X-ray Filtration

1
X-ray Filtration

• When the x-ray beam is produced, many energies of
  photons exist. Many are of such low energies that
  they will offer nothing to the production of the
  radiograph.
• Metals such as aluminum will absorb the soft low
  energy rays.
• This reduces the patient exposure.

2
X-ray Filtration

• The leaded glass window of the tube acts as
  Inherent Filtration.
• Aluminum is attached to the mirror in the
  collimator. This is called Added Filtration.

3
X-ray Filtration

• Total Filtration required by Federal and State
  Law is 2.5 mm of Aluminum equilivant for tube
  that operate at or above 70 kVp.
• This filtration hardens the beam

4
Compensatory Filters

• Compensating Filters are used to equalize
  exposure when there is varying densities in the
  area being radiographed.
• Filters are placed in the less dense area

5
Compensatory Filters

• The aluminum filter will block the collimator
  light but will let the x-ray pass through and a
  reduced level based upon the thickness of the
  filter.

6
Compensatory Filters

• Filters will impact both the density and the
  contrast of the image due to the reduction of
  photons.
• Filtration decreases density and contrast.

7
Compensatory Filters

• Filters are used when taking the thoracic spine,
  A-P full spine and on female patients on the
  lateral lumbar spine.

8
Compensatory Filters

• Filters can also be used as gonadal protection on
  female patients. The exposure to the ovaries and
  uterus is reduced when this filter is used on
  the A-P Full Spine or Lumbopelvic

9
Heart Shaped Filter

• The filter is used to reduce exposure to the
  ovaries and uterus.
• Often we eliminate the filter by turning the
  patient PA. The bone of the pelvis will absorb
  50 of the exposure.

10
Use of Compensating Filter

• The image on the left has a filter used to
  equalize exposure over the entire thoracic spine.
• The image on the right was taken without a
  filter. The upper spine is poorly visualized.

11
Filters Affect Contrast and Density

• Typically on female patients, the upper lumbar
  spine is over penetrated unless filtration is
  added to reduce the exposure above the iliac
  crest.

12
Filters do improve the image

• It not over expose the fingers on this lateral
  hand, a filter was used to reduce the exposure of
  the fingers.

13
Filters equalize exposure

• A filter above the crest would reduce exposure to
  the lumbar spine to improve visualization.
• Filters often used on female lateral lumbar views.

14
Observations

• 1. Compare the two images. Is the density and
  contrast the same at the top of the films?
• The film with the filter is more uniform in
  density. The film without the filter is
  overexposed.

15
Observations

• 2. Do you see any area where there was no
  exposure?
• No. The filter blocked the light but not the
  x-rays.
• 3. Did the filter absorb all the photons?
• No. It reduced the exposure but did not eliminate
  it.

16
Anode Heel Affect

• During the exposure, some of the radiation is
  actually absorbed by the anode.
• This results in about a 20 decrease in density
  at the upper range of collimation on the anode
  side of the image.
• The anode should be up when the equipment is
  installed.

17
Anode Heel Affect

• In medical recumbent radiography, the patients
  head may be positioned toward either end of the
  table.
• During erect radiography, this is not possible
  since we can not hang them from their feet. For
  this reason, the anode heel affect is of less
  importance in Chiropractic Radiography.

18
Collimation

• Collimation is the restriction of the primary
  beam.
• It is our best tool to reduce patient exposure.

19
Collimation

• Collimation must be slightly less than film size.
• Or
• To the area of clinical interest, which ever is
  smaller

20
Collimation

• When we go from a large film to a small film with
  proper collimation, the amount of radiation
  available to produce the image is reduced.
• The scatter radiation is reduced, improving
  contrast of the image and patient exposure.

21
Affects of Collimation on Density

• Collimation reduces scatter and primary
  radiation.
• This causes the image to be light.

22
Collimation

• If we collimate to a smaller area and do not
  adjust exposure, the density of the image
  decreases.
• From 14 x 17 to 10 x 12 increase mAs 1.25 times.
• From 14 x 17 to 8 x 10 increase mAs 1.4 times.

23
Collimation

• Left Image no increase in mAs Right image
  increased 1.4 times

24
Observations

• 1. Is there a difference in the density of the
  images comparing the 14 x 17 to the 8 x 10 Image
  A?
• Yes Image A is under exposed compared to the 14 x
  17.
• 2. Is the density of image 8 x 10 (C) comparable
  to the 14 x 17?
• Yes

25
Observations

• 3. Do you see an increase or decrease in detail
  between the 14 x 17 and Image C?
• Yes The contrast is better , making the image
  sharper.

26
The End

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