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Principles of X-ray Production (Properties of X-ray (Can cause biological…
Principles of X-ray Production
Properties of X-ray
Travel in a straight line
Travel at the speed of light
Have no charge/ mass
Are invisible
Cannot be felt
Cannot be deflected by magnetic fields
Can ionise atoms
Can cause fluorescence
Can cause biological damage
Direct
Interact with biological DNA
Indirect
Interact with water molecules and cause formation of free radicals
Polychromatic beam
Classification of biologic effects
Stochastic effects
No known lower threshold
Severity of effect independent of dose
Examples: Cataracts, haematopoetic damage
Deterministic effects
Damage only over a threshold dose
Radiation protection
ALARA
Dose monitoring in personnel
Dosimeter worn under protective clothing
Dose limiting
Collimation
Reduce area of exposure to area of interest
Reduce scatter radiation
Shielding
Only protects against scatter radiation
Distance
Inverse square Law
Controlled and regulated areas of ionising radiation
Filtration
Reduce dose to patient
Units
Exposure
Coulumb/kg
Roentgen
Absorbed Dose
Sievert (Sv)
Effective Dose
Gray
mAs
number of electrons
kvP
penetration power
acceleration of electrons
High kV technique ideal for thorax
Number of electrons
Production of X-rays
Anode
Positively charged target
Tungsten
High atomic number
High conversion efficiency from electrons to x-rays
Relatively resistant to surface damage
HIgh melting point
Rotating anode and positioned at a slanted angle
Cathode
Negatively charged filament
Small filament
Smaller focal spot
Greater detail
Concentrates heat
Larger filament
Reduced detail
Can use higher exposure
Larger effective focal spot
Effective focal spot
Control panel
Interaction of X-rays with matter
Attenuation
Decrease in intensity of X-ray as it passes through matter
Crompton Effect
Depends on density
Photon ejects outer shell electron
Scattered photon
Fogs film
Safety hazard
Photoelectric Effect
Depends on cubed atomic number
Complete absorption of X-ray photon
Ionisation and ejection of photoelectron
Electron from higher shell falls into space
Radiation given off
Transmission