Analogue Films

Question 1

What is the composition of a general analogue film?

Answer 1

Outside

Intra-oral film packet

• Plastic cover - moisture-proof
• Orientation dot (dot to the mesial)
• Inner paper wrap / black paper wrap - light-proof
• Lead foil backing - prevents residual radiation continuing on into patient’s tissues

Inside

Double emulsion film (2 emulsion layers)

• Emulsion = where image is recorded
  
  • Sensitive to x-rays, visible light & UV
  • Double layers (to reduce radiation dosage)
• Base = film support
  
  • Clear, transparent plastic
• Other:
  
  • Gelatin layer x2 (outer protective layer)
  • Adhesive layer x2 (between base & emulsion)

Question 2

What are the main components of the Emulsion layer?

Answer 2

• Silver halide crystals (or grains)
  
  • sensitive to x-ray photons!
  • Mostly silver bromide (Ag-Br) crystals
• Vehicle / Gelatin matrix
  
  • Suspends silver halide crystals
  • Allows efficient chemical processing
• Overcoat:
  
  • To protect crystals from damage eg. Scratch

Question 3

What is a latent image?

Answer 3

an image on an exposed film or print that has not yet been made visible by developing

CHEMICAL change in film emulsion after x-ray exposure:

• Silver bromide (Ag-Br) crystals in the emulsion layer have:
  
  • Free silver ions (positively charged) &
  • Sulfur compounds aka ‘sensitivity site’ (SS)
• Irradiated silver bromide release electrons and bind to ‘SS’
  
  • SS become negatively charged
• Free silver ions are attracted to –vely charged SS to form neutral silver atom

Question 4

How is a latent image processed to form a final image?

Answer 4

Processing tank (stainless steel)

CHEMICAL PROCESSING (4 steps)

1. Developing solution
2. Water
3. Fixing solution
4. Water & Dry & Mount

Other requirements

• Timer
• Dry zone / area
• Lightproof
• Humidity 50-70%
• Temperature 20-25°C (room temp)

Question 5

What chemicals are required for step 1: developing?

Answer 5

Target: latent image / exposed silver halide crystals

Chemicals used: (first 2 are active ingredients, they are developers – convert latent images to silver grains)

• Phenidone
  
  • converts latent image to metallic silver grains via oxidation
• Hydroquinone
  
  • reduces oxidated phenidone to help continuing its action
• Sodium sulphite
  
  • ​antioxidant preservative
• Potassium carbonate
  
  • activator
  • Maintains alkaline environment (developers need pH ~10)
  • Swells gelatin layer to let developing agents to diffuse more readily
• Benzotriazole
  
  • restrainer
  • Restrains developing unexposed Ag-Br crystals
  • Reduces image fogging
• Glutaraldehyde
• Fungicide
• Water

Duration: 3-6 minutes (depending on the temperature)

Question 6

Why is step 2: rinsing required?

(Rinse the film in water for with gentle agitation)

Answer 6

1. Prevent over-developing - Over-developed images = dark final image
2. Buffer to neutral pH

Duration: 20-30 seconds

Question 7

Which chemicals are required for step 3: fixing?

Answer 7

Target = unexposed silver halide crystals

Chemicals used:

• Ammonium thiosulphate
  
  • removes/dissolves unexposed silver halide crystals
• Sodium sulphate
  
  • preservative
• Aluminium chloride
  
  • hardener
  • Reduces swelling of the gelatin from subsequent handling
• Acetic acid
  
  • acidifier
  • Maintains acidic environment (pH 4-4.5) for the fixer
  • Inactivates residual developing solution, if any

Duration: 8-10 minutes

Question 8

Why is step 4: rinsing completed?

Rinse in water (in bath + under running water)

Answer 8

To:

1. Prevent over-fixing - Over-fixing causes light image
2. Remove all the silver thiosulfate complexes (they cause fixer stains = obvious radiopaque areas on the final image)

Question 9

What are the common processing errors?

Answer 9

• Light exposure in darkroom
  
  • Dark image = light leak into the darkroom
  • Film fogging (poor contrast, dark image) = prolonged exposure to safelight
• Poor handling
  
  • Fingerprints
  • Nails
  • Bent films
• Developing errors
  
  • Over-development = dark image
  • Under-development = light image
  • Contaminated film with developer before processing = black spots
• Fixing errors
  
  • Over-fixing = light image (or clear)
  • under-fixing = dark image
  • Contaminated film with fixer before processing = white / clear spots
  • Film in fixer before developer = clear image
• Rinsing errors
  
  • Inadequate washing of film to remove all fixer
  • Inadequate rinsing = Brown image (usually from fixer staining)
  • Over-rinsing = emulsion peel ie. No image

Question 10

Beam related error:
What causes underexposure? (light image)

Answer 10

1. Insufficient mA
2. Insufficient kVp
3. Insufficient time
4. Long film-source distance
5. Film reversed in mouth

Question 11

Beam related error:
What causes overexposure? (dark image)

Answer 11

1. Excessive mA
2. Excessive kVp
3. Excessive time

Question 12

What causes insufficient contrast?

Answer 12

1. Underdevelopment
2. Overexposure
3. Excessive kVP
4. Excessive film fog

Question 13

What causes film fog?

Answer 13

1. Improper safelighting
2. Light leaks
3. Overdevelopment
4. Contaminated solutions
5. Deteriorated films

Question 14

What causes dark spots?

Answer 14

1. Fingerprint contamination
2. Protective wrapping paper sticking to film surface
3. Film in contact with tank or another film during fixation
4. Film contaminated with developer before processing
5. Excessive bending of film
6. Static discharge to film before processing
7. Excessive roller pressure during automatic processing
8. Dirty rollers in automatic processing

Question 15

What causes light spots?

Answer 15

1. Film contaminated with fixer before processing
2. Film in contact with tank or another film during development
3. Excessive bending of film

Question 16

What causes yellow or brown stains?

Answer 16

1. Depleted developer or fixer
2. Insufficient washing
3. Contaminated solutions

Question 17

What causes blurring?

Answer 17

1. Movement of patient
2. Movement of x-ray tube head
3. Double exposure