Other Factors that Impact Detail

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

2. 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.

3. 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.

4. 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.

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

6. 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.

7. 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.

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

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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

16. 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.

17. 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.

18. 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.

19. 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.

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 15% Rule or The Rule of 10 • If the kVp is increased by 15%, the mAs is reduced 50%. Less Contrast but shorter exposure time • If the kVp is decreased by 15%, the mAs is doubled. More Contrast but longer exposure time. • Between 60 & 90 kVp , 15% = 10 kVp

27. mAs Rule of Reciprocity • mAs = mA times the exposure time. • Any combination of mA and exposure time that produces the same mAs should produce the same level of density on the film. • mAs must be changed by 20 to 30% to make any change in density on the film.

28. mAs 50% Rule • 50% change needed to make significant change sometime referred to as the 50% rule. • Under exposed: Double mAs • Over exposed: Reduce mAs 50%

29. The End Return to Lecture Home Page