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SU14 Oral Radiology > EX2; Geometry of Image Formation > Flashcards

EX2; Geometry of Image Formation Flashcards

1
Q

This is how well defined is a boundary between two areas of differing radiodensities

A

image sharpness

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2
Q

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

A

image resolution

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3
Q

What are four desired characteristics of image formation

A

minimum magnification
distortion
superimposition
maximun detail

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4
Q

Does the x-ray beam diverge or converge

A

diverge

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5
Q

What three things does magnification depend upon

A

object-film distance
source-object distance
source-film distance

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6
Q

Does the magnification increase or decrease if there is a constant SOD and an increased OFD

A

increase

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7
Q

An increase in magnification affects the OFD how

A

increases

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8
Q

Does the magnification increase or decrease if there is a constant SFD and an increased OFD

A

increases

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9
Q

OFD should be small or large

A

small

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10
Q

Does the magnification increase or decrease if there in a constant OFD and a decreased SFD

A

increases

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11
Q

An increase in magnification affects SFD how

A

decreases

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12
Q

Does the magnification increase or decrease if there is a constant ODF and an increased SFD

A

decreased

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13
Q

SFD should be long or short

A

long

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14
Q

What are the dimensions of a short and long cone

A 
short = 8in or less
long = 12"-16"
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15
Q

This is variation seen in an image from the true shape or proportions of the object

A

distortion

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16
Q

What are the two types of distortion

A

size

shape

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17
Q

Distortion seen in an image is due to what

A

disproportionate (non-uniform_ magnification

some parts are more magnified than others

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18
Q

This occurs when object and sensor are parallel and the central ray is perpendicular to both the object and the film

A

minimun distortion

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19
Q

If the relationship between the object and film is angular (not parallel) what occurs

A

more acute distortion

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20
Q

If the central ray is directed at right angle to the object, what occurs

A

elongation

21
Q

If the central ray is directed at right angle to the sensor, what occurs

A

foreshortening

22
Q

If vertical angulation of the bisecting angle is too great, what occus

A

image foreshortening

image will shift occlusally or incisally

23
Q

If vertical angulation of the bisecting angle is too small, what occurs

A

image elongation

image will shift apically

24
Q

If vertical angle is too great of the parallel technique, what occurs

A

no foreshortening

the image will shift occlusally and may project off the receptor

25
Q

If vertical angle is too small of the parallel technique, what occurs

A

no additional elongation

image may shift apically; root apices may project off the receptor

26
Q

If a mistake is made using parallel technique, what occurs compared to bisecting angle

A

parallel technique mistake; magnification

BA technique mistake; elongation or foreshortening

27
Q

This is mandatory for paralleling technique due to a need for an increased SFD and not required for BA technique

A

long cone

28
Q

This refers to the recorded sharpness of boundaries of structures

A

radiographic definition (sharpness)

29
Q

What are four variables of radiographic definition

A

size of the source (focal spot)
OFD, SFD, SOD
movement
nature of image receptor

30
Q

The size of the source and definition are related how

A

inversely related

31
Q

These are factors that increase magnification and decrease definition

A

OFD
SFD
SOD

32
Q

This of the source of radiation; not vey significant; termed geometric unsharpness

A

movement

33
Q

This of the patients and/or image receptor; very significant; termed motion unsharpness

A

movement

34
Q

The source of radiation is superior to point of entry of CR (PRD pointing downwards) with what vertical angulation involving maxillary teeth

A

positive VA

35
Q

An increased or positive VA (maxillary) can cause the image to shift how

A

down; the occlusal/incisal edges may be projected off

36
Q

A decreased or negative VA (maxillary) can cause the image to shift how

A

up; the apices may project off the receptor

37
Q

The source of radiation is inferior to point of entry of CR (PRD pointing upwards) with what vertical angulation involving mandibular teeth

A

negative VA

38
Q

An increased VA (mandibular) can cause the image to shift how

A

up; the occlusal/incisal edges may be projected off

39
Q

A decreased VA (mandibular) can cause the image to shift how

A

down; the apices may project off the receptor

40
Q

The VA for all maxillary periodicals, bitewings, and occlusal radiographs is always what

A

positive; greater for PA than bitewings

41
Q

What is the angle of VA

A

0 degrees; CR parallel to occlusal plane

42
Q

What is the 0 degree of HA

A

CR is parallel to sagittal plane and directed anterioposteriorly

43
Q

What is the 90 degree of HA

A

CR is perpendicular to the sagittal plane

44
Q

What is the 180 degree of HA

A

CR is parallel to the sagittal plane and directed posteroanteriorly

45
Q

Improper HA can cause what

A

interproximal overlap

46
Q

Increasing HA causes images to what

A

shift anteriorly and results in overlapping

47
Q

Decreasing HA causes images to what

A

shift posteriorly and results in overlapping

48
Q

HA increases as the source of radiation moves where

A

posteriorly

49
Q

HA varies from what degrees in a PA

A

0 (incisor) to 90 (molar)

SU14 Oral Radiology (22 decks)

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