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 Cassettes or
  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
Physics Review

• 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

21
Physics Review

• 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.

22
Physics Review

• 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.

23
Physics Review

• 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.

24
Physics Review

• 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.

25
Physics Review

• 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.

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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

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The End

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