Comprehensive notes on QA/QC in Radiography

Diagnostics, Quality Assurance, and Quality Control in Radiography

  • Grid and procedure chain
    • Grids improve image quality by stopping scatter radiation from reaching the image receptor (x-ray machine → grid → film).
    • Components in the imaging chain include automatic and manual film processors, film feed, wash, developer, fixer, water, and rollers (PVC/ rubber).
    • Equipment used in viewing and processing: Negatoscope/viewbox, film, film processor (automatic & manual), and film scanner.

Radiographic Image Quality: Definitions and Core Concepts

  • Fidelity of radiographic imaging
    • Refers to how faithfully the anatomical structures are represented on the radiograph.
    • A radiograph that faithfully reproduces structure and tissues is a High-Quality Radiograph.
  • The most important characteristics of radiographic quality
    • Spatial Resolution
    • Contrast Resolution
    • Noise
    • Artifacts
  • Interrelated qualities
    • Radiographic Quality is often discussed in terms of Resolution, Speed, and Noise, which are interrelated.
  • Spatial vs. Contrast resolution
    • Spatial Resolution: ability to image small objects and distinguish details (detail)
    • Contrast Resolution: ability to distinguish anatomical structures with similar subject contrast (recorded detail)

Radiographic Noise: Components and Significance

  • Radiographic Noise definition
    • Undesirable random fluctuation in optical density; grainy or uneven appearance due to insufficient primary x-rays.
    • Noise is inherent in the imaging system; lower noise improves contrast resolution.
  • Four components of Radiographic Noise
    • Film Graininess
    • Structure Mottle
    • Quantum Mottle (random x-ray interactions with the image receptor)
    • Scatter Radiation

Radiographic Image Quality Factors

  • Film factors influence quality (density, contrast, speed, latitude)
  • Processing factors (time, temperature)
  • Geometric factors (distortion, magnification, blur)
  • Subject factors (contrast, thickness, density, atomic number, motion)
  • Proper speed of screen-film combination
    • Aims to limit patient dose while producing a high-quality, low-noise radiograph.

Subject Factors and Motion Control

  • Subject factors depend on patient characteristics
    • Motion can degrade image quality; motion blur must be prevented by patient cooperation.
    • Consider patient thickness, tissue density, and anatomical shape when selecting kVp levels for optimal radiographs.

Quality Assurance (QA) Process: Standards and Criteria

  • Establish standards of image quality
    • Standards define what is considered good, poor, or reject radiographs; used to judge results.
    • In resource-scarce settings, some facilities may include a category for 'poor quality' images that still contain useful information.
  • Criteria/examples for image quality (checklist)
    • Proper collimation on all sides
    • Gonadal shield used when appropriate
    • Image density and contrast appropriate for the anatomy
    • No image degradation due to patient motion or film processing artifacts
    • Adequate display of anatomy of interest
    • Proper markers identifying left/right, hospital name, patient, date, etc.
    • Initials of the radiographer and cassette number on radiographs
  • Exam categories and applications
    • Chest X-ray, General radiography, Orthopedics, Emergency/trauma, GI studies, Urography, Pediatrics, General special procedures, Mobile X-ray, Other special X-ray exams

Film Analysis: Purpose and Procedure

  • Objectives of film analysis
    • Reduce poor and rejected radiographs; increase good-quality radiographs.
    • Periodic film analysis identifies problems and causes of poor quality.
    • It serves as a self-improvement tool and helps establish a management database.
  • Procedure for film analysis (typical workflow)
    • Collect all radiographs for a period; determine rejects, poor radiographs, and total films used.
    • With a radiologist, analyze films to identify single major problems per film.
    • Classify each film as good, poor, or reject; record problems on a film analysis form.
    • Radiologist notes problems during clinical reading; technologists collate and record.
    • Compute overall reject rate and other metrics using standard formulas.
  • Baseline data
    • Film analysis should be performed after standards are established to provide baseline data for QA/QC evaluations.

Rejection, Repeat, and Non-diagnostic Film Metrics

  • Key rates and definitions
    • Reject Rate (example formula):
      R = rac{N{ ext{rejects}}}{N{ ext{examinations}}} imes 100ig%
    • Repeat Rate (example):
      Rep = rac{N{ ext{repeats}}}{N{ ext{examinations}}} imes 100ig%
    • Non-diagnostic/poor-quality and good-quality film tallies relate to the total films used:
      ext{
      %good quality} = rac{N{ ext{good}}}{N{ ext{films used}}} imes 100ig%,
      ext{
      %poor film} = rac{N{ ext{poor}}}{N{ ext{films used}}} imes 100ig%,
      ext{
      %reject film} = rac{N{ ext{rejects}}}{N{ ext{films used}}} imes 100ig%.
  • Relationship
    • Generally, ext{Good} + ext{Poor} + ext{Reject} ≈ 100% (subject to classification scheme).
  • Practical notes
    • The overall reject rate should be monitored periodically; a typical target is to reduce poor/reject films and improve the overall quality mix.

Darkroom Quality Control (QC) and Processing

  • Role of the darkroom in QA/QC
    • The entry point for QC monitoring; many problems originate from film handling, storage, loading/unloading, and processing in the darkroom.
  • Basic darkroom QC checks
    • Cleanliness; light-tight preparation areas; avoid light leaks at doors, windows, exhausts, and pipe entry.
    • Water supply and ventilation adequacy; processing solution status.
  • Darkroom processing quality checks
    • Regular verification of processing times and temperatures; ensure solution replenishment is appropriate.

QA/QC Team and Governance Structure

  • Combined efforts required
    • All radiology staff should be engaged; a formal QA/QC committee and QA/QC team should be established.
    • Roles and responsibilities must be clearly defined and formalized by hospital orders.
  • Hospital QA/QC Team structure
    • a. Hospital chief radiologist (head of X-ray section/department)
    • b. Chief X-ray/Radiologic Technologist
    • c. Hospital physicist
    • d. Other radiologists and radiology residents
    • e. Other X-ray/Radiologic Technologists
  • Hospital QA/QC Team duties
    • Periodic film analysis; monthly film analysis reports for the QA/QC committee
    • Create or revise radiographic technique charts as needed
    • Create or revise darkroom processing charts and QC tests as necessary
    • Perform periodic QC tests of X-ray equipment and darkroom equipment
    • Maintain a room logbook with test data, procedures, sample images
    • Retain equipment manuals and brochures for reference
  • Committee operations
    • Regular meetings to discuss film analysis, QC results, problems, and corrective actions
    • Maintain minutes; hospital order formalizes the group
  • Additional program components
    • Commitment and support from radiology personnel
    • Establishment of image quality standards (good/poor/reject)
    • Monthly film analysis to identify causes of radiographic quality problems
    • Standard darkroom techniques and processing QC checks
    • Preventive maintenance and continuous education/training
    • Radiation safety program for personnel and patients

Standards, Specific QA/QC Elements, and Instrumentation

  • Departmental standards for radiographic image quality (examples)
    • Evidence of proper collimation; gonadal shielding where appropriate
    • Image density and contrast suitable for the anatomy
    • Absence of motion and processing artifacts (e.g., old screens)
    • Adequate display of anatomy of interest
    • Markers identifying left/right, hospital name, patient name, marker, date
  • Consistency across radiographic exams
    • Chest radiographs, general radiology, orthopedics, emergency/trauma, GI, urography, pediatrics, mobile radiography, other specialized exams
  • Image quality monitoring and QC timelines
    • Film analysis on a periodic basis (weekly or monthly)
    • Regular reviews and corrective actions when necessary

Darkroom Testing, Film Handling, and Safety

  • Cleaning and equipment handling (examples)
    • Film hangers: clean with hot water, identify, rinse, dry, inspect clips
    • Film viewer: cleaned with mild soap; ensure even illumination; periodic electrician checks for back-side and tubes
    • Interval timers: checked against a reference clock; replace/recalibrate if consistently wrong
    • Safelight: ensure correct bulb wattage (15 W or 25 W); adjust height to prevent fogging; verify appropriate filter
    • Environment: avoid safelight fogging; lock and control access to film storage
  • Safe handling time and safelight fog testing
    • Safelight fog testing uses unexposed films, card layers, and a densitometer to determine true safe handling time (the time after which fogging begins)
    • If safe handling time is too short, raise safelight height or increase distance or wattage; if too long, adding an additional safelight may be used but never reduce to below 4 ft above working table
  • Safe-handling time testing protocol (summary)
    • Expose layered film under safelight conditions in steps; measure density difference between exposed and unexposed layers; identify true safe handling time where the density difference first reaches 0.05

Viewboxes, Intensifying Screens, and Image Receptors

  • Viewbox/viewer quality and maintenance
    • Annual photometric testing with a photometer; target illumination ≈ 1500extcd/m21500 ext{ cd/m}^2
    • Clean surfaces to avoid reflections; replace all bulbs so that illumination is uniform; match bulbs by wattage and type
  • Image receptor components
    • Three key parts: Film, Intensifying Screens, Cassette
    • Screen characteristics and their relationship to image formation
  • Intensifying screens: purpose and function
    • Screens convert remnant x-ray energy to light photons to expose film (amplify remnant radiation)
    • In conventional radiography, less than 1% of incident x-rays interact with film to form the latent image; the screens provide the majority of exposure indirectly via light
  • Screen performance and phosphors
    • About 30% of incident x-rays interact with the screens to generate light photons
    • Rare earth phosphors (Gd, La, Y) are common; they offer high absorption (high Z) and efficient light emission
    • Modern screens use rare earth phosphors to increase speed (DQE) and reduce patient dose, but may increase image noise due to high conversion efficiency
  • Screen construction and layers
    • Four layers: protective coating, phosphor layer, reflective layer, base (polyester)
    • The base is robust, moisture resistant, radiation-stable, chemically inert
  • Spectrum matching
    • Match the emission spectrum of phosphors to the spectral sensitivity of the film and safelight
    • Calcium Tungstate produces blue light; Rare earth screens emit green light; film/screen/safelight must be spectrally matched
  • Screen speed vs spatial resolution
    • Thicker phosphor layers and larger crystals yield higher speed but lower spatial resolution; thinner layers and small crystals yield higher detail
    • The dye layer can control light spread; dyes decrease blur but may reduce speed; crystal size and concentration affect light output and speed
  • Screen contact and cassette integrity
    • Poor screen contact causes clouds/blur; common causes include worn contact felt, loose hinges, bent latches, or warped cassette
    • Screen-contact testing uses a wire mesh tool; test twice yearly or upon cassette purchase
  • Cleaning and maintenance of screens
    • Clean screens with appropriate screen cleaner; avoid alcohol; ensure screens are dry before reloading
    • Do not touch screens with bare hands to avoid artifacts
  • Additional screen problems and diagnostics
    • Dirty screens cause white spots or static on films
    • Case examples include broken hinges causing light leaks and cassette opening issues
    • Proper documentation and labeling of screens helps trace faults

Diagrammatic and Practical Screen/Cassette Tests

  • Screen/ cassette testing protocols
    • Use wire mesh or metal markers to locate faults; expose with known factors to evaluate density patterns
    • If density is inconsistent or blur is observed, identify area with poor contact or damaged screens
  • Screen/contact diagnostic tests
    • Test for poor screen contact with gel or wire mesh, mark the screen positions, and verify the density patterns after processing
  • Handling and fallbacks
    • When issues are detected (e.g., screen contact, hinges), repair or replace components using manufacturer materials

Cassette Design, Backscatter, and Spectrum Considerations

  • Cassette design basics
    • Rigid holder for film and screens with some compression to ensure close contact
    • Front: radiolucent with low absorption; back may contain metal to absorb off-axis radiation and reduce backscatter
  • Spectrum matching and film response
    • Maximum efficiency requires spectrum matching between screen emission and film sensitivity
    • mismatch leads to loss of efficiency or blurring; proper matching improves image quality

Exposure Factors, Collimation, and Radiation Safety

  • X-ray generator calibration and exposure factors
    • KVp accuracy and calibration are essential; regulated by filtered ion chambers or photodiodes
    • KVp can affect patient dose and film density; formula-like relationship exists but the exact calibration depends on the system
  • Collimation and beam geometry
    • Collimator narrows the beam to the region of interest; improves image quality and reduces patient dose
  • Key exposure factors
    • KV (kVp) determines image contrast
    • mAs (exposure amount) determines optical density (filtration and distance also influence dose)
  • Reference man concept
    • Standard reference model: height ≈ 180 cm, weight ≈ 80 kg for technique planning
  • Screen speed and exposure planning
    • Exposure factors depend on screen-film system; different brands and film processing capabilities influence the optimum kVp and mAs
  • Speed system terminology
    • Green System and Blue System refer to different phosphor families and response characteristics
  • Nominal vs actual speed
    • Nominal speed is a baseline; actual speed varies with kVp; common speeds in practice include 50, 100, 200, 400 for different systems
  • Standard radiologic technique chart
    • Each X-ray unit should have a conspicuous technique chart: patient size vs technique factors, SID, grid data, film/screen combination, shielding, and patient exposure
    • Charts should be updated when new film-screen combos or calibrations are introduced

Film-Screen System Performance: Speed, Resolution, and Noise Trade-offs

  • Film-screen speed testing and factors
    • Tests involve exposing a pair of cassettes side-by-side with old and new film-screen combos using lead sheets; multiple strips with escalating mAs are exposed
    • Process both films identically; compare densities; if corresponding strips match, speeds are equivalent; otherwise adjust exposure planning
  • Exposure factor scaling for new film-screen combos
    • The ratio by which exposure must be multiplied/divided to achieve the same film density as a baseline is defined as the speed-change factor; the goal is to determine whether the new combo is faster or slower relative to the old one
    • Procedure involves aligning test exposures and densities and deriving the speed factor from the results
  • Safe handling time and safelight considerations
    • Safe handling time is determined by densitometric difference between fogged and unfogged regions; adjust safelight placement or wattage to maintain acceptable handling times

Automatic Film Processing: System Components and QC

  • The automatic processor is the essential equipment in a radiology department
    • It dramatically reduces processing time (roughly by a factor of four vs manual development)
  • Diagnostic checks for processors
    • Besides mechanical and temperature checks, chemical checks (pH values) for developers and fixers are essential
    • Specific gravity and fixer silver levels must be monitored
  • Daily logs and trend analysis
    • Regular pH measurements (ideally daily) should be logged to identify trends and anomalies
  • Components of the automatic processor
    • Temperature control system, circulation system, replenishment system, dryer system, electrical system
  • Process control and agitation
    • Adequate agitation is required to mix chemicals, maintain uniform temperature, and ensure proper emulsion exposure
  • Maintenance issues
    • Chemical balance losses; depletion of solution levels leading to shortened contact times; potential for film damage if not monitored
  • Common problems and remedies
    • Incorrect temperatures, improper replenishment, or air exposure can degrade processing quality; routine maintenance prevents these problems

Quality Assurance in Practice: Charted Standards and Procedures

  • 8/1/20 standards and updates
    • Standards are periodically updated; material covers all sections from QA/QC governance to darkroom maintenance and processing
  • Standard radiographic technique charts
    • Each X-ray unit must have an updated technique chart reflecting patient size, SID, grid, film/screen combination, shielding, and exposure reference

Practical Notes on Film Handling, Labeling, and Storage

  • Film labeling and cassette handling
    • Labeling with a corresponding letter/number for easy identification; ensure internal ID matches labeling
    • Cleaning the cassette exterior and interior elements; absence of debris and dust reduces artifacts
  • Film storage and FIFO organization
    • Store films away from heat and light; maintain temperature range ~20extoC−25extoC20^{ ext{o}}C - 25^{ ext{o}}C
    • FIFO (oldest-first) approach to minimize film degradation and outdated stock
  • Film expiration and shelf life
    • Check expiration dates upon delivery; maintain organized stock to ensure fresh films are used

Appendices: Practical Checks and Problem Scenarios

  • Examples of screen problems and artifacts
    • Hinge issues can cause light leaks and exposure shadows on radiographs
    • Dirty or damaged screens produce white spots and static, reducing image quality
    • Poor screen contact yields cloudy/blurry areas; causes include warped cassette fronts or frames, sprung/c cracked hardware, or foreign matter in the cassette
  • Testing protocols for screen contact
    • Use wire mesh to locate faulty contact areas; identify misalignment and fabric wear
    • Verify film density patterns after exposure to ensure proper contact
  • Handling and remediation steps
    • Clean and dry screens; re-fit with manufacturer-provided tapes if needed; verify that screens are properly mounted and aligned before reloading film

Summary: Core Principles for QA/QC in Radiography

  • Establish clear image quality standards that distinguish good vs poor vs reject images, and adhere to them consistently.
  • Implement regular film analysis to identify and address root causes of poor image quality.
  • Maintain a robust darkroom QC program focusing on cleanliness, light-tightness, air/water/ventilation, and processing chemistry.
  • Ensure that a formal QA/QC committee and a dedicated QA/QC team govern policy, testing, and corrective actions.
  • Keep instrumentation and exposure systems calibrated: X-ray generator (kVp accuracy), collimation, exposure factors, and technique charts should be current and evidence-based.
  • Manage exposure factors and screen-film combinations to minimize patient dose while preserving diagnostic quality; use speed tests to quantify performance of new film-screen systems.
  • Emphasize safe handling times for films under safelight and maintain proper safelight conditions to avoid fogging.
  • Maintain meticulous documentation: film analysis results, QC test records, equipment logs, and committee minutes.
  • Integrate ethical and practical considerations: dose management, patient safety, resource-conscious practices in low-resource settings, and ongoing staff training.

extKeyformulasandvaluestoremember:ext{Key formulas and values to remember:}

  • Reject Rate: R=N<em>extrejectsN</em>extexaminationsimes100%R = \frac{N<em>{ ext{rejects}}}{N</em>{ ext{examinations}}} imes 100\%

  • (Alternate) Reject Rate (per film used): R=N<em>extrejectsN</em>extfilmsusedimes100%R = \frac{N<em>{ ext{rejects}}}{N</em>{ ext{films used}}} imes 100\%

  • Poor/Good/Total quality relations: extGood+extPoor+extReject≈100%ext{Good} + ext{Poor} + ext{Reject} \approx 100\%

  • Safe-handling time testing involves density difference threshold: the critical density difference threshold is
    \Delta D = 0.05 for fogging determination

  • Viewbox luminance target: I ≈ 1500 cd/m2I \,\approx\, 1500\text{ cd/m}^2

  • Typical temperature range for film processing environment: 20exto C≤T≤25exto C20^{ ext{o}}\,\text{C} \le T \le 25^{ ext{o}}\,\text{C}

  • Common screen materials: Calcium Tungstate (blue spectrum) vs Rare Earth phosphors (green spectrum); spectrum matching is essential for optimal film response

  • General performance notes:

    • Higher speed screens reduce required patient dose but may increase image noise and blur
    • Spatial resolution tends to decrease as speed increases; detail-oriented exams may favor slower, higher-resolution screens
    • Proper handling and routine maintenance reduce artifacts and improve overall radiographic quality

  • Standard radiologic technique chart essentials:

    • Patient size, technique factors (kVp, mAs), SID, grid data, film/screen combination, shielding, and required patient exposure
    • Charts must be updated when film-screen combinations change or equipment calibrations are updated