1electromagnetic radiation
movt of energy as combination of electric and magnetic fields, like XRAY!
no mass/weight, charge
travels at speed of light
2xray tube components
cathode, anode, glass envelope, power supply
3cathode is what charged
negatively charged
4cathode made of
tungsten wire filament
5when current applied to cathode
heats up, relases electrons (thermionic emission)
6what is space charge
when the released electrons from the cathode create a cloud of elec around the filament
7why is the cathode made out of tungsten
high melting point, need to withstand 99% of e- being lost as heat
8anode charged
positively to attract electrons
9focal spot bevel
bevel 20deg to absorb large amt e- and dissipate heat
10line focus principle
if focal spot large, dissipate heat well but image not sharp. if FS too small cant dissipate heat
thus line focus prin: small APPARENT focal spot for sharpness, actual focal spot large for heat
that is done through bevel
11metal tubehousing
thick metal sealing xray components, absorb most of scatter radiation
12what absorbs the leftover electrons/photons emitted
aluminum filter
13tube current
flow of e- through tube from cath to an
14tube voltage
high volt req'd bt cath and an to generate xray
15what causes unnecessary exposure to patient
low energy photons that cannot reach image receptor
16how to reduce unnecessary exposure to pt
metallic disk or filter
filters: aluminum or tube housing+oil+glass
17collimators
devices used to regulate shape and size of beam
18requirements for collimation size
circle of 2.75in or 7cm diameter
19types of interactions producing radiation in tungsten**
bremsstrahlung or braking
characteristic radiation
20bremsstrahlung
most xrays
high energy e- interacting with nucleus, which loses kinetic energy that is emitted as radiation
21characteristic radiation
when inner orbit e- removed from high E e-'s, vacancy in atom, turning pos charge
atom returns to neutral by emitting excess energy as radiation
22xray energy spectrum for both radiation types
bremsstrahlung: continuous spectrum
(60-70 kbp for dentistry)
characteristic: discrete
23factors controlling xray beam
exposure time (impulses; mAs = quantity of xrays produced)
tube current (mA)
tube voltage (kVp = quality of xrays produced)
24effect of exposure time has direct effect on
quantity of photons
25when exposure time is doubled (constant kvP and mA)**
number of photons generated at all E doubled
mean and maximal energy remain same
26effect of tube current has direct effect on
number of e- produced
27as mA is increased
more power to filament, more e- produced and collide w anode
28effect of kVp; inc?
both quality and quantity
inc > inc amt radiation produced, inc mean energy of xray
29inverse sq law
intensity of xray beam decreases by power of 4 because the area of xray spreads out