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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

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

A

image resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are four desired characteristics of image formation

A

minimum magnification
distortion
superimposition
maximun detail

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Does the x-ray beam diverge or converge

A

diverge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What three things does magnification depend upon

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

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

A

increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

An increase in magnification affects the OFD how

A

increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

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

A

increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

OFD should be small or large

A

small

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A

increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

An increase in magnification affects SFD how

A

decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

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

A

decreased

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

SFD should be long or short

A

long

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the dimensions of a short and long cone

A
short = 8in or less
long = 12"-16"
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

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

A

distortion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the two types of distortion

A

size

shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Distortion seen in an image is due to what

A

disproportionate (non-uniform_ magnification

some parts are more magnified than others

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

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

A

more acute distortion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
If vertical angle is too small of the parallel technique, what occurs
no additional elongation | image may shift apically; root apices may project off the receptor
26
If a mistake is made using parallel technique, what occurs compared to bisecting angle
parallel technique mistake; magnification | BA technique mistake; elongation or foreshortening
27
This is mandatory for paralleling technique due to a need for an increased SFD and not required for BA technique
long cone
28
This refers to the recorded sharpness of boundaries of structures
radiographic definition (sharpness)
29
What are four variables of radiographic definition
size of the source (focal spot) OFD, SFD, SOD movement nature of image receptor
30
The size of the source and definition are related how
inversely related
31
These are factors that increase magnification and decrease definition
OFD SFD SOD
32
This of the source of radiation; not vey significant; termed geometric unsharpness
movement
33
This of the patients and/or image receptor; very significant; termed motion unsharpness
movement
34
The source of radiation is superior to point of entry of CR (PRD pointing downwards) with what vertical angulation involving maxillary teeth
positive VA
35
An increased or positive VA (maxillary) can cause the image to shift how
down; the occlusal/incisal edges may be projected off
36
A decreased or negative VA (maxillary) can cause the image to shift how
up; the apices may project off the receptor
37
The source of radiation is inferior to point of entry of CR (PRD pointing upwards) with what vertical angulation involving mandibular teeth
negative VA
38
An increased VA (mandibular) can cause the image to shift how
up; the occlusal/incisal edges may be projected off
39
A decreased VA (mandibular) can cause the image to shift how
down; the apices may project off the receptor
40
The VA for all maxillary periodicals, bitewings, and occlusal radiographs is always what
positive; greater for PA than bitewings
41
What is the angle of VA
0 degrees; CR parallel to occlusal plane
42
What is the 0 degree of HA
CR is parallel to sagittal plane and directed anterioposteriorly
43
What is the 90 degree of HA
CR is perpendicular to the sagittal plane
44
What is the 180 degree of HA
CR is parallel to the sagittal plane and directed posteroanteriorly
45
Improper HA can cause what
interproximal overlap
46
Increasing HA causes images to what
shift anteriorly and results in overlapping
47
Decreasing HA causes images to what
shift posteriorly and results in overlapping
48
HA increases as the source of radiation moves where
posteriorly
49
HA varies from what degrees in a PA
0 (incisor) to 90 (molar)