QAQC

FINALS

I. ACCESSORIES IN FILM-SCREEN RADIOGRAPHY

Although digital radiography has become the dominant technology today, these accessories remain foundational. Understanding them clarifies how imaging evolved and why certain QC standards exist.

1. Viewbox (Negatoscope)

Definition

An illuminated surface used for viewing radiographic films.

Purpose

  • Provide uniform brightness to evaluate details, contrast, and density.

  • Essential for detecting fractures, lesions, and soft-tissue differences.

Key Features

  • Bright, even white light (minimum 1500 cd/m²).

  • Diffuser plate to eliminate hotspots.

  • Film clips or magnets.

Considerations / Relevance

  • Ambient light affects perception; too much brightness reduces contrast sensitivity.

  • Dirty or yellowed acrylic reduces diagnostic accuracy.

  • Evenness of illumination is critical for recognizing subtle pathology.

QC / Maintenance

  • Monthly cleaning.

  • Annual luminance uniformity test.

  • Replace dim or flickering bulbs.

2. Cassette

Definition

A light-tight container that holds film and pressed intensifying screens against it.

Purpose

  • Protect film from light.

  • Ensure good film-screen contact.

  • Provide rigid support during exposures.

Types

  • Flat cassettes

  • Curved cassettes (mammography/tomography)

  • Gridded cassettes (scatter reduction)

Important Factors

  • Must maintain perfect film-screen contact → affects sharpness.

  • Hinges/latches must prevent light leaks.

QC / Issues

  • Cassette warping → causes image blurriness.

  • Dirty screens → white spots.

  • Light leaks → fogged films.

3. Intensifying Screens

Definition

Phosphor-coated screens that convert X-rays into visible light, exposing the film.

Purpose

  • Reduce patient dose by 90–95%.

  • Provide fast imaging.

Types

  • Calcium tungstate (old)

  • Rare-earth screens (gadolinium, lanthanum phosphors – faster, more efficient)

Screen Speed

  • Slow (high detail)

  • Medium

  • Fast (low dose, less sharp)

Relevance to Exposure Factors

  • Faster screens → lower mAs → lower dose, but ↓ detail.

  • Screen-film combinations must be properly matched (blue or green sensitive).

QC Requirements

  • Screen cleaning every month.

  • Screen contact test with wire mesh.

  • Replace cracked or dead phosphor areas.

4. Grids (Accessory but essential)

Purpose

Reduce scatter radiation reaching film → improves contrast.

Types

  • Linear

  • Focused

  • Parallel

  • Crossed

  • Moving (Bucky)

Considerations

  • Grid ratio affects exposure: higher ratio → more mAs needed.

  • Misalignment causes a grid cut-off.

5. Lead Markers

Purpose

Legal requirement to indicate anatomical side (L/R) and technologist ID.

Relevance

Essential for medico-legal documentation.

6. Compression Devices / Sponges

Purpose

  • Stabilization

  • Reduce OID → improve detail

  • Reduce motion

II. RADIATION QUALITY CONTROL (QC)

Performed to ensure consistent image quality, patient safety, and equipment reliability.

Regulatory Bodies

  • FDA (sets radiation performance standards)

  • DOH / local health regulators (PH)

  • Hospital Medical Physicist → performs annual QC

  • Radiologic Technologist → daily checks

1. Peak kVp Accuracy Test

Purpose

Ensure generator delivers correct kVp → affects contrast, penetration, and dose.

Procedure

Using a digital kVp meter:

  • Expose at set kVp (60, 80, 100)

  • Meter compares actual vs displayed

Acceptance Criteria

±5 kVp from the indicated value.

If Out of Control

  • Recalibrate the generator.

  • Unsafe → equipment locked out by physicist.

2. Exposure Time Accuracy Test

Purpose

Verify timer accuracy → motion blur and density depend on correct timing.

Procedure

  • Use oscilloscope or spinning top test (for single-phase units).

  • Compare actual pulses vs expected.

Acceptance Criteria

±5% for >10 ms
±20% for <10 ms

3. mA Linearity Test / mAs Reciprocity Test

Purpose

To ensure that different mA and time combinations produce the same mAs and the same density.

Example

200 mA × 0.1 s = 20 mAs
400 mA × 0.05 s = 20 mAs
Both should produce equal film density.

Acceptance Criteria

Variation must be ≤10%.

If Failed

  • Indicates tube or generator malfunction.

4. Focal Spot Size Test

Purpose

Ensure the focal spot has not enlarged (excess heat causes blooming).
Affects sharpness and spatial resolution.

Methods

  • Pin-hole camera

  • Star-test pattern

  • Slit camera

Acceptance Criteria

Small FS: ≤50% variance
Large FS: ≤40% variance

If Failed

  • Loss of detail

  • The tube may need replacement

5. Beam Alignment Test (Central Ray Alignment)

Purpose

Confirm CR is centered and perpendicular to IR to prevent shape distortion.

Method

  • Use the beam alignment tool

  • CR and light field must match

Tolerance

±2% of SID.

6. AEC (Automatic Exposure Control) Test – One Pulse Test

Purpose

Ensure AEC terminates exposure consistently.

Method

  • Use acrylic blocks of varying thickness

  • Measure exposure time or mAs

  • Repeatability test (should be consistent)

If Out of Control

  • Overexposure or underexposure

  • AEC recalibration required by a physicist

7. Step Wedge Test (Sensitometry / Densitometry)

Purpose

Monitor film processor consistency.

Procedure

  • Expose film using an aluminum step wedge

  • Measure optical density

  • Compare with the control chart

Evaluates

  • Developer temperature

  • Chemical strength

  • Processor performance

III. STANDARD RADIOGRAPHIC TECHNIQUE CHART

A technique chart is a standardized guide indicating kVp, mAs, SID, and projection based on part thickness and patient habitus.

Its purpose:

  • Ensure consistent image quality

  • Reduce repeat exposures

  • Reduce dose

  • Provide a reference for technologists

STRUCTURE OF A TECHNIQUE CHART

1. Body Part

  • Chest

  • Abdomen

  • Skull

  • Extremities

  • Spine

2. Thickness Measurement

Measured using calipers (cm).

Thicker → more kVp or mAs
Thinner → less kVp or mAs

3. Body Habitus

  • Hypersthenic → ↑ exposure

  • Sthenic → standard

  • Hyposthenic → slightly ↓

  • Asthenic → ↓ kVp and mAs

4. Projection Type

  • AP

  • PA

  • Lateral

  • Oblique

Relevance
Different projections change OID, magnification, scatter contribution, and positioning.

RELATIONSHIPS TO OTHER FACTORS

kVp vs Contrast

High kVp → low contrast (chest)
Low kVp → high contrast (extremities)

mAs vs Density

Directly proportional.

SID (distance) effects

↑ SID → ↓ intensity → need ↑ mAs (Inverse Square Law)

Grids

Use of grid → requires ↑ mAs

Immobilization & OID

Large OID → magnification → need compensation by compression or higher SID.

PURPOSES OF A TECHNIQUE CHART

  • Standardize exposures

  • Reduce repeat rates

  • Ensure diagnostic quality

  • Control patient dose

  • Assist inexperienced technologists

EVALUATION AND ACTION (for technologists)

After every exam, evaluate:

1. Positioning Accuracy

If incorrect → repeat with explanation and corrective technique.

2. Density and Contrast

If too dark or light → adjust mAs or kVp accordingly.

3. Visibility of Detail

If blurred → assess motion / focal spot/exposure time.

4. Presence of Artifacts

Remove jewelry, clothing, and lines next exam.

5. Compliance With Technique Chart

If consistently off → chart needs revision.

ROUTINE OF CARE RATIONALE

Before Exam

  • Correct ID → safety and medico-legal

  • History taking → guides technique

  • Remove metal → prevents artifacts

During Exam

  • Proper immobilization → prevents motion blur

  • Shielding → reduces dose

  • Centering → avoids distortion

After Exam

  • Confirm image quality

  • Document exposure parameters

  • Prepare the room for the next patient