RAD 254 Chapter 15 Radiographic Technique

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RAD 254 Chapter 15Radiographic Technique

• 4 primary exposure factors are
• kVp, mA, time, distance

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In the next 10 minutes

• Write down bullets about what happens when one
  raises kVp

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Memory jerk for grids

• Write the following
• 5 2
• 8 4
• 12 5
• 16 6

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Now what???
5
kVp

• Beam quality
• Primarily responsible for quality, BUT increases
  in kVp also make x-ray production slightly more
  productive
• Penetrability
• Beam intensity
• HVL
• Biggest exposure factor affecting CONTRAST

6
mA

• Directly responsible for amount of radiation
  produced (Quantity) As mA is doubled, so is the
  number of photons produced and so is PATIENT DOSE
• mA stations also are responsible for focal spot
  size selection

7
Time

• Exposure times should be practical and short
  enough to stop patient motion but the shortest
  times also result in the most radiation output
  per unit of time thus more wear and tear on the
  x-ray tube
• mAs time X mA
• mAs is only measured by tube current
• Responsible for Optical Density (OD)

8
Distance (SID)

• The most forgotten exposure factor but perhaps
  the most important
• Inverse square law
• Primarily affects Optical Density (OD)
• No affect on quality
• Other distance related terms
• FFD, FOD, OFD, FRD, ORD, SSD
• Other geometric factors (focal spot size, patient
  size, part orientation to CR and film)

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Filtration

• Inherent (.5 mm al equiv)
• Added (2.0 which may also include some filtration
  from localizer light apparatus, etc)
• Total filtration inherent added (2.5 mm al
  equivalent)

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Generators

• Half wave (120 cycles/sec 60 impulses per
  second) 100 ripple
• self rectified is also a half wave unit where
  the X-RAY TUBE is the rectifier (no diodes)
• Full wave rectification (120 cycles per second
  120 impulses per second) 100 ripple
• 3 phase, 6 pulse 14 ripple (33 more radiation
  produced per exposure over full wave)
• 3 phase, 12 pulse 4 ripple (40 more
  radiation produced per exposure over full wave)
• Hi frequency lt1 ripple