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RAD 354 Chap. 13 Radiographic TechniquePowerPoint Presentation

RAD 354 Chap. 13 Radiographic Technique

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RAD 354 Chap. 13 Radiographic Technique

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- Four PRIMARY exposure factors:
- kVp
- mA
- Time
- distance

- Write down “bullets” about what happens when on RAISES kVp

- Write the following:
- 52
- 84
- 125
- 166

- 5:1 = 2X mAs
- 8:1 = 4 X mAs
- 12:1 = 5 X mAs
- 16:1 = 6 X mAs

- 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

- 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

- 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)

- 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

- 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)

- 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