production and control of scatter radiation

1. Production and control of
scatter radiation
Presenter: Sujan Karki
B.Sc.MIT 2nd year
NAMS,BIR HOSPITAL

2. Topics included
•Scatter radiation -Introduction
•Interaction of x-ray with matter
•Beam limiting devices
•Radiation grids
•Axillary method of controlling scatter radiation
•Conclusion
•References

3. Introduction
• When a photon beam interacts with matter, some
of its part get absorbed, some gets deflected to
new direction and rest of it is transmitted to
produce a radiographic image.
• The part which is deflected from its original path
to a new direction is known as scatter radiation .
• The secondary radiation which makes no
favorable contribution to the formation of image
and produce an overall blackness on the film thus
reducing the image contrast. Fig: Scatter radiation

4. Cont..
• The scattered X-ray photons -
isotropic in direction at
diagnostic energies.
• Thus, these scattered X-rays
cannot be completely removed
by the use of anti scatter grids or
energy filters.

5. Interaction of x-ray with matter
• When x-rays completely penetrate the body, there is no interaction with matter, and no
scatter or scattered radiation is formed as a result.
• When x-rays are absorbed in the body, however, their energy is “scattered,” or converted
into new scatter x-rays.
• Three types of interactions occur when radiation is absorbed by matter: coherent
scattering, Compton effect, and photoelectric effect.
• The result of either coherent scattering or the Compton effect is termed scatter radiation
or simply scatter.
• Radiation produced by the photoelectric effect is correctly referred to as secondary
radiation.
• Since more than one type of interaction takes place during radiography and the resulting
radiation is so similar, the terms are often used interchangeably.
• The interactions that produce scatter radiation in radiography occur primarily within the
patient.
• Some scattering also occurs as a result of interactions between the x-ray beam and the
tabletop and image receptor (IR), and any other matter that happens to be within the
radiation field.

6. Coherent Scattering
• Coherent scattering is also known as Thompson
scatter.
• This type of interaction takes place at relatively low
energy levels (below 10 keV).
• Figure shows the path of the x-ray photon during this
interaction. Because coherent scattering occurs in the
very low energy ranges, and outside the usual range
for diagnostic imaging, this interaction has no
significance to our daily work.
• It is mentioned here only to demonstrate that at very
low kilovolts peak (kVp) levels there is an interaction
in the body.

7. Cont..
• It is of two types
• Thompson Scattering : single electron involved in the
interaction.
• Rayleigh Scattering: Co-operative interaction of all the
electrons of an atom .
• No Ionization --- why??? Because ,no energy transfer .only
change of direction .
• Coherent Scattering accounts for less than 5% of all photons
interactions and is of minor concern in diagnostic radiology.
• Coherent scattered photons travel in a forward direction.
• At 70 kVp, a few percent of the x-rays undergo coherent
scattering, which contributes slightly to image noise, the
general graying of an image that reduces image contrast.

8. Compton scattering
• The Compton effect occurs at energy levels
throughout the diagnostic x-ray range of kVp.
• The incoming x-ray photon interacts with an
outer orbital electron of an atom, removing it
from the atom (ionization), and then proceeds
in a different direction.
• The majority of the photon’s energy is
converted into a new photon of scatter
radiation.
• This new photon has less energy than the
incoming primary beam photon and therefore
a longer wavelength.

9. Direction and effects of Compton scattering

10. Cont..
•Compton scatter travels in all
directions.(including 180 degrees from
the incident x-ray).
• If it is directed back toward the x-ray
tube, it is termed backscatter.
• Most of the photons that are scattered
will scatter in a more forward direction.
• As the kVp is increased, Compton
interactions are increased.

11. Photoelectric effect
• In a photoelectric interaction, the incoming photon from the primary
beam collides with an inner orbital electron of an atom.
• The photon is totally absorbed in the process and creates an
absorbed dose in the patient.
• The electron’s departure leaves a “hole” in the orbit, which is filled
by an electron from an outer shell.
• The difference in binding energy between the two shells is emitted
as a new x-ray photon.
• This photon is referred to as a characteristic photon and is
considered secondary radiation because it is radiation actually
produced in the body.
• Its energy will be less than that of the primary photon.
• Photoelectric interactions are less prevalent in the diagnostic
energy range than Compton interactions.

12. Cont…
• The likelihood of a photoelectric interaction is determined by both the kVp
level and the electron-binding energy of the atom in which the interaction
occurs.
• Because no part of the energy of the incoming photon exits the atom,
photoelectric interactions are sometimes referred to as true absorption.
• In this text, references to scatter also apply to secondary radiation formed by
the photoelectric effect.
• As kVp is increased, photoelectric effect is decreased.
• Note, this is the opposite of the Compton effect.
• In the diagnostic range of kVp used (50 to 100 kVp) the majority of radiation
interactions with the body are Compton interactions.

13. Radiographic effect of scatter radiation
• The production of scatter radiation during an
exposure results in fog on the radiograph.
• Fog is unwanted exposure to the image.
• It does not strike the IR in a pattern that represents
the subject, and it contributes nothing of value to the
image.
• This fog produces an overall increase in radiographic
density. The result is also a reduction in radiographic
contrast
• Although increased density in the darker areas of the
image is scarcely noticeable, areas that would
otherwise be bright or white will instead be gray
because of the fog.
• In other words, scatter radiation creates fog that
reduces both contrast and the visibility of detail.

14. Causes of increase in scatter radiation
Increase in kvp
Increase in patient
thickness
Increase in field size

15. KVp
• Affects the penetrability of the beam.
• Higher kVp, more photons go through patient to the IR, less absorbed
by patient, higher scatter and less contrast on image
• Lower the kVp, increase in dose absorbed by patient, less fog on film,
more contrast image.
• As x-ray energy increases, the relative number of x-rays that undergo
Compton Scattering increases.
• The absolute number of the Compton interactions decrease with
increasing energies but the number of photoelectric interactions
decreases more rapidly.

16. cont
• At 50 kVp 79% photoelectric, 21%
Compton & less than 1%
transmission.
• At 80 kVp 46% photoelectric, 52%
Compton & 2% transmission
Fig: The relative contribution of photoelectric effect and Compton
scattering to the radiographic image.

17. Field size
• Has a significant impact on scatter radiation.
• Field size is computed in square inches or square cm
• As field size increases, intensity of scatter radiation also
increases rapidly. Especially during fluoroscopy
• The relative intensity of the scatter varies more when the field
size is small than when the field is large.
• When the field size is reduced, the resulting reduction in
scatter will reduce the density on the image.

18. Cont..
• The mAs must be increased to
maintain density.
• The reduced scatter will improve
contrast resolution resulting in
improved image quality.
• To change from a 14” x 17” to a 10”
x 12” increase mAs 25%.
• To change from a 14” x 17” to a 8” x
10” increase mAs 40%. Fig: Collimation of the x-ay beam results in
less scatter radiation.

19. Part or patient thickness
• The relative intensity of scatter radiation increases with increasing
thickness of the anatomy.
• There will be more scatter for a lumbar spine film compared to a
cervical spine film.
• As tissue thickness increases, more of the rays go through multiple
scattering.
• Normally body thickness is out of our control but we can change the
method of imaging to improve image quality.

20. Part or patient thickness

21. Does patient thickness affects the image
contrast…?
Fig a Fig b

22. Beam restriction and scatter radiation
• In addition to decreasing patient dose, beam-
restricting devices reduce the amount of scatter
radiation that is produced within the patient,
reducing the amount of scatter the IR is
exposed to, and thereby increasing the
radiographic contrast.
• The relationship between collimation (field
size) and quantity of scatter radiation is
illustrated in figure.
• As stated previously, collimation means
decreasing the size of the projected field, so
increasing collimation means decreasing field
size, and decreasing collimation means
increasing field size.

23. Cont..
• It is the responsibility of the radiographer to limit the x-
ray beam field size to the anatomic area of interest.
• Beam restriction serves two purposes:
1) limiting patient exposure and
2) reducing the amount of scatter radiation produced
within the patient.

24. Types of Beam-Restricting Devices
• Several types of beam-restricting devices, which differ in sophistication and
utility, are available.
• All beam-restricting devices are made of metal or a combination of metals
that readily absorb x-rays.
• Also known as beam limiting device and includes
1) aperture diaphragm
3) cones and cylinders
4) various aperture collimator

25. Aperture Diaphragms
• The simplest type of beam-restricting device is the aperture diaphragm.
• An aperture diaphragm is a flat piece of lead (diaphragm) that has a hole
(aperture) in it.
• Commercially made aperture diaphragms are available, or hospitals make
their own for purposes specific to a radiographic unit.
• Aperture diaphragms are easy to use.
• They are placed directly below the x-ray tube window.
• An aperture diaphragm can be made by cutting rubberized lead into the size
needed to create the diaphragm and cutting the center to create the shape and
size of the aperture.

26. Aperture Diaphragms
Typical trauma radiographic
imaging system

27. Cont..
• Although the size and shape of the aperture can
be changed, the aperture cannot be adjusted
from the designed size, and therefore the
projected field size is not adjustable.
• In addition, because of the aperture’s proximity
to the radiation source (focal spot), a large area
of unsharpness surrounds the radiographic
image.
• Although aperture diaphragms are still used in
some applications, their use is not as widespread
as other types of beam-restricting devices.

28. Cones and Cylinders
• Cones and cylinders are shaped differently but they have
many of the same attributes.
• A cone or cylinder is essentially an aperture diaphragm that
has an extended flange attached to it.
• The flange can vary in length and can be shaped as either a
cone or a cylinder.
• The flange can also be made to telescope, increasing its
total length .
• Similar to aperture diaphragms, cones and cylinders are
easy to use.
• They slide onto the tube, directly below the window.
• Cones and cylinders limit unsharpness surrounding the
radiographic image more than aperture diaphragms do, with
cylinders accomplishing this task slightly better than cones
as shown in Figure .

29. Cont..
• However, they are limited in terms of available
sizes, and they are not interchangeable among tube
housings.
• Cones have a particular disadvantage compared
with cylinders.
• If the angle of the flange of the cone is greater than
the angle of divergence of the primary beam, the
base plate or aperture diaphragm of the cone is the
only metal actually restricting the primary beam.
• Therefore, cylinders generally are more useful
than cones.
• Cones and cylinders are almost always made to
produce a circular projected field, and they can be
used to advantage for particular radiographic
procedures

30. Improved contrast resolution

31. Collimators
• The most sophisticated, useful, and accepted type of
beam-restricting device is the collimator.
• Collimators are considered the best type of beam-
restricting device available for radiography.
• Beam restriction accomplished with the use of a
collimator is referred to as collimation.
• The terms collimation and beam restriction are used
interchangeably.
• note(Collimator misalignment should be less
than 2% of the SID used, and the
perpendicularity of the x-ray central ray must be
less than or equal to 1 degree misaligned.)

32. • A collimator has two sets of lead shutters.
• Located immediately below the tube window, the
entrance shutters limit the x-ray beam much as the
aperture diaphragm would.
• These shutters consist of longitudinal and lateral leaves
or blades, each with its own control.
• This design makes the collimator adjustable in terms of
its ability to produce projected fields of varying sizes.
• The field shape produced by a collimator is always
rectangular or square, unless an aperture diaphragm,
cone, or cylinder is slid in below the collimator.
• Collimators are equipped with a white light source and
a mirror to project a light field onto the patient.
• This light is intended to indicate accurately where the
primary x-ray beam will be projected during exposure.

33. Positive beam limiting devices
• Misalignment of the light field and x-ray beam can result in collimator cutoff
of anatomical structures.
• Today nearly all light-localizing collimators manufactured in the United
States for fixed radiographic equipment are automatic.
• They are called positive beam–limiting (PBL) devices.
• When a film-loaded cassette is inserted into the Bucky tray and is clamped
into place, sensing devices in the tray identify the size and alignment of the
cassette.
• A signal transmitted to the collimator housing actuates the synchronous
motors that drive the collimator leaves to a precalibrated position, so the x-ray
beam is restricted to the image receptor in use.

34. Is there any difference in these two pictures
regarding radiographic contrast and image noise?
Fig a
Fig b

35. Two factors determine the amount of energy
retained by deflecting photon
• Initial energy
• Deflecting photon

36. Filters
• Filtration is basically a process of shaping the x-ray beam to
1) increase the amount of useful photons
2) decrease the low energy photons
• This also decreases the patient dose and occupational dose

37. How filtration works
• When exposure is done both high and low energy xrays are produced
• When these xrays photons interact with the human body only the high
energy photons penetrates the body, while low energy photons are
absorbed in the body, hence increasing the patient radiaition dose.
• Filtration basically absorbs the low energy photons from the beam and
hence increases the image contrast.

38. Comparison of the radiograph

39. Levels of filtration
•Inherent filtration
•Added filtration

40. Inherent filtration
•The absorption of the low energy x-ray photons by the x-ray
tube components itself is known as the inherent filtration.
•Glass housing, metal enclosure and the assembly oil is
responsible for inherent filtration.
• Inherent filtration of a tube is measured in ALUMINIUM
EQUIVALENT.
• It is basically the amount of aluminum required to absorb
the same radiation which the tube material was absorbing.
•Inherent filtration is generally between 0.5-1.00mm of
aluminum equivalent.

41. Diagram of inherent filtration
Position indicating
device

42. Added filtration
• Added filtration is a result of any beam absorber which is
placed in the path of the xray beam, this absorber absorbs
the low or high energy photons.
• Ideally an added filter should absorb all the low energy
photons and let the high energy photons pass through it.
• But no such material exists.
• SOLUTION- we always use added filters mostly in a
group of Aluminium(13) + Copper(29).

43. Cont..
•They are arranged as the high at. No.(COPPER) element
faces the x-ray tube while the other(ALUMINIUM) one
faces the patient.
• Most of the filtration is done by copper.
•They can't be used separately.
• Patient radiation dose as well as the image contrast is
reduced.
•This combination of two layers of filters is also known as
COMPOUND FILTERS.
• It also increases the tube loading.

44. Added filter

45. Wedge filter
• Wedge filters are mostly used at places where
the body part to be radiographed varies greatly
in densities.(thick from one side and thin from
another side)
• Wedge filters are like the shape of a wedge ,
the thin part is placed under thick body part
while thick part is placed under thin body part.
• Result is that ,beam attenuation by thick part is
more hence less radiation reaches the part and
beam attenuation by thin part is less hence
more radiation reaches thick part.
• Therefore a radiograph of uniform density is
achieved.

46. Sources of scatter radiation
• Patient himself
• Glass walls of x-ray tube
• Tabletop
• Cassette
• Back scatter from floor
• Back scatter from wall

47. Characteristics of scatter radiation
• More oblique in nature
• Produced by matter in all direction
• Less energy than primary beam
• With increase in energies energy of primary radiation more scatter in
forward direction
• Amount of scatter depends on
1) volume of tissue
2) thickness of patient
3) kvp used

48. Effects of scatter radiation
• Increase overall density of the film which is not useful in
production of image thus produces of fog
• Reduces contrast
• Reduce light transmitting ability of film
• Result in the formation of noise

49. Solution to decrease scatter radiation
• Various devices to reduce scatter
• Filters
• Aperture diaphragm
• Cones and cylinders
• Collimators
• Radiographic grids

50. Control of scatter radiation
• Generally two types of devices can be used to reduce scatter radiation
reaching image receptor
• Before Patient
• On Patient
• After Patient
Beam Restrictors
Compression
Grids

51. Axillary methods to control scatter radiation
• There are two auxiliary methods to control the scattered radiation :
1)Air Gap Technique
2)Compression Technique
• In conventional film screen system, the filtration effect of screen
against the scatter and the harder, primary photons are intensified more
than the softer, scattered ones.
• Being the film itself more or less equally sensitive to both scattered and
primary photons, this leads to a reduction on the relative effect of
scattered radiation on the film.
• The lead lined at the back of the conventional as well as modern
cassette reduces the effect of back scattered radiation from the Bucky
and ground to the film or IR.

52. Compression bands
• It reduces the amount of scatter by diminishing the volume of tissue
through which x-ray passes
• It displaces the adipose tissue side ways thus reducing the volume of
the part to be x-rayed and lowers the kilovoltage to be used.
• Advantage
1) It acts as a immobilizing device.
2) helps in the reduction of the scatter radiation thus improving the
contrast.

53. Compression
•Reduces OID
•Improves spatial resolution
•Improves contrast resolution
(reducing noise and fog)
•Reduces patient dose

54. Is patient thickness something the
radiographer can control?
• Normally no
• But compression devices can be used in certain
situations which reduces patient thickness and
bringing the object closer to the IR, and therefore
results in better spatial resolution and contrast
resolution and also lesser exposure factors and patient
dose

56. Air gap technique
• The air gap technique is an alternate scatter reduction method and can
be used instead of a grid.
• It uses an increased OID to reduce scatter reaching the image receptor.
• This technique is used in lateral C-Spine and chest radiographs.
• Since the patient is the source of scatter and the increased OID causes
much of the scattered radiation to miss the image receptor.
• This reduces scatter and to improve the contrast of the image.
• A major disadvantage of the air gap technique is the loss of sharpness,
which results from the increased OID.
• The air does NOT filter out the scattered x-rays.

57. Air gap technique
• An OID of at least 6 in (15 cm) is
required for effective scatter reduction.
• A longer SID is utilized with a small focal
spot size to reduce the magnification.,
• With the increased SID, the mAs must be
increased to maintain radiographic
density.
• When air gap technique is used the mAs
is increased approximately 10% for every
centimeter of air gap.
• The technique factor usually are about the
same as those for an 8:1 grid ratio.

58. Cont..
• The air gap technique technique is not normally as effective
with high kVp radiography, in which the direction of the
scattered x-ray is more forward.
• At the tube potentials below approximately 90kVp, the
scatter x-rays are directed more to the side ,therefore they
have a high probability of being scattered away from the
image receptor.

59. Scatter removal by air gap technique

60. Radiation grids
• Rapid adaption of new technology and device.
• Dr. Gustave Bucky in 1913 demonstrated scatter
radiation and it remedy by using grids, working in the
field of radiology.
• It is a radiographic accessory which is designed to
minimize the effect of scatter radiation reaching the film.
• Grid is composed of thin strips of lead which are
separated from each other by interspace material which is
penetrable by primary beam.
• Grids are commonly used in radiography, with grid ratio
available in even numbers, such as 4:1, 6:1, 8:1, 10:1 or
12:1.
• breast (mammography): uses 4:1 grid ratio
• Grid ratio of 8:1 is generally used for 70-90 kVp
technique and 12:1 is used for >90 kVp technique.
Fig: X-RAY GRID
PARALLEL 40 LINES
RATIO 8:1 ,3 mm thick

62. • The appropriate acquisition techniques, when using
digital systems, depends on many factors including
the image quality performance of the detector, grid
performance, the scattering characteristics of the
patient, imaging geometry, image processing, and
the degree to which grid alignment can be assured.
• Appropriate choice of the relevant “digital” Bucky
factor is necessary to obtain the best quality
diagnostic image at the lowest possible patient
dose.
• Image quality was improved for 80% of patients
when their images were captured with the grid
without increasing the patient dose.(Foos, 2012)

63. Radiographic grid is recommended for :
• Anatomical part more than 10 cm
• With high kvp (Not always mammo)
• Soft tissue structures to increase
contrast
• Structure affected by pathological
condition that would increase scatter
production

64. Ideal grid
•It is the which absorbs all scatter radiation and allows
the primary radiation to pass through, but no grid is
ideal.
• Uses:
1) abdomen
2) skull
3) spine
4) pelvis
5) penetrating chest x-rays

65. Cont…
• There are two basic types of grids:
1)Focused
2)Unfocused
3)Moving grid
• A grid is unfocused when all the lead strips are parallel to each other and
perpendicular to the grid surface, provides more freedom i.e. distances
can be varied.
• A grid is focused when all the lead strips except those in the center are
inclined at an angle towards the center (they are actually on radius of a
circle whose center is the focal spot of the tube when the correct distance
is used).
• Moving grids (also known as Potter-Bucky grids): eliminates the fine grid
lines that may appear on the image when focussed or parallel grids are
used

66. Types of grids and their working principle
Fig:Focused grid Fig:Parallel grid and grid cut- off of scattered as well as primary
radiation.

67. High transmission cellular grid (HTC)
• Reduces scatter radiation in the two
directions
• Grid strips-copper
• Interspace material-air
• Physical dimensions-3.8:1

68. Parameters of grid
• Grid ratio
• Grid frequency
• Nature of interspace material
• Lead contents

69. Grid ratio
• It is defined as the ratio between the
height of lead strips and distance
between two adjacent strips.
It is the parameter which determines
the ability of a grid to remove scatter
radiation.
• It measures the narrowness of the slits.
• It determines the extent to which
obliquely moving scatter radiation is
absorbed.

70. Grid frequency
Number of grid lines per inch or centimeter
Usually range from 25 -45 lines per cm
In mammographic grids have frequencies of 80 lines/cm 4:1 or 5:1 grid
ratio of grid
High frequency grids
More grid strips
High radiographic technique
Higher patient dose
No significant grid lines on the image

71. Radiographic Grids
• The higher the grid ratio the more exposure is required.

72. Comparison between two types of interspace
material

73. Advantages and disadvantages of aluminum
•Advantages
1)Non-hydroscopic – does not absorb moisture as plastic fiber does.
2)Easy to manufacture as it can be roll into sheets of precise thickness.
3)Provide selective filtration of scattered x-rays not absorbed in grid
strips.
4)Produce less visible grid lines on the radiograph .
•Disadvantages
1)Increase the absorption of primary x rays (low kVp)
2)Higher mAs and higher patient dose
3)For low kVp , patient dose may be increased by 20%

74. Dose reduction by carbon fibers
• Typically the dose can be reduced by 3-15% by changing the
table top, 6-12% by changing the front of the film cassette
and 20-30% by using a grid with carbon fibre covers and
fibre interspace. The higher cost of carbon fibre components
can normally be justified by such dose savings. An indication
of the absorption of all such components should be provided
by manufacturers.(A P H ufton March 1986 BJR)

75. Bucky factor
• Ratio of the incident radiation
falling on the grid to the transmitted
radiation passing though the grid.
• Indicates actual increase in exposure
due to grids presence
• Due to attenuation of both primary
and secondary radiation
• Higher the grid ratio =higher bucky
factor.
• Bucky factor(B) is also known as
image factor.

76. Contrast improvement factor
• Gridratio, however, does not reveal the ability of
the grid to improve image contrast.
• This property of the grid is specified by the contrast
improvement factor (k).
• A contrast improvement factor of 1indicates no
improvement.
• Most grids have contrast improvement factors of
between1.5 and 2.5.
• In other words, the image contrast is approximately
doubled when grids are used.

77. Grid cutoff
• Loss of primary that occurs when the image of the lead stripes are
projected wider than they would be with ordinary magnification
• Types of grid cutoff
• Focused grids used upside down
• Lateral decentering
• Distance decentering
• Combined decentering

78. Image quality dur to the misalignment of grid
Mobile radiograph of proximal femur and hip, showing comminuted fracture of left
acetabulum. A, Poor-quality radiograph resulted when grid was transversely tilted far
enough to produce significant grid cutoff. B, Excellent-quality repeat radiograph on the
same patient, performed with grid accurately positioned perpendicular to central ray.

79. Focussed grid upside down
• Dark band of central exposure
• Severe cut-off at periphery
• Crossed grid-small square at the centre is exposed

80. Lateral descentering
• Results from the x-ray tube being positioned lateral to the
convergent line but at the correct focal distance
• Probably most common type of grid cutoff
• Uniform loss of radiation over entire film
• Uniformly light radiograph
• Not recognizable characteristics

81. Lateral descentering
• Also occurs when grid is tilted
• Magnitude depends upon
1) grid ratio
2) focal distance
3) amount of descentering
Lateral decentering is the significant problem in portable
radiography
Becouse exact centering is not possible
Minimizing lateral descentering
1) low ratio grids
2) long focal distances

82. Far focus-grid decentering and near focus-
grid centering
• Cut off at periphery
• Dark centre
• Cutoff proportional to
1) grid ratio
2)decentering distance

83. Combined lateral and focus decentering
• Most commonly recognized
• Uneven exposure
• Film is light on one and dark on other side

84. Grid information

85. Artifacts in grid (moiré effect)
vertical banding pattern artifact

86. Radiation safety
Whenever possible, the radiographer should stand at least 6 ft (2 m) from the patient and
useful beam. The lowest amount of scatter radiation occurs at a right angle (90 degrees) from
the primary x-ray beam. A, Note radiographer standing at either the head or the foot of the
patient at a right angle to the x-ray beam for dorsal decubitus position lateral projection of the
abdomen. B, Radiographer standing at right angle to the x-ray beam for AP projection of the
chest. IR, image receptor.

87. Conclusion
• Controlling the amount of scatter radiation produced in a patient and ultimately
reaching the image receptor (IR) is essential in creating a good-quality image.
• Scatter radiation is detrimental to radiographic quality because it adds unwanted
exposure (fog) to the image without adding any patient information.
• Digital IRs are more sensitive to lower-energy levels of radiation such as scatter,
which results in increased fog in the image.
• Increased scatter radiation, either produced within the patient or higher-energy
scatter exiting the patient, affects the exposure to the patient and anyone within
close proximity.
• Beam-restricting devices decrease the x-ray beam field size and the amount of
tissue irradiated, thereby reducing the amount of scatter radiation produced.
• It should be noted that grids do nothing to prevent scatter production; they merely
reduce the amount of scatter reaching the IR.

88. References
• Sehlawi : Rad 206 p11 Fundamentals of Imaging - Control of Scatter Radiation
• The use of carbon fibre material in table tops, cassette fronts and grid covers:
Magnitude of possible dose reduction Article in British Journal of Radiology
• MYTH BUSTER: “DOSE INCREASES WITH CR & DR SYSTEM GRID
ALIGNMENT”July 24, 2012
• Radiologic Science for Technologist (Physics, Biology and Protection) by
Stewart C. Bushong, 10th Edition.

89. Questions
•How does the scatter radiation effects the radiographic
image?
•What are the factors that contribute to an increase in
scatter radiation ?
•What do you understand by positive beam limiting
device?
•What are the axillary method to control scatter radiation?
•Why is filter used in x-ray tube and what are its type?