rad 354 chap 13 radiographic technique
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RAD 354 Chap. 13 Radiographic Technique. Four PRIMARY exposure factors: kVp mA Time distance. In the next 5 minutes. Write down “bullets” about what happens when on RAISES kVp. Memory “jerk” for grids. Write the following: 5 2 8 4 12 5 16 6. Now What???. 5:1 = 2X mAs

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rad 354 chap 13 radiographic technique
RAD 354 Chap. 13 Radiographic Technique
  • Four PRIMARY exposure factors:
    • kVp
    • mA
    • Time
    • distance
in the next 5 minutes
In the next 5 minutes
  • Write down “bullets” about what happens when on RAISES kVp
memory jerk for grids
Memory “jerk” for grids
  • Write the following:
  • 5 2
  • 8 4
  • 12 5
  • 16 6
now what
Now What???
  • 5:1 = 2X mAs
  • 8:1 = 4 X mAs
  • 12:1 = 5 X mAs
  • 16:1 = 6 X mAs
slide5
kVp
  • Beam Qualtiy
    • Primarily responsible for quality, BUT INCREASES in kVp also make x-ray production SLIGHT more productive
  • Penatration
  • Beam intensity
  • HVL
  • Biggest exposure factor affecting CONTRAST
slide6
mA
  • DIRECTLY responsible for AMOUNT of radiation produced (Quantity). As mAs is doubled, so is the number of photons produced and so is PATIENT DOSE
  • mA stations are responsible for focal spot size selection
slide7
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)
distance sid
Distance (SID)
  • The most “forgotten” exposure factor, but perhaps the most important
    • Inverse Square Law
    • Primarily effects Optical Density (OD)
      • NO effect on quality
  • Other distance related terms:
    • FFD, FOD, OFD, FRD, ORD, SSD
  • Other geometric factors (F.S. size, pt. size, part orientation to CR and receptor
filtration kvp driven
FiltrationkVp driven
  • Inherent (.5 mm al equiv)
  • Added (2.0 which may also include some filtration from localizer light apparatus, etc.) in a 70-80 kVp unit
  • Total filtration : inherent + added (2.5 mm al equivalent)
generators
Generators
  • Half wave (120 cycles/sec = 60 impulses per second) – 100% ripple
    • “self rectified” is also half wave where the X-RAY TUBE is the DIODE
  • Full wave rectification (120 cycles per second = 120 impulses per second) – 1--% ripple
  • 3 phase, 6 pulse = 14% ripple (33% more radiation per exposure over full wave)
  • 3phase, 12 pulse = 4% ripple (40% more per exposure over full wave
  • Hi frequency = <1% ripple
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