x-ray Flashcards
Where do x-rays originate from
tungsten target
What is the cathode
negatively charged
coil of wire - FILAMENT
What is the anode
Positively charge
TUNGSTEN TARGET - metal target into block of copper
Step- up transformer is required to ….
step up the mains voltage of 240 volts to 60-70kV
How do electrons need to travel during an x-ray exposure
electric current flows through the filament - heats it up- electrons from TT boiled off and released - cloud of electrons form around filament - travel to the target
What results in a continuous spectrum
closer the electron is to the nucleus, larger deflection therefore stronger and longer x-ray
What does the aluminium sheet do
absorbs and filters out lowest energy photons (they have lack of penetrating power)
Why is the sheet of aluminium important in radiation
to reduce radiation dose
less than 70 kV 1.5mm
kV variables
determines energy of photons
affects film contrast (lower kV shoes higher contrast)
higher kV is better - less absorption for the patient
mA and exposure variables
determine quantity of electrons and photons leaving tube
increased photons leads to increase blacking and over exposure
What does the spacer cone do
determines distance of target to patient and directs beam
Function of collimator
restricts beam size
recommended - 40mm x 50mm
The 4 interactions of x-rays with matter
absorbed
transmitted unchanged
scattered and absorbed
pure scatter (no absorption)
What effect is absorption and what effect is absorption and scatter
photoelectric
Compton
How to x-rays caused tissue damage by direct damage
photon inhibits macromolecule such as DNA or RNA
result in bond between nucleic acid breaking; point mutation
If enough damage, cells killed
If nucleic acid bonds broken - rejoin abnormally + cells divide
