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Flashcards in Projection Geometry Deck (27):
1

What are three problems that will always be present in radiographs

unsharpness, magnification, distortion

2

Why are there always projection problems

1. the focal spot is an area, never a point
2. The X-rays diverge from their source
3. Images are 2-d representation of 3 d structures

3

What is sharpness

the degree of how well the image can display the boundary between two differing radio densities

4

the unsharpness at the boundary of an object

penumbra

5

Spatial resolution

the degree of how well the image can display two objects that are close together

6

How is spatial resolution measured

line pairs/ mm
lp/mm

7

_______ spatial resolution is desirable

higher

8

Spatial resolution and sharpness are both influenced by

1. focal spot size
2. receptor composition
3. movement

9

____ focal spot size has higher sharpness and spatial composition

small

10

Order the following receptors based on there sharpness and spatial resolution
PSP, Film, CCD, CMOS

Film> CCD> CMOS > PSP

11

Movement of the tube head is

source movement

12

movement of the patient is

object movement

13

patient movement of sensor/film in mouth is

receptor movement

14

Large focal spot will cause sharpness to

decrease

15

long source to object distance will cause sharpness to

improve

16

long object to receptor distance will cause sharpness to

decrease

17

What angulation is the dental x-ray set at

20 degrees

18

What is the size of the focal spot in dental X-rays

1mmx3mm

19

Distortion can cause

foreshortening or elongation

20

foreshortening is due to

the tooth not parallel to the receptor, beam perpendicular to the receptor

21

elongation is due to

the receptor is not parallel to the tooth and it is not perpendicular to the beam, but is perpendicular to the beam

22

this technique increased sharpness, and decrease distortions

parallel technique

23

In parallel technique the tooth is parallel to the

receptor

24

This technique is used due to its accuracy in length

bisecting angle

25

A downfall of the bisecting technique is

the distortion of other anatomic features

26

two ways to improve image distortion

1. object parallel to the receptor
2. beam is perpendicular to the long axis of the tooth

27

What are methods to localize objects in radiographs

SLOB and cone beam computed tomography, image at right angle to the