Unit 2 Radiographic Quality Factors II: Contrast

Question 1

Image Contrast

Answer 1

The differences between adjacent areas of IR exposure on the image

1. Differences in IR exposure
2. Capabilities of processing and monitor

Question 2

Dynamic Range

Answer 2

Range of brightness of the display monitor

Question 3

Window Width

Answer 3

Post-processing function that allows the user to produce changes in displayed shades of gray

Question 4

Window level vs. Window width

Answer 4

-Window Level: changes the level of brightness (center shade of gray) displayed on the viewing monitor
-Window Width: changes the displayed CONTRAST (the number of shades of gray displayed) on the viewing monitor

Question 5

Physical Contrast vs Visible Contrast

Answer 5

-Physical Contrast: Recorded on the Image Receptor
-Visible Contrast: Displayed on the Viewing Monitor

Question 6

Long Scale Contrast

Answer 6

• Differences between adjacent shades of gray is small
• Many Shades of Gray
• More diagnostic information

Question 7

Short Scale Contrast

Answer 7

• Differences between adjacent shades of gray is large
• Fewer Shades of Gray
• Less diagnostic information

Question 8

High contrast vs Low contrast

Answer 8

-High Contrast: extremely bright and dark areas
-Low contrast: many shades of gray, very little difference between light and dark areas

Question 9

What type of contrast is most desirable?

Answer 9

Long scale contrast because there is more diagnostic information

Question 10

What is Total image contrast? What 2 sub-types of contrast make it up?

Answer 10

-A result of the total amount of contrast from both the anatomical part and image processing.
-Subject contrast and Image contrast

Question 11

Subject Contrast

Answer 11

Differences in intensity of the beam after it has been attenuated by the tissue, Differential Absorption

Question 12

What is the controlling factor for subject contrast?

Answer 12

kVp (absorption of the x-ray beam)

Question 13

Subject contrast: High kVp vs Low kVp

Answer 13

-High kVp = more uniform penetration of the body = Long Scale Contrast
-Low kVp = more photons absorbed = Short Scale Contrast

Question 14

Subject Contrast and Differential Attenuation:

Answer 14

-High subject contrast occurs when the differences in absorption properties of adjacent tissues of body parts is High
-Low subject contrast occurs when the differences in absorption properties of adjacent tissues of body parts is Low

Question 15

How does tissue atomic number affect subject contrast?

Answer 15

-High Atomic Number Increases absorption (Photoelectric Interactions)
-High subject contrast occurs when the differences in adjacent atomic numbers of tissues in High

Question 16

Atomic numbers for Soft tissue, Barium sulfate, and Iodine

Answer 16

Soft tissue: 7.3
Barium Sulfate: 56
lodine: 53

Question 17

Subject Contrast and Tissue Density

Answer 17

-High tissue density Increases absorption
-Increased differences in absorption between adjacent tissue means Increased subject contrast

Question 18

T or F: As contrast decreases, scatter radiation increases

Answer 18

True

Question 19

kVp is the Controlling Factor for Subject Contrast, but it also controls
_________ __________ in the tissue and the relationships between _________ and __________

Answer 19

-Differential Absorption
-Photoelectric and Compton

Question 20

As kVp increases, PE(photoelectric) ____________, Compton ____________, and Contrast ___________

Answer 20

Decreases; Increases; Decreases

Question 21

Look Up Table (LUT)

Answer 21

Stored data used to map incoming exposure data with a gray shade on the monitor

Question 22

Image contrast vs Subject contrast

Answer 22

Image contrast: BY the computer
Subject contrast: TO the computer

Question 23

Subject Contrast influencing factors

Answer 23

OID
Grid use
Beam restriction
Contrast media
Patient factors
Scatter

-OID Reduces scatter = Increases subiect contrast
-Beam Restriction Reduces scatter = Increases subject contrast
-Patient Factors Part thickness, atomic #, tissue density all affect Photoelectric (increased PE = increased contrast)
-Grid Use Reduces scatter = Increases subject contrast