Film Imaging

Question 1

What is image receptor made from?

Answer 1

Film and screen

Question 2

What is the film made from?

Answer 2

A protective transparent coat
Emulsion
Adhesive layer
Base

Question 3

What is the film emulsion made from?

Answer 3

Silve halide

90% silver bromide, 10% silver iodide

Question 4

What is the adhesive layer and base used for?

Answer 4

Adhesive layer sticks the emulsion to the base

The base is used for structure

Question 5

What is the screen made from?

Answer 5

Protective layer - transparent
Phosphor
Reflective layer
Base plate

Question 6

What is phosphor used for in screen?

Answer 6

To convert x-ray into light

Question 7

What is use of reflective layer?

Answer 7

Reflect light back towards film?

Question 8

What interactions are present in image receptor?

Answer 8

X-ray interact w/ phosphor layer - converts energy into photos
Photons emitted all directs = activation Silver halide = area blackening

Question 9

What does x-ray speed depend on?

Answer 9

Thickness of phosphor layer - the thicker that phosphor more chance of x-ray interaction

Crystal size - larger = more blackening = worse resolution = increased speed

Question 10

How is resolution affected by speed?

Answer 10

Increased speed = reduced resolution

Question 11

What is purpose of light absorbing dyes?

Answer 11

Prevent the light from spreading too far - increases resolution but decrease speed

Question 12

What is latent image formation?

Answer 12

X-ray hits crystal giving e- in bromide enough energy to escape = sensitivity speck

E- is negative and attract mobile Ag+ = Ag atom = silver deposits which are more sensitive to developed = blackening

Question 13

What is developer?

Answer 13

Alkali which acts as a reducing agent
Converts Ag+ –> Ag by addition of electron
Process begins at sensitivity speck

Question 14

What happens if image developed for too long?

Answer 14

AgBr crystal converted to silver = black film

Question 15

What does washing do?

Answer 15

Stops developer

Question 16

What if fixing?

Answer 16

An acid which removes unreacted silver halide

Question 17

What is purpose of final wash?

Answer 17

Fixed solution still slightly sensitive to light - must be remove or will react producing brown stain

Question 18

What has happened if image too dark?

Answer 18

Overexposed or developed/ fogging due to storage

Question 19

What is image too pale - what happened?

Answer 19

Underexposed or underdeveloped

Question 20

What has happened if opaque film?

Answer 20

Inadequate fixing or final wash

Question 21

What happens with age of film or inappropriate storage?

Answer 21

Background fog

Fog blackening can happen from background radiation

Question 22

What happens at higher x-ray beam (dose)

Answer 22

Lower pt dose

D films are slow
E/F films are faster

Question 23

What is the ideal film geometry?

Answer 23

Parallel to avoid stretch or magnification

Detector close to tooth to reduce spread

Question 24

Why can’t focal spot be too small?

Answer 24

Generate too much heat

But if too large = spread = blur

Question 25

What is crystal size related to?

Answer 25

Resolution

Question 26

What is resolution determined by in digital radiology?

Answer 26

Pixel size

Density of CR/DR system

Question 27

How does computed radiographs differ?

Answer 27

Have image plate and reader w/ PSP instead of film