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RAD 354 Chap. 13 Radiographic Technique - PowerPoint PPT Presentation

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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• 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
• 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)
• 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
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
• 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