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:

Now what???

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

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

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 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)

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)

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