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RAD 254 Chapter 15 Radiographic Technique

RAD 254 Chapter 15 Radiographic Technique. 4 primary exposure factors are: kVp, mA, time, distance. In the next 10 minutes:. Write down “bullets” about what happens when one raises kVp. Memory jerk for grids. Write the following: 5 2 8 4 12 5 16 6. Now what???. kVp.

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RAD 254 Chapter 15 Radiographic Technique

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  1. RAD 254 Chapter 15Radiographic Technique 4 primary exposure factors are: kVp, mA, time, distance

  2. In the next 10 minutes: • Write down “bullets” about what happens when one raises kVp

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

  4. 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)

  9. 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)

  10. 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 = <1% ripple

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