elastic interaction
photon looses no energy
inelastic interaction
transfer of energy from photon into matter
absorption
photon looses all energy and disappears
classical scattering
interacts with whole atom
no ionisation
elastic interaction
infrequent
looses some energy at wrong angle = noise
photoelectric
interaction between photon and inner shell
complete absorption of photon energy by electron so electron gets booted.
(ionisation must be stronger then binding energy)
will produce free radicals
compton scattering
interaction between photon and outer shell electrons
inelastic
electron gets ejected(ionisation)
photon continues on at different angle with lower energy
quantom motle
noise
ambient radiation
photon hitting the object but then diverging onto a different path
if image is noisy
up mAs
angular distribution
scattering angle changes with kv
as kv increases photons become more foward scattered
attenuation
amount of photons removed from the primary beam by scatter or absorption
depends on
density
thickness
energy of beam
cross section
apparent area a photon can interact with
linear attentuation co efficient
fractional number of photons that are removed(attentuated) per cm of that tissue
inherint contrast
different l.a.c between tissues with the interactions with the energy we choose
half value layer
the thickness of the material required to reduce the intensity of the beam by half
homogenous beams
consist of 1 energy photon
heterogenous beams
multiple photon energies
as photons travel further through the medium
the quality of the beam increases
beam hardening
as lower energies go away the beam becomes higher energy and the average increases
filter(ation)
pre hardens beam and gives better image and reduces dose
can be aluminium
