

what happens when central ray is directed at right angle to object?

A

elongation

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19
Q

what happens when central ray is directed at right angle to sensor?

A

foreshortening

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20
Q

parallel technique

- image shifts __________ if vertical angle is too great and shifts _____________ if vertical angle is too small

A

occlusally

apically

21
Q

bisecting angle technique
– image shifts __________/_________ if vertical angle is too great and shifts _____________ if vertical angle is too small

A

occlusally/incisally

apically

22
Q

paralleling technique (3 characteristics)

A
  • placement of sensor parallel to teeth is easy
  • if mistake is made no foreshortening or magnification
  • long cone is mandatory due to need for increased SFD
23
Q

bisecting angle technique (3 characteristics)

A
  • direct invisible central ray of invisible x-ray beam at right angle to imaginary bisector
  • if mistake is made it will result in foreshortening or elongation
  • long cone is not necessary
24
Q

radiographic definition

A

recorded sharpness of boundaries of structures

25
Q

umbra

A

innermost and darkest part of a shadow where light source is completely blocked by occluding body

26
Q

the _________ the umbra, the sharper the image

A

smaller

27
Q

penumbra

A

space in periphery of main target of radiation therapy

28
Q

size of source is _________ related to definition

size of source is _________ related to unsharpness

A

inversely

directly

29
Q

all factors that ________ magnification will decrease definition

A

increase

30
Q

movement of source of radiation =

A

geometric unsharpness

31
Q

movement of patient or image receptor =

A

unsharpness

32
Q

zero degree VA

A

central ray is parallel to occlusal plane

33
Q

increased/positive VA: source of radiation is __________ to point of entry of central ray (PID is pointing _________) and the image shifts _________ (_______/_________ edges may be projected off receptor)

A

superior
downwards
down
incisal/occlusal

34
Q

are all maxillary radiographs positive?

A

yes

35
Q

decreased/negative VA: image shifts ____ (_______ may be projected off receptor)

A

up

apices

36
Q

for mandibular teeth a the source of radiation for negative VA is _________ to point of entry of central ray. PID is pointing _________

A

inferior

upwards

37
Q

are all mandibular radiographs negative?

A

yes

38
Q

increasing VA in mandibular teeth causes image to shift ______ where what edges may be projected off the receptor?

A

up

occlusal/incisal

39
Q

decreasing VA in mandibular teeth causes image to shift _____ where ______ may be projected off the receptor

A

down

apices

40
Q

VA for maxillary periapicals is ____________ than bitewings

A

greater

41
Q

VA for maxillary anterior periapicals is __________ than VA for posterior periapicals

A

greater

42
Q

Horizontal angulation

- 0 degrees: central ray is _________ to sagittal plane and directed _____________

A

parallel

anteroposteriorly

43
Q

HA

- 90 degrees: central ray is __________ to sagittal plane

A

perpendicular

44
Q

HA

- 180 degrees: central ray is __________ to sagittal plane and directed _____________

A

parallel

posteroanteriorly

45
Q

improper HA causes _________

A

interproximal overlapping

46
Q

increasing HA causes images to shift ____________

decreasing HA causes images to shift ___________

A

anteriorly

posteriorly

47
Q

source of radiation moves ____________

A

posteriorly

48
Q

in periapical radiography, HA varies from ____ degrees (incisor PA) to _____ degrees (molar PA)

A

0-90

SU14 - Radiology Exam 2 (5 decks)

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