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 patient’s 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. Other Factors that Impact Detail • The Relative Speed Value of the screens and film used. • Screen and Film Contact • Patient motion • Processing of Image

27. Relative Speed Value of Film System • The higher relative speed value systems will produce less sharp images. • The size of the grains on the film and phosphors are larger on high speed systems. This results in less detail. • High speed systems need less radiation to produce the image. They have more quantum mottle.

28. Cassettes • Black border Kodak Lanex Regular Cassettes are 400 speed and used for spine and general radiography. • Grey Border Kodak Lanex Fine Cassettesor Extremity Cassettes are 80 speed and used for non-Bucky small extremity films.

29. Screen Film Contact • The film must be in full contact with the intensifying screens. • If the screens are worn, dirty of not in contact with the film, detail will be reduced.

30. Screen Film Contact • This is poor screen film contact.

31. Poor Screen Contact • There is a loss of detail in the thoracic and lumbar spine due to poor screen contact. • This was a new cassette.

32. Poor Screen Contact • Note the blurry image in the spine but sharp image of the ribs. • The screens were not in proper contact in the middle of the cassette due to a bow in the cassette back.

33. Dirty or Damaged Screens • Dirty or damaged screen will cause white spots on the image.

34. Dirty or Damaged Screens • The multiple white spots are the result of worn out screens. • Improper cleaning is the likely cause. Never use alcohol to clean screens.

35. Motion • If the patient moves or fails to hold their breath, the image will be blurry. • Large patient may need to have films taken with the large focal spot.

36. What Is Wrong with this Picture? • Is this image under exposed or over exposed? • Did the patient move? • This image is under developed. The technical factors were correct.

37. What Is Wrong with this Picture? • The temperature of the developer was too low resulting in this underdeveloped image. • After the temperature was corrected, the films came out fine.

38. What Is Wrong with this Picture? • Films were taken and processed before the processor had warmed up to proper operating parameters. • Processing impacts both density and contrast of the image.

39. Methods Used to Reduce Radiation Exposure • High frequency radiographic machines reduce exposure 35% compared to single phase. • Use as high kVp as possible that will give adequate contrast. • Measure the patient and used good technique charts.

40. Methods Used to Reduce Radiation Exposure • Use high speed film and cassettes for general radiography. • Collimate the beam to the area of interest or smaller than film size. • Use gonadal protection unless it would block the view. • Use fixed kVp Technique Charts

41. Methods Used to Reduce Radiation Exposure • Use compensating filters to reduce exposure to less dense areas of the body. • Use Quality Control to assure the machine is operating properly. • Practice proper positioning protocols to avoid retakes. • Consider the risks & benefits before x-rays.

42. Special Precautions for Females between 10 and 50 years old. • We must make sure the patient is not pregnant before exposing the patient to ionizing radiation. • Always ask is there is a potential for pregnancy and have the patient sign the request documenting that they were asked.

43. Special Precautions for Females between 10 and 50 years old. • The ten to fourteen days rule. The safest time to perform an x-ray on a female of child bearing years is between 10 and 14 days from the onset of menses. • Risks are reduced when the exam is farther away from the ovaries. A c-spine is safer than a lumbar spine exam.

44. Methods Used to Lower Exposure Females between 10 and 50 years old. • Positioning Lumbar films P-A: The pelvis bone will absorb 50% of the exposure. • Special shields used to protect breast tissue on Full spine exams. • Filter used to reduce exposure to the ovaries for A-P full spine.

45. mAs controls Density. Increase mAs, increase density kVp controls Contrast High kVp= Low Contrast = Longest Scale= Most scatter= Lowest exposure Low kVp= High Contrast= Shortest Scale= Least Scatter = Highest Exposure Small Focal Spot gives the highest geometric resolution.. Small Focal Spot has lowest mA settings Physics Review

46. Filters are used to compensate for differences in tissue density. They affect both density and contrast. Short SID will have the most magnification distortion. Long SID can compensate for increased OID Focal spot size is less important with long SID. OID should be as small as possible. Physics Review

47. Tube angulation is used to move overlying structures and to get the beam perpendicular to angled structures. Cephalad refers to angles toward the head. Required angle is added to 90° for erect radiographs. Caudal refers to angles towards the feet. Required angle is subtracted from 90° for erect radiography. Physics Review

48. If the beam is not centered to the area of interest, there will be shape distortion. If the body part is angled in relation to the film or the beam, there will be shape distortion. Grids are used to control scatter radiation. High frequency and ratio grids will remove the most scatter radiation. Physics Review

49. Any misalignment of a focused grid will result in grid cut-off. Collimation is our best tool for reducing radiation exposure to the patient. Collimation must be to slightly less than film size or the area of clinical interest, whichever is smallest. Collimation reduces scatter and primary radiation. Physics Review

50. To compensate for the reduced radiation for coned down views, the mAs is increased. 14 x 17 to 8 x 10 times 1.4 14 x 17 to 10 x 12 times 1.25 The technical factors are a balancing act. We balance patient exposure and contrast. We use the highest kVp that will provide adequate contrast. Physics Review