EX2; Geometry of Image Formation

Question 1

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

Answer 1

image sharpness

Question 2

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

Answer 2

image resolution

Question 3

What are four desired characteristics of image formation

Answer 3

minimum magnification
distortion
superimposition
maximun detail

Question 4

Does the x-ray beam diverge or converge

Answer 4

diverge

Question 5

What three things does magnification depend upon

Answer 5

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

Question 6

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

Answer 6

increase

Question 7

An increase in magnification affects the OFD how

Answer 7

increases

Question 8

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

Answer 8

increases

Question 9

OFD should be small or large

Answer 9

small

Question 10

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

Answer 10

increases

Question 11

An increase in magnification affects SFD how

Answer 11

decreases

Question 12

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

Answer 12

decreased

Question 13

SFD should be long or short

Answer 13

long

Question 14

What are the dimensions of a short and long cone

Answer 14

short = 8in or less
long = 12"-16"

Question 15

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

Answer 15

distortion

Question 16

What are the two types of distortion

Answer 16

size

shape

Question 17

Distortion seen in an image is due to what

Answer 17

disproportionate (non-uniform_ magnification

some parts are more magnified than others

Question 18

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

Answer 18

minimun distortion

Question 19

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

Answer 19

more acute distortion

Question 20

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

Answer 20

elongation

Question 21

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

Answer 21

foreshortening

Question 22

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

Answer 22

image foreshortening

image will shift occlusally or incisally

Question 23

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

Answer 23

image elongation

image will shift apically

Question 24

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

Answer 24

no foreshortening

the image will shift occlusally and may project off the receptor

Question 25

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

Answer 25

no additional elongation | image may shift apically; root apices may project off the receptor

Question 26

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

Answer 26

parallel technique mistake; magnification | BA technique mistake; elongation or foreshortening

Question 27

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

Answer 27

long cone

Question 28

This refers to the recorded sharpness of boundaries of structures

Answer 28

radiographic definition (sharpness)

Question 29

What are four variables of radiographic definition

Answer 29

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

Question 30

The size of the source and definition are related how

Answer 30

inversely related

Question 31

These are factors that increase magnification and decrease definition

Answer 31

OFD SFD SOD

Question 32

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

Answer 32

movement

Question 33

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

Answer 33

movement

Question 34

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

Answer 34

positive VA

Question 35

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

Answer 35

down; the occlusal/incisal edges may be projected off

Question 36

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

Answer 36

up; the apices may project off the receptor

Question 37

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

Answer 37

negative VA

Question 38

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

Answer 38

up; the occlusal/incisal edges may be projected off

Question 39

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

Answer 39

down; the apices may project off the receptor

Question 40

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

Answer 40

positive; greater for PA than bitewings

Question 41

What is the angle of VA

Answer 41

0 degrees; CR parallel to occlusal plane

Question 42

What is the 0 degree of HA

Answer 42

CR is parallel to sagittal plane and directed anterioposteriorly

Question 43

What is the 90 degree of HA

Answer 43

CR is perpendicular to the sagittal plane

Question 44

What is the 180 degree of HA

Answer 44

CR is parallel to the sagittal plane and directed posteroanteriorly

Question 45

Improper HA can cause what

Answer 45

interproximal overlap

Question 46

Increasing HA causes images to what

Answer 46

shift anteriorly and results in overlapping

Question 47

Decreasing HA causes images to what

Answer 47

shift posteriorly and results in overlapping

Question 48

HA increases as the source of radiation moves where

Answer 48

posteriorly

Question 49

HA varies from what degrees in a PA

Answer 49

0 (incisor) to 90 (molar)