Physics 2 Lecture

Question 1

Purpose of cassette

Answer 1

Prevent light from exposing film

Tight contract btw intensifying screen and film (light diffusion)

Prevent dirt/dust/hair artifacts

Lead layer on back side

Question 2

T/F Film is sensitive to xrays

Answer 2

F

IS NOT SENSITIVE

Question 3

What is exposing film, light or xrays?

Answer 3

light

Question 4

How are speed and resolution related

Answer 4

Inversely

Question 5

What is relationship of thickness of screen?

Answer 5

Thick-better absorption (decreased dose), less detail

Thin-less absorption (higher dose), higher resolution

Question 6

Intensifying screen speeds

Answer 6

Slow screens

• high resolution
• use with SA
• thin screen

Normal speed

Fast screens

• Low resolution
• use with LA
• thick screen

SPEED AND RESOLUTION ARE INVERSELY RELATED

Question 7

Film

• made of
• sulfur

Answer 7

Silver halide crystals
90-99% silver bromide
1-10% silver iodide

Sulfur= sensitivity speck (defect in crystals)

Question 8

How do you get a visible image on film

Answer 8

Light interacts with crystals to form a latent image

-THIS IS WHY WE DEVELOP FILM IN A DARK ROOM

Question 9

Explain how the reactions in film to get image

Answer 9

• light interacts w/bromide which releases e-
• e- is trapped by sensitivity speck (silver sulfide) and a negative charge is created at speck
• Negative charge attracts other silver ions
• Silver ion neutralized to form silver atom
• Silver atom acts as e- trap from other light interactions with bromide
• E- causes silver atom to be negatively charged
• Negatively charged silver attracts another silver ion
• These interact and form a 2 atom silver nucleus
• Continued electron trapping, neutralizing adding more silver ions
• Invisible latent image ready for processing.

Question 10

In film processing, areas of exposed crystals

-example

Answer 10

Are areas where x-ray photons were able to pass through patient and interact w/intensifying screen/film and will be BLACK

Crystals are converted to metallic silver= BLACK

Example= air/gas

Question 11

In film processing, areas of unexposed crystals

Answer 11

Are areas where xray photons were unable to pass through patient and interact w/intensifying screen/film

Crystals are washed away as they were not developed=WHITE

Example=metal/bone

Question 12

Film processing 3 steps

Answer 12

Developing
Fixing
Washing

Question 13

Developing

• exposed crystals
• unexposed crystals

Answer 13

Exposed

• Crystals have latent image center serve as catalyst
• Developer will reduce the remaining silver ions into metallic silver

Unexposed

• Can be developed but slow (no latent image center to provide catalyst)
• Majority will not become metallic silver
• Eventually are washed away

Question 14

Development depends on

Answer 14

time and temperature of solution

Question 15

Reasons for overdevelopment (image too dark)

Answer 15

• Unexposed crystals are converted to silver
• Too much time in developer
• Temperature too high

Question 16

Reasons for under-development (too white)

Answer 16

• Exposed crystals are not completely converted
• Not enough time in developer
• Temperature too low

Question 17

Film processing steps of FIXING

Answer 17

1-Stop action of developer
2-Remove unexposed crystals for emulsion
3-Hardens the emulsion

Question 18

Film processing step in WASHING

Answer 18

Removes excess chemicals

Question 19

Differences in automatic film processing vs manual

Answer 19

Automatic is much faster-higher temperature solutions and takes 90s vs 30-45 min

Disadvantages: messy, labor intensive

Question 20

In digital imaging types: what is the same and what is different

Answer 20

xray production is the same

detection is different

Question 21

3 types of digital imaging

Answer 21

Computed radiography (CR)
-indirect

Digital radiography (DR)

• direct
• indirect

Charged couple device (CCD)

**indirect=xray converted to light and then converted to electric signal

**direct=exray photon converted to electric signal