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


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


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


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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