This document discusses x-ray filters, beam restrictors, grids, and grid selection for radiography. It explains that filters like aluminum and heavy metals are used to absorb higher energy photons. Beam restrictors like cones and collimators regulate the size and shape of the x-ray beam. Grids reduce scatter radiation and improve contrast. The two main grid patterns are linear and crossed grids. Grid selection depends on kVp, with 8:1 grids below 90 kVp and 12:1 grids above 90 kVp. An air gap technique is an alternative that increases focus-film distance to eliminate scatter.

1. FILTERS
DR PRAJWITH RAI

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ALUMINUM (2.5mm)↓ energy photon
↑ energy photon

3. FILTERS
• 80%. Reduction in skin exposure
• 2.5mm of aluminum --------- >70 kVp.
• Needs ↑ exposure ---------( useful radiations are absorbed )

4. Heavy metal of K-edge filters
• used to remove higher energy photons from the x-ray beam by taking
advantage of the increase in mass attenuation coefficient at the K
edge of certain elements.
• Atomic no > 60 ----- (except molybdenum )

5. K edge filters advantages
• enhance contrast for iodine and barium,
• reduce patient dose, and
• increase tube loading.

6. CONES &
COLLIMATORS

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8. x-ray beam restrictors
• Aperture diaphragms,
• Cones (cylinders), and
• Collimators.
• REGULATE
• size
• shape of x-ray beam.

9. x-ray beam restrictors
1. a smaller area of the patient is exposed
2. generate less scatter radiation
• ↓ x-ray field size === exposure factors must be ↑ ===constant film density.
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10. Collimators are the best general purpose
beam restrictors
• the x-ray field is illuminated ===accurate localization on the patient;
• x-ray field can be adjusted = ==variety of rectangular shapes and sizes.
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11. GRIDS

12. The radiographic grid
• series of lead foil strips separated by X ray transparent spacers

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14. The two basic grid patterns are:
LINEAR
• Linear focused grids converge at
a line in space called the
convergent line.
CROSSED
• A crossed grid is made up of two
superimposed linear grids that
have the same focusing distance
• Crossed grids cannot be used
with oblique techniques
requiring angulation of the X-ray
tube.

15. The three methods of evaluating grid performance:
1. Primary transmission(Tp)
2. Bucky factor (B)
3. Contrast improvement factor(K)

16. Primary transmission(Tp)
• % of primary radiation transmitted through the grid.

17. Bucky factor (B)
• incident radiation falling / transmitted radiation
• It indicates
• how much we must increase exposure factors when we change from a non
grid to a grid technique.

18. Contrast improvement factor(K)
• contrast with a grid / contrast without a grid.
• grid ratio α contrast improvement factor.
• Is the ultimate test of grid performance

19. Grid ratio / lead content and / No of lines per inch.
• When grids are constructed with many lines per inch, both the
thickness and height of the lead strips are decreased.
• These grids are thinner, and improve contrast less than grids of
comparable ratios with fewer lines per inch.

20. GRID CUT OFF
• Grid cut off is the loss of primary radiation that occurs when the
images of the lead strips are projected wider than they would be with
ordinary magnification
• The amount of cutoff is always greatest with
1. high ratio grids and
2. short grid focus distances

21. LATERAL DECENTERING
• the most common kind of grid cutoff, but it cannot be recognised by
inspection of the film.
• The films become Progressively lighter as the amount of lateral
decentering increases

22. FOCUS-GRID DISTANCE DECENTERING
• The central portion of the film is not affected, but the periphery is
light.

23. COMBINED LATERAL &FOCUS-GRID
DISTANCE DECENTERING
• It causes an uneven exposure, resulting in a film that is light on one
side and dark on the other side.

24. MOVING GRIDS
• Grids are moved to blur out the shadows cast by the lead strips.
• They eliminate grid lines from the film

25. MOVING GRIDS-DISADVANTAGES
• They are costly
• Subject to failure
• May vibrate the X-ray table
• Put a limit on the minimum exposure time because they move slowly
• increase the patient’s radiation dose

26. GRID SELECTION
• Usually 8:1 grid will give adequate results below 90kVp.
• Above 90kVp, 12:1 grids are preferred.

27. AIR GAP TECHNIQUE
• An alternative method of eliminating scattered radiation.
• The film is placed at a distance and the scatter simply misses the film.
• FFD is increased to maintain image sharpness
• Exposure factors are greater with air gaps than with grids