2. GRIDS
An X-ray grid is the part of an X-ray machine
that filters out randomly deflected radiation
that can obscure or blur an image produced
by the machine.
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3. CONTINUE
Whenever X-rays pass through matter, some of the x-ray
photons will interact with the atoms of the matter. When
taking an X-ray, may incoming X-ray photons are absorbed
by the bone, a high attenuation material, while other
tissues absorb less. This produces an image of dark and
light on the X-ray film.
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4. CONTINUE
This effect is like holding up paper to a light to see the writing on
the other side. However, absorption is not the end. As part of the
absorption, a second photon with less energy will be produced,
flying off in a different direction than the photon that was
absorbed. These “scattered” photons will create a random
grayness on the image, reducing the contrast between body
tissues, and making it difficult to read the image clearly.
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5. CONTINUE
The are five ways X-rays interact with matter. These
include photo electronic (FE), Compton Scattering (C),
Pair Production, Tomson Scattering (R), and
Photodisintegration (PD). In low energy x-rays below
100keV, only photo electronic absorption and Compton
scattering are significant.
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7. INVENTION
Dr. Gustav Bucky invented the X-ray grid in 1913. He
described it as a honey-combed lead grid. His design
was imperfect, with lead strips thick enough to appear
as lines on the X-ray image. He attempted to remove
these lines by moving the grid during X-ray exposure.
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8. PURPOSE
An X-ray grid is a filtering device that ensures the
clarity of the image on X-ray film. When an X-ray
machine sends radiation through an object,
specifically a body, the object absorbs or deflects
most of the rays.
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9. CONTINUE
Only about 1 percent of the X-rays pass through the
body on a straight line and burn an image onto the
film. The deflected X-rays can hit the film at random
angles, obscuring the image. The grid filters out
these random X-rays.
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12. GRID SHOULD BE USED FOR
Anatomical body part >10cm
With high kvp expect during mammography
Soft tissue structures to increase contrast
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13. LOCATION
In between patient and cassette (IR)
Or
The placed over the Bucky below patient table
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15. GRID RATIO
The grid ratio is a measure of the height of the
lead strip to the interspace distance, and is a
good measure of the selectivity of primary to
scatter transmission.
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17. TYPES OF GRIDS
X-ray grids are divided into four kinds based on their designs.
Parallel Type Grids
Focused Type Grids
Criss-Cross Type Grids
Tapered Type Grids
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18. PARALLEL TYPE GRIDS
A grid where the absorbing strips are parallel to
each other in their longitudinal axis. Most linear
grids are also focused (i.e. the strips are slightly
tilted, converging at a line in space (the convergent
line).
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19. CONTINUE
A non-focused linear grid has strips that are parallel when
viewed in cross-section; this is called a parallel grid. Many
X-ray tables are equipped with linear, focused grids, and
the strips in these grids are parallel with the long axis of
the table, allowing the X-ray tube to be tilted in this
direction without changing the effectiveness of the grid.
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20. FOCUSED TYPE GRIDS
A grid in which the absorbing strips are slightly angled
towards the focal spot. The grid can therefore be used only at
a specified focal distance (actually inside a narrow distance
interval around the specific distance). Otherwise, the grid will
absorb the primary radiation and parts of the film are barely
exposed. Focused grids may be linear or crossed.
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21. CRISS-CROSS TYPE GRIDS
A grid consisting of two superimposed parallel grids
having the same focusing distance. Such grids are
very efficient in removing scattered radiation but must
be arranged at exactly right angle to the beam. The use
of such grids is therefore limited.
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22. TAPERED TYPE GRIDS
A grid that the surface is tapered into the center of
grid, functioning similar to a focused grid. All of the
strips are parallel to each other, and the tapered
surface is toward the focal spot.
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23. BUCKY FACTOR
The Bucky factor is the ratio of x-rays arriving at the grid
(incident radiation), and those being transmitted through
the grid. The Bucky factor describes how much the output
of the x-ray tube must be increased in order to
compensate for the removal of incident radiation by a grid.
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24. GRID CUT OFF
Loss of primary radiation that occurs when the
image of the lead strips are projected wider
than they would be with ordinary
magnification
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