Lec 5 Projection Geometry

Question 1

Reliability of the image to represent the true state of the anatomic region examined.

Answer 1

Image quality

Question 2

Basic Principles of Projection Geometry:
1. The focal spot should be ______ as possible.
2. The source-receptor distance should be as _____ as possible.
3. The object-receptor distance should be as ____ as possible.
4. The receptor should be _____ to the long axis of the object.
5. The central beam should be _______ to the object and the receptor.

Answer 2

• small
• long
• small
• parallel
• perpendicular

Question 3

Measures how well a boundary between two areas of differing radiodensity is revealed.

Answer 3

Sharpness

Question 4

Measures how well a radiograph reveals small objects that are close together.

Answer 4

Spatial resolution

Question 5

The resulting blurred zone at the edge of the image causes a loss in image sharpness.

Answer 5

Geometric unsharpness / penumbra

Question 5

Also known as PENUMBRA

Answer 5

Geometric unsharpness

Question 6

Ideal focal spot measurement.

Answer 6

0.4 to 0.7mm

Question 7

• _______ focal spot adds sharpness
• _______ focal spot prolongs tube life but results in loss of image quality
• _______ focal spot has a greater wearing effect on the target but results in an increased image sharpness

Answer 7

• smaller
• bigger
• smaller

Question 8

Increase the distance between the source and the object by using a _________________?

Answer 8

Long, open-ended cylinder

Question 9

Increasing the source-to-object distance reduces _____________?

Answer 9

Geometric unsharpness

Question 10

Ideal distance between the source and the object?

Answer 10

8 inches to 16 inches

Question 11

___________ the distance between the object and the image receptor.

Answer 11

Minimize

Question 12

Use as _________ an effective focal spot as _______.

Answer 12

Small; practical

Question 13

The increase in size of the image on the radiograph compared with the actual size of the object.

Answer 13

Image size distortion

Question 14

Dependent on source-to-object and object-to-image receptor

Answer 14

Image size distortion

Question 15

Unequal magnification of different parts of the same object.

Answer 15

Image shape distortion

Question 16

To minimize shape distortion, the practitioner should align the x-ray tube, object, and image receptor according to the following guidelines:
1. Position the image receptor _______ to the long axis of the object.
2. Orient the central ray ______ to the object and image receptor

Answer 16

parallel; perpendicular

Question 17

Radiographic image to be shorter than the object.

Answer 17

Foreshortening

Question 18

Radiographic image to be longer than the object.

Answer 18

Elongation

Question 19

Place image receptor _______ to the long axis of the tooth, and directs the central x-ray beam ________ to both the long axis of the tooth and the receptor.

Answer 19

parallel; perpendicular

Question 20

Place image receptor _______ to the long axis of the tooth, and directs the central x-ray beam ________ to both the long axis of the tooth and the receptor.

What technique?

Answer 20

• parallel; perpendicular
• paralleling technique

Question 21

Place ___________ parallel to the long axis of the ______, and directs the _______ perpendicular to both the _____ and the _______.

What technique?

Answer 21

• image receptor; teeth
• central x-ray beam; long axis of the tooth & receptor
• paralleling technique

Question 22

Preferred method?

Answer 22

Paralleling technique

Question 23

Central ray _________ to an imaginary plane that bisects the angle between the ____ and the __________.

What technique?

Answer 23

• perpendicular
• teeth & image receptor
• bisecting-angle technique