X-Ray Interaction With Matter Flashcards
summary of beams leaving xray unit
focused stream of photons going in the same direction
lower energy non diagnostic removed via filtration
travel in straight line at speed of light until react with something
3 types of photon interactions
transmission -
passes through unchanged
absorption -
energy fully deposited, photon ceases to exist
attenuation
scatter -
changes direction
how attenuation appears on xray image
minimal = black
partial = grey
complete = white
photoelectric effect
complete absorption, interaction with inner shell electron, absorption of photon and creation of photoelectron
[and visible light]
when energy of photon is equal or greater than binding electron
inner shell electron is ejected
prevents photons reaching receptor to lighter image
what metals are good at attenuating xray bea, and why
gold, lead
high atomic number
high photoelectric effect
therefore used for shielding
compton effect
partial absorption and scatter
photon interacts with outer shell electron, partial absorption and scatter of photon and recoil electron
when photon energy much greater
loss of photon energy
recoil electron can ionise and damage tissues
deflection of photons depending on energy
high energy = forward scatter
low energy = back scatter
70kV = forward scatter,
- why controlled area needs to surround pt as not safe
direction of scatter and their effect on the image
back, sideway = do not reach receptor, no effect
slightly obliquely forward = darkening of image in wrong place, fogging, reduces quality
reducing scatter via collimation positive effects
lower surface area irradiated
lower volume of irradiated tissue
lower number of scattered photons produced in tissue/interacting with receptor
lower loss of contrast on image
reduces pt dose and radiation
photoelectric and compton effect impact on radiation dose
photoelectric -
increases pt dose, but necessary for photo formation
compton -
increased pt dose but scattered photons do not contribute to image, may increase dose to operators via back scatter
effect of lower kV on xray unit
lower energy photons
increased photoelectric
increased contrast between tissues
increased dose by pt
effect of increasing kV on xray unit
higher energy photons
lower photoelectric effect
increased forward scatter
lower pt dose
decreased contrast between tissues
continuous /characteristic radiation interaction summary
occur in xray tube [target]
electrons interact with tungsten atoms
lead to production of xray photons
photoelectric /compton effect summary
occur in pt/receptor/shielding
photons interact with atoms
lead to attenuation of xray beam
