Introduction Flashcards
ionization
electron is removed –> ion pair
ionizing radiation sources
cosmic, radon, imaging
radon gas
largest source of natural radiation
x-ray discovery
- 11/9/95, Wilhelm Roentgen
x-ray properties
- penetrability
- ionizating
- fluoresce and emit light
imaging system components
- tube
- operating console
- high-V generator
x-rays are emitted..
isotropically (all directions)
cathode
- negative end
- thoriated tungsten –> heat resistant filament
thermionic emission
filament temp rises until outer shell electrons “boil off”
focusing cup
(-) charged and confines accelerated electrons toward anode
anode
- (+)
- target (conductor)
- dissipates heat
rotating anodes
reduced heat damage to tube
disadvantage of line-focus principle
anode heel-effect: electrons interact with target at various depths
uniform tissue exposure
anode must face thinner body part
Will the grid reduce extrafocal radiation?
NO
x-ray (high voltage) generator
modifies incomig voltage and current
control panel
technical factors (mA, kV, Time)
transformer
modifies voltage
step-up transformer
V increase and I decreases for greater beam energy
step-down transformer
V decrease and I increase to heat cathode for thermionic emission
rectifiers
AC –> DC
high-frequency power generator
provides constant potential V waveform which doubles radiation
collimator
restricts x-ray to target area
added filtration
aluminum filters to harden beam and improve penetrability and lessen scatter radiation
bucky system
grid that removes scatter radiation
Radiographic film
polyester and coated with emulsion containing silver halide crystals (SHC)
mAs
- milliamperage per second
- mAs –> x-ray quantity
kVp
- kilovoltage peak
- kVP –> x-ray quality (penetrability)
4 % kVp change
visible film changes
change of 5-10 kVp = …
50% change in mAs
change in visible optical density
30 % change in mAs
10 kVp rule
change kVp by 10 results in same image density change as by increasing/decreasing mAs by 50 %
penumbra
- ” almost, nearly”
- blurring of image
- increasing object film distance will increase penumbra
radiation intensity
inversely related to the square of the distance from the source
