this ppt is about the working function and construction of grid

1. X-RAY GRIDS
Abhinav Sankhyan
M.MRIT

2. WHAT IS AN X-RAY GRID
 Essential in Diagnostic Imaging: X-ray grids are crucial tools used in radiography to
significantly improve the diagnostic quality of images.
 Positioning:They are placed between the patient and the image receptor (film, CR, or DR
panel) to filter scattered X-rays before they reach the detector.
 Purpose:The primary goal is to absorb scattered radiation while allowing primary (useful) X-
rays to pass through.
 Functionality:This process enhances image contrast and sharpness, especially in thick body
parts where scatter is abundant.

3. SCATTERED RADIATION
 What is Scatter? When X-rays interact with body tissues
(particularly via Compton interactions), they are deflected
from their original path.
 Random Direction: These scattered X-rays travel in
unpredictable directions and can still reach the detector.
 Image Fog: Scatter adds unwanted exposure to the image
receptor, appearing as "fog" or gray haze on the image.
 Impact: It reduces image contrast, making fine anatomical
details harder to visualize and interpret.

4. IMPACT OF SCATTER ON IMAGE QUALITY
 Decreased Contrast:The presence of scatter fills in low-
density areas with gray tones, making it difficult to
distinguish between soft tissues or detect pathology.
 Loss of Fine Detail: Subtle lesions, small fractures, or
soft tissue variations may be blurred or completely
masked.
 Diagnostic Uncertainty: Poor contrast can compromise
interpretation, increasing the risk of misdiagnosis or the
need for repeat exams.
 Clinical Significance: Particularly problematic in
abdominal, chest, and pelvic radiographs where scatter
is greatest due to larger tissue volume.

5. THE GRID’S SOLUTION – SELECTIVE
ABSORPTION
 FundamentalWorking Principle: Grids are built to absorb
scattered radiation selectively, while allowing most primary
rays to pass through.
 Structure: Composed of thin radiopaque lead strips aligned
in a specific direction, separated by radiolucent interspace
materials (e.g., aluminum, plastic, fiber).
 Primary X-rays: These rays travel in a straight line from the
X-ray tube and pass through the interspaces to reach the
image receptor.
 Scattered X-rays: Because they travel at angles, they are
more likely to strike the lead strips and get absorbed before
reaching the detector.
 Result: The image appears sharper and more contrasted,
allowing for improved diagnostic confidence.

6. TYPES OF X-RAY GRIDS
 Grid Design Variations: X-ray grids are classified
based on the orientation of lead strips and the material
used in the interspace.
 Major Types: Include linear (parallel), focused, and
cross-hatch (crisscross) grids—each engineered for
specific radiographic contexts.
 Interspace Choices: Include aluminum, plastic fiber, or
carbon fiber, which impact grid weight and
performance.
 Clinical Relevance: Grid type selection depends on
body part thickness, required image quality, and
radiographic technique.

7. LINEAR (PARALLEL) GRIDS
 Construction: Lead strips are arranged parallel to one
another and perpendicular to the grid face.
 Advantages: Easy to manufacture, lower cost, and less
sensitive to central alignment errors.
 Limitations: Susceptible to grid cutoff—especially at
image periphery when used with short source-to-image
distances (SID) or angulated beams.
 Use Cases: Best suited for non-divergent beams, or small-
field imaging where beam divergence is minimal.

8. FOCUSED GRIDS
 Design Feature: Lead strips are angled outward, matching the
natural divergence of the X-ray beam.
 Advantage: Minimizes peripheral grid cutoff, ensuring
consistent image quality across the entire detector.
 Limitation: Must be perfectly aligned with the X-ray tube’s focal
spot and used at the correct focal range (SID).
 Use Cases: Commonly used in general radiography, mobile
units, and fluoroscopy, where large fields are imaged.

9. CROSS-HATCH (CRISS-CROSS) GRIDS
 Unique Structure: Comprises two superimposed
linear grids, placed at 90° angles to each other.
 Benefit: Provides maximum scatter reduction,
regardless of the direction of scatter.
 Downside: Extremely sensitive to any X-ray tube
angulation—leads to severe grid cutoff unless
perfectly centered and perpendicular.
 Use Cases: Rare in routine radiography; used in
specialized imaging applications requiring
maximum contrast, such as high-precision studies.

10. INTERSPACE MATERIALS
 Aluminum: Most durable and common; slightly
attenuates X-rays, which increases patient dose
slightly.
 Plastic Fiber or Paper: More radiolucent, allowing
maximum primary transmission; preferred in
mammography and low-dose applications.
 Carbon Fiber: Offers excellent strength and
minimal beam attenuation, making it ideal for high-
performance, lightweight grids.
 Clinical Impact:The interspace material affects
the overall absorption, image clarity, and grid
thickness.

11. GRID RATIO
 Definition: Grid ratio = Height of lead strips (H) ÷
Distance between them (D) H/D.
→
 High Grid Ratios (e.g., 12:1 to 16:1): Remove more
scatter, but require higher exposure; suited for chest
and pelvic imaging.
 Low Grid Ratios (e.g., 5:1 to 8:1): Provide adequate
scatter reduction for thin body parts, with lower
patient dose.
 Trade-Off: Higher ratios = better image contrast, but
greater need for precise positioning and increased
dose.

12. GRID FREQUENCY
 Definition: Number of lead strips per unit length (usually per
inch or cm).
 High Frequency (e.g., > 80 lines/cm): Thinner strips = less
visible grid lines = cleaner image appearance.
 Low Frequency (e.g., < 60 lines/cm): Thicker strips = may
produce visible artifacts, especially with stationary grids.
 Importance: Particularly relevant in digital radiography, where
grid artifacts can interfere with image quality.

13. GRID MOVEMENTS & APPLICATIONS
The Problem ofVisible Grid Lines
 Artifact Risk: When using a stationary grid, the lead strips may appear as lines on
the final radiograph.
 Visibility Factors: More apparent in low-frequency grids and with digital
detectors.
 Image Distraction: Grid lines can mimic pathology or reduce diagnostic
confidence.
 Solution: Use moving grids (Bucky mechanism) to eliminate visibility.

14. STATIONARY GRIDS
 Design: Grid remains fixed during exposure.
 Advantages: Simple design, no moving parts, cost-
effective, and durable.
 Drawbacks:Visible grid lines unless high-frequency
grid is used.
 Applications: Portable radiography, trauma imaging,
and in mobile X-ray units.

15. MOVING GRIDS (POTTER–BUCKY
DIAPHRAGM)
 Mechanism: Grid moves slightly side-to-side or
oscillates during exposure.
 Purpose: Movement blurs out the lead strips,
preventing them from appearing on the image.
 Advantages: Results in uniform exposure and cleaner
images.
 Drawbacks: Adds mechanical complexity, slightly
increases exposure time, and is prone to failure.
 Applications:Widely used in table-based and wall-
stand radiography

16. RECIPROCATING GRID (BACK-AND-FORTH
MOTION)
 Movement: The grid moves linearly in one direction, usually side-to-side.
 Mechanism: Powered by a motor, it travels a few centimeters back and forth
during the X-ray exposure.
 Speed: Movement is synchronized with the exposure time to ensure lead lines are
blurred.
 Advantages:
 Effectively removes grid lines from the image
 Most common in modern Bucky systems.
 Applications: Routine radiography in fixed X-ray tables and upright stands

17. OSCILLATING GRID (CIRCULAR OR
ELLIPTICAL MOTION)
 Movement: The grid vibrates in a circular or oscillatory motion during exposure.
 Mechanism: Suspended by springs and moved by an electromagnet, allowing
smooth multidirectional motion.
 Advantages:
 Less mechanical wear than reciprocating systems.
 Smooth motion reduces chances of artifacts.
 Applications: Advanced radiographic systems, where consistent image quality is
crucial.

18. WHEN TO USE A GRID?
 Rule of Thumb: Use a grid if body part
thickness > 10 cm or kVp > 60 kV.
 Why? These settings increase scatter
production; grids reduce this and preserve
contrast.
 Avoiding Grid Overuse: For thin areas or low
kVp exams (e.g., extremities, pediatric), no
grid may be better to reduce dose.

19. APPLICATIONS IN GENERAL RADIOGRAPHY
 Chest X-ray: Grids help distinguish lung markings,
heart borders, and mediastinum clearly.
 Abdominal X-ray: Enhances contrast to visualize
organs and fluid levels.
 Spine and Pelvis: Grids prevent scatter from masking
bone structure and joint spaces.

20. OTHER KEY APPLICATIONS
 Mammography: Uses specialized high-ratio grids with very fine strips to preserve
microcalcification visibility.
 Fluoroscopy: Dynamic imaging with grids reduces scatter during real-time
procedures like angiography.
 Mobile Imaging: Grids improve quality in bedside and trauma radiography,
despite portability constraints.
 CT : Uses anti-scatter collimators, not conventional grids—but based on the same
principle.

21. GRID EVALUATION & QUALITY CONTROL
 Why Evaluate Grids?
 Maintain Quality: Ensures grid is providing maximum scatter rejection.
 Patient Safety: Helps optimize exposure, keeping dose as low as reasonably
achievable (ALARA).
 Equipment Reliability: Detects issues like grid damage, warping, or
misalignment early.
 QC Compliance: Part of institutional and regulatory quality assurance programs.

22. CONTRAST IMPROVEMENT FACTOR (CIF)
 Definition: Measures how much the grid improves image
contrast.
 Formula: CIF = Contrast with grid ÷ Contrast without grid.
 Interpretation: A higher CIF value means better scatter
rejection and image contrast.
 Used For: Comparing grid efficiency across different models
and manufacturers.

23. BUCKY FACTOR (BF)
 Definition: Indicates increase in radiation dose
required when using a grid.
 Formula: BF = Exposure with grid ÷ Exposure
without grid (mAs or dose).
 Trade-Off: Higher BF = Better image, but higher
dose.
 Optimization: Important to balance contrast gain
against dose penalty.

24. IMPORTANT GRID PARAMETERS
 Selectivity ( ):
Σ Ratio of primary radiation
transmitted to scatter transmitted; higher is better.
 Primary Transmission (Tp): How much of the
useful beam reaches the detector.
 Scatter Transmission (Ts): How much scatter slips
through the grid.
 Design Insight: Used in research and development
of advanced grid materials and patterns.

25. METHODS FOR GRID EVALUATION
 Phantom Testing: Use test objects to check contrast and uniformity under clinical
conditions.
 Dosimetry: Assess patient and entrance skin dose using meters or TLDs.
 Visual Inspection: Look for grid lines, artifacts, or alignment issues on actual
clinical images.
 Specs Comparison: Match performance with manufacturer's guidelines and
tolerances.

26. GRID CUTOFF
 Definition
 Grid cutoff refers to the unintended absorption of primary X-ray
photons by the lead strips of the grid, resulting in reduced image
density (darker or lighter areas) and potentially distorted
diagnostic quality.
 It typically occurs due to misalignment between the X-ray tube,
the grid, and the image receptor.
Causes of Grid Cutoff:
Off-Level Grid (Tilting Error)
 Occurs when the grid is tilted relative to the X-ray beam (i.e., not
perpendicular).
 Common in mobile radiography where the cassette or detector is
not flat.
 Result: Overall uniform loss of image density, especially at the
edges.

27. CONTD.
Off-Center (Lateral Decentering)
 The central X-ray beam is not aligned with the center of the focused
grid.
 Happens when the tube is shifted sideways relative to the grid’s focal
point.
 Result: One side of the image appears lighter than the other
(asymmetric cutoff).
Off-Focus (Incorrect SID)
 Using the grid outside of its recommended focal distance (Source-
to-Image Distance).
 Example: Using a 100 cm focal range grid at 130 cm or 70 cm.
 Result: Peripheral image cutoff and reduced contrast.

28. CONTD.
Upside-Down Focused Grid
 A focused grid placed backwards (lead strips diverge in
the wrong direction).
 Extremely severe form of cutoff.
 Result: Both lateral edges of the image are underexposed
(dark edges), central portion may appear relatively
normal.
5. Excessive Tube Angulation Across Grid Lines
 The X-ray tube is angled along the wrong axis (across
lead strips rather than parallel).
 Result: Partial cutoff, especially in oblique views.

29. ARTIFACTS
 Visible Grid Lines: Suggest a stationary grid, low
frequency, or mechanical failure in the Bucky
mechanism
 Moiré Pattern: Interference pattern between grid
lines and digital detector pixels; minimized by grid
frequency matching.

30. THE ROLE OF GRIDS IN PATIENT CARE
 Enhance Diagnostic Accuracy: By improving contrast and detail, grids help in
identifying subtle lesions or abnormalities.
 Aid in Disease Detection: Clearer images reduce diagnostic uncertainty,
minimizing repeat exposures.
 Justified Dose Increase: While grids raise patient dose, the gain in clinical
information makes it worthwhile.
 Standard of Care: Integral to modern imaging systems in maintaining high-quality
patient care.

31. SUMMARY
 X-ray grids selectively absorb scatter, preserving diagnostic detail.
 Their use is crucial in thicker body parts and at higher kVp settings.
 Grid types: linear, focused, and crisscross, are suited to different imaging needs.
 Moving grids help avoid visible artifacts.
 Grid ratio and frequency impact image quality and dose.
 Regular quality control ensures consistent grid performance.