L3 Analogue Films and Film Faults

Analogue Films and Common Film Faults¹

Dr Dayea Oh

OMF Radiologist

Introduction to Intraoral Radiography²³

Review of Intra-oral Radiography

Intra-oral Radiography:

• 2D, diagnostic imaging using ionising radiation (= x-ray beam)
• Clinical workflow:
  • Film / receptor placed intra-orally → Expose (the film & the patient) with x-ray beam → film processing → diagnostic image production
• Images are of black (radiolucent), white (radiopaque) and grey ‘shadows’
• Three types:
  • Bitewing (BW), Periapical (PA) & Occlusal
  • Digital or analogue

Left Posterior Bitewing (BW)

Learning Objectives⁴

• Understand the composition of a general analogue film
• What is a latent image?
• How is a latent image processed to form a final image?
• What are the factors that affect the final image quality?
• Understand how to assess faulty radiographs

Analogue Film Composition

External Packet Components⁵

What you’ll see on the 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
• ANALOGUE FILM

Internal Film Structure⁶

What you can’t see inside…

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

Fig. 4.3 Diagram showing the cross-sectional structure of double emulsion radiographic film.

Emulsion Components⁷

Emulsion

• Main components:
  • 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 from damage eg. Scratch

Latent Image Formation⁸

• = exposed film → CHEMICAL change in film emulsion after x-ray exposure

Silver bromide (Ag-Br) crystals in the emulsion layer have:

• Free silver ions (positively charged) and;
• 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 negatively charged SS to form neutral silver atom

Remember – only IRRADIATED (EXPOSED) Ag-Br crystals form latent image

Photon (wave shown) Ag (atom symbol) Br (atom symbol) e- (electron symbol) SS (sensitivity site shown as cloud) Br—Ag—Br Br—Ag+—Br Br Br—Ag—Br Ag—Ag Ag Ag—Br—Ag—Br—Ag—Br—Ag

Chemical Processing Steps⁹

Latent Image to Final (Visible) Image

• 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 → ‘safelight’ Red GXB-2 filter (7.5-15W bulb)
  • Humidity → 50-70% relative humidity
  • Temperature → 20-25°C (room temp)

Developing Process¹⁰

Chemical Processing – 1. Developing

• Target: latent image / exposed silver halide crystals
• Chemicals used:
  • 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)

Rinsing Process¹¹

Chemical Processing – 2. Rinsing

• Rinse the film in water with gentle agitation
• To:
  • Prevent over-developing
    • Over-developed images = dark final image (film fog)
  • Buffer to neutral pH
• Duration: 20-30 seconds

Fixing Process¹²

Chemical Processing – 3. Fixing

• 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

Final Rinsing and Drying¹³¹⁴

Chemical Processing – 4. Final Rinsing

• Rinse in water (in bath + under running water)
• To:
  • Prevent over-fixing
    • Over-fixing causes light image
  • Remove all the silver thiosulfate complexes (they cause fixer stains = obvious radiopaque areas on the final image)

graph TD
    A[Unexposed film & Ag-Br] --> B[Only exposed Ag-Br form latent image]
    B --> C["Latent image become real image (image at this stage has fogging due to presence of remaining unexposed Ag-Br)"]
    C --> D[After fixing \(final image\)]

Darkroom Protocols and Automation

Daily Start-up Protocol¹⁵

Darkroom Daily Start-up Protocol

• Clean & dry benches
• Check safelight & check for any light leaks
• Check chemical solutions (developers & fixers)
  • Check the volume & temperature
  • Stir to equalise the temperature throughout the tanks
• Step-wedge test (mainly to test developer)
  • Compare daily ‘test film’ with initial ‘reference film’
    • Reference film = processed film when developer & fixer were newly replenished / replaced
  • When an optical difference is noted, all chemicals need replacement
• Weekly clearing time test (fixer efficacy)
  • Measure time taken to remove all silver halide crystals (unexposed film)
    • Ideal = 8-10 min (at room temperature ~ 25°C)
    • Replace fixer if the clearing time doubles

Automatic Processing Systems¹⁶¹⁷

Automatic Processing

• Manual processing can take up to >10 min.
• Compact ‘darkroom’ unit
  • No need for a separate dedicated darkroom
• Fast process
  • Passes successively through the developer -> fixer -> water -> and drier (usually 5 min)
  • High concentration of hydroquinone in developing solution
  • Often, inadequately rinsed -> discolouration

graph TD
    A[Film entry] --> B[Developing solution]
    B --> C[Fixing solution]
    C --> D[Water wash]
    D --> E[Drying elements]
    E --> F[Film exit]

Film Viewing and Storage¹⁸¹⁹

Analogue Film Viewing

• Mount ONLY DRY films
• Check orientation
• Mandatory information on mounted films:
  • Patient detail (name, gender, DOB)
  • Date of exposure
  • Type of film
  • Institution / address of practice
  • Exposure details (if possible)
• Light box

Film Storage

• Medicolegally, all films must be kept for 7 years*

  • If child, for 7 years after turning 18 years old

• Stored in a cool, dry place

• Check AHPRA / ARPANSA / Radiation Health (in QLD) annually for any change

Radiographic Film Faults²⁰

Common Film Faults

Processing and Handling Errors²¹

• Processing Errors - I
• 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

The provided text is an order of operations for handling images and text:

Image Rules²²

• Image Only: If the figure is an image with only labels or sparse text, output ONLY a brief 2-5 word description wrapped in “ tags.
• Image Context: If the text on the page only makes sense in the context of a figure or image (labels, names with no context), treat the whole page as a figure: wrap a single brief description in “ tags and output NOTHING ELSE.
• Constraints: NEVER output image descriptions as plain text outside of tags, and NEVER output standard HTML image tags (<img src="...">), nor wrapper tags like <div> or <figure>.

Text Rules

• Extract all text and prioritize image text, using PDF text to resolve ambiguities.
• Format bold text using bolding.
• Ignore obviously corrupted text.
• Format tables in HTML (only tables, nothing else).
• Format flowcharts as tables.

The input consists of six dental radiographs without any accompanying labels. Therefore, applying the Counting the Text and Image Rules, the appropriate response is a brief description of the entire figure containing the dental X-rays.

Fixing Errors²³

• 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 rinsing → Brown image (usually from fixer staining)
• Over-rinsing → emulsion peel, i.e., no image

Beam Related Errors²⁴²⁵

• Exposure setting errors
  • Underexposure → light image
    • Insufficient mA
    • Insufficient kVp
    • Insufficient time
    • Long film-source distance
    • Film reversed in mouth
  • Overexposure → dark image
    • Excessive mA
    • Excessive kVp
    • Excessive time
• Beam misalignment → Cone-cutting (partial image)

Causes of Faded or Washed Out Images

Positive-Fading or Washed Out (Fig. 5-34)²⁶

Causes in Exposure Factors

• Incorrectly installed long-focus cone tip
• Film-source distance is too far
• Excessive kVp
• Power-failure during exposure
• Not using film cassette or trouble with cassette (bending)

Causes in Processing

• Improper time-temperature setting for development (too cool)
• High concentration of developer solution
• Stale developer solution
• New and fresh fixer solution
• Failure to fix (insufficient time in fixer)
• Developer has not reached the film during processing
• In prolonged processing, the film was agitated too little

Negative-Fading or Densification (Fig. 5-35)

• Insufficient time

• Insufficient current (mA)?

• Insufficient kVp

• Power-failure during exposure

• Not using film cassette or trouble with cassette (bending)

• Inadequate or old developer solution

• Excessive development time for solution temperature

• Old fixer solution

• In new film processing, insufficient agitation time of the developer

White Blends (Fig. 5-36)

Cause in Exposure Factors

• Improperly exposed or old double emulsion X-ray films
• Film brought into contact with fluorescent lamps

Cause in Processing

• Improper time-temperature setting for development (too cool)
• Undiluted or insufficiently diluted developer solution
• Stale developer solution
• Improper film sorting class
• Improper storage of films in humid or hot conditions

Radiation (Fig. 5-37)

• Wrong focal length for the case

• X-ray tube malfunction

• Long exposure time (usually not more than 12 seconds)

• Not enough kVp

• Failure of the X-ray machine

• Improper time-temperature setting for development (too cool)

• Long development time

• Too much agitation

• Inadequate or old developer solution

• Improper film sorting class

• Operator’s overexposure of the film (excessive-dose)

• Operator’s underexposure of the film (insufficient-dose)

• Failure of the X-ray machine

Dusty Spots (Fig. 5-38)

• External objects in the field of the beam
• Operator’s overexposure of the film (excessive-dose)

Radioactivity (Fig. 5-39)

• Kernel of radioactive element in the film

Chair, Acetone, and Oil (Fig. 5-40)

• Overly dense areas in the film
• Operator’s overexposure of the film (excessive-dose)

Handlers Hallmarks (Fig. 5-41)

• Operator’s overexposure of the film (excessive-dose)

Bibliography²⁷

Fifth Edition Essentials of Dental Radiography and Radiology Eric Whaites, Nicholas Drage CHURCHILL LIVINGSTONE ELSEVIER

ORAL RADIOLOGY Principles and Interpretation Edition 7 Stuart C. White, Michael J. Pharoah ELSEVIER

Footnotes

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