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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. 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

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  1. RAD 354 Chap. 13 Radiographic Technique • Four PRIMARY exposure factors: • kVp • mA • Time • distance

  2. In the next 5 minutes • Write down “bullets” about what happens when on RAISES kVp

  3. Memory “jerk” for grids • Write the following: • 5 2 • 8 4 • 12 5 • 16 6

  4. Now What??? • 5:1 = 2X mAs • 8:1 = 4 X mAs • 12:1 = 5 X mAs • 16:1 = 6 X mAs

  5. 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

  6. 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

  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 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

  9. 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)

  10. 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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