This document discusses three key components of x-ray imaging systems: filters, beam restrictors, and grids. It describes how filters like aluminum are used to absorb low energy rays and reduce patient exposure. It explains the three main types of beam restrictors - aperture diaphragms, cones or cylinders, and collimators - and how they define the size and shape of the x-ray beam. It also outlines the purpose of grids in removing scattered radiation to increase image contrast, and the different grid types including linear, crossed, focused, and moving grids.

1. IMAGING
KARTHIK . A
2K13MP01
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2. Outline
1. Filters
2. Beam restrictors
3. Grids
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3. 3
X-ray Filtration
• X-ray machines have metal filters inserted
into the useful beam.
• The primary purpose is the remove the low
energy beam that reach the patient and are
absorbed superficially
• Metals such as aluminum will absorb the soft
low energy rays.
• This reduces the patient exposure.

4. Types of Filtration
• There are two types of filtration:
• Inherent Filtration
• Added Filtration:
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5. Inherent Filtration
• The absorption of
X-rays by the X-ray
tube and its housing is
called inherent
filtration
• In diagnostic x-ray
tubes the glass is equal
to about 0.5 mm Al.
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6. Added filtration
• One or two mm of
aluminum is added
filtration placed in the
collimator. This
filtration is generally
placed on the mirror of
the collimator
• The minimum filtration
for tube operated above
70 kVp is 2.5 mm Al
equivalence 6
Added Filter

7. BEAM RESTRICTORS
• X Ray beam restrictors is a device that is
attached to the X-ray tube housing, to
regulating the size and shape of an X-ray
beam
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8. 3 Types of beam-restricting
devices
• Aperture Diaphragm
• Cones or Cylinders
• collimator
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9. Aperture Diaphragm
• Diaphragm consists of a sheet of lead with a
hole in the center
• The size of the hole determines the size and
shape of the X-ray beam
• The aperture can be altered to any size and
shape
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10. DISADVANTAGE
• Produce large penumbra
PENUMBRA
Away from the target[tumor]
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11. Cones or Cylinders
• It will reduce the
penumbra
• Flare of the cone is
greater than the flare of
the x-ray beam
• These systems provide
limited number of field
sizes 11

12. Collimator
• It is the best X-ray restrictors
• It defines the size and shape of X-ray field
• It attached to the tube
• Collimator consists of two sets of shutters.
Namely Longitudinal and Transverse
• Which can be moved independently
• Shutter consists of four or more lead plates
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13. Cnt……
• The collimator also has a light and mirror
arrangement, to illuminate the X-ray field
• The light bulb is positioned laterally and the
mirror is mounted in the path of the X-ray
beam at an angle 45 degree
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14. Grids
• A beam of X-ray passes through the beam is
absorbed and scattered
• The absorbed primary beam gives a useful
shadow
• Scattered radiation will tend to spoil the
shadow
• Scattered radiation will increase the noise in
the image
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15. Cnt….
• The ratio between the amount of scattered
radiation energy to the amount of primary
radiation energy at a point is called as
scattered to primary ratio(SPR)
• scattered radiation must be removed, in
order to increase the image contrast
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16. Cnt…..
• The scattered radiation can be removed by a
grid
• The grid is placed between the film and the
patient
• Cardboard, aluminium, or wood are low
attenuating materials
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17. Cnt….
• Primary radiation is parallel in direction
• Scattered radiation is non-parallel direction
Grid ratio
• The ratio of the height to the width of the
spacer between the lead strips
Grid ratio=h/b
Range =4 to 16 strip line
Densities =25 to 60 lines per cm 17

18. Types of grid
1. Linear grid
2. Crossed grid
3. Focused grid
4. Parallel grid
5. Moving grid
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19. Linear Grid
• Lead strips are parallel to each other in their
longitudinal axis
• Most of X-ray table are provided with
linear grids
• It is possible to rotate the X-ray tube along
the length of the grid
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20. Crossed Grid
• Two superimposed linear grids that have
same focusing distance
Focused grid
• Focused grid made up of lead strip that are
angled slightly so that they focus in space
• A focused grid may be linear or crossed
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21. Parallel grid
• A parallel grid is one in which the lead
strips are parallel, when viewed in a cross
section
• It can be used with small X-ray fields
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22. Moving grid
• When a focused or parallel grid is used,
each lead strip will appear on the
radiograph as a very fine line.
• These lines may spoil the information in the
film.
• These lines may be removed by moving
grid during the radiographic exposure
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23. Cnt….
• The grid may be made to move
continuously in one direction
• The grid motion is timed by the exposure
control of the X-ray machine
• The travelling period should be greater than
the exposure time
• The use of grid will always increase the
exposure, because it will absorb some of the
primary radiation 23

24. Cnt…
• In order to reduce the exposure, grid with
smaller ratios should be preferred
• Low energy grids such as 8:1
• High energy grids such as 12:1
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25. Thank you
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