Xray Production and Interaction

atom

composed of mutliple subatomic paricles

atomic number (Z)

number of protons

atomic mass (A)

proton and neutron mass

ion

atom is not neutrally charged; differeny amounts of protons and neutrons

isotope

same Z, different A

isobar

different Z, same A

istone

same number of neutrons

isomer

same molecule, different chemical structure

E = hf

higher energy molecules have higher frequency

particle radiation

includes alpha and beta radiation

electromagnetic radiation

• gamma rays

• xray

• microwave s

• visible light

natural sources of radiation

• radon

• terrestrial

• cosmic

• internal

• bananas

man made sources of radiation

• CT scans

• radiographs

Do MRIs give off radiation

no

radioactive decay

• as atoms gets larger, the amount of neutrons tends to exceed protons

• nucleus becomes unstable

• may spontaneously emit particle radiation

electromagnetic radation

produed when the velocity of a charged particle is altered

ionizing radiation

exist at a higher frequency than visible light

generation of xrays

• create electrons

• interact with target

• create x rays

• interact with matter

• create radiograph

cathode

• heated by power supply

• releases electrons

• negatively charged

anode

• contains tungsten target that electrons hit

• source of xray generation

• positively charged

focusing cup

• negatively charged

• helps ensure the electron beam is directed at the tungsten target

power supply

• provides high voltage for cathode and anode

• provides low voltage to heat up the cathode

current selector

• measured in mA

• indicates the number of electrons sent from cathode to anode per second

voltage selector

• measured in peak kilovoltage

• indicates maximum voltage of current

how much energy is released as heat during xray generation

99%

timer

• controls duration of exposure

• measured in seconds to impulses

rectifier

decreases variance in voltage

focal spot

smaller focal spot will give sharper images

why does anode rotate

• prevents it heating up and melting

• less time between exposure s

what is the energy of xrays measured in

electronvolts, between 0 and 70 keV

common interactions with tungsten target

• release of heat

• breaking radiation

• characteristic radiation

breaking radiation

• electron directly hits nucleus or is slowed down

• energy of photon is equal to that of incident electron or kinetic energy change

characterstic radiaton

• incident electron interacts wth and ejects an inner shell electron

• electron from outer shell takes it place

• exist in discrete units equal to difference in energy leves

common interations with patients

• no interaction

• coherent scatter

• photoelectric effect

• compton scatter

no interacion with patient

• passes thru patient

• no biological risk

• no contribution to image

• adds fog to film

coherent scatter

• low energy photon interacts with outer electron

• electron fully absorbs incident photon

• becomes momentarily excited

• returns to original energy state

• new photon is produced at a new angle

• small effect on image

photoelectric absorption

• photon hits inner electron

• inner electron ejected

• outer electron fills vacancy

• proportional to Z³/E³

• will not pass thru patient

compton scatter

• incident photon of higher energy hits outer electron

• outer electron is ejected

• E = binding energy - kinetic energy

radiolucent

• moves thru air

• lots of beams

radiopaque

• moves thru bone

• few beams get thru