Projection Geometry-Day 2 Flashcards

1
Q

3 Problems in projection geometry

A

Unsharpness
magnification
distortion

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

3 Projection problems always present because

A

The focal spot is an area, never a point

The X-rays diverge from their source

Images are 2-D representations of 3-D structures

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

Spatial resolution

A

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

Measured in line pairs per mm

Higher spatial resolution is desirable

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

Sharpness

A

The degree of how well the image can display the boundary between two differing radiodensities

Sharp boundaries are desirable

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

Unsharpness at the boundary of an object is due to

A

penumbra and parallax

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

Penumbra

A

The space of partial illumination between the perfect shadow and full light

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

How to reduce penumbra

A

1) Use as small an effective focal spot as practical
- 0.4mm
2) Increase the distance between the focal spot and the object
3) Minimize the distance between the object and the image receptor

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

Parallax

A

Apparent change in position or size of a subject when viewed from different perspectives

Dental film – double emulsion

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

Movement due to

A

Just like a camera, create blurry lines:

Source movement (tube head movement)
Object movement (patient movement)
Receptor movement (patient movement of sensor/film in mouth)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Image size distortion due to

A

divergent paths of photons in x-ray beam

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

Image shape distortion due to

A

Unequal magnification in different parts of the same object

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

What is present in all radiographs

A

distortion

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

To decrease size distortion must

A

Increase in source to object

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