XRAY PHYSICS Flashcards
Roentgen/ Air kerma
quantity of exposure (Roentgen kerma think bad karma on russian spy so theyre gonna be exposued to a high amount of xray)
Rad/ Gray
Quantity of exposed xray that is actually absorbed
10-20Gy is lethan to us
Rem (r)/ Sievert (Sv)
the effective biological damage that the abs radiation has caused (not all xrays are equally lethal) 2 Sv is lethal dose to humans
Curie/ Becquerel
quantity of radioactivity
exposure
amount of ionization that is produced when radiation passes through the body
Absorbed dose
amount of ENERGY abs by body when radiation passes through it
Dose equivalent
bio damage caused by radiation
Effective dose equivalent
measures biodamage to a specific organ
how much does.. rad=gY=cGy=mGy?
1 rad= .01 Gy=1cGy=10mGy
how much does rem=Sv=cSv=mSv?
1rem=.01Sv=1cSv=10mSv
Attenuation
the idea that some tissue abs more xrays than other tissues which leads to diff shades of gray on film
radiopaque
tissues that ABS xrays and appear white
Radiolucent
tissue that allows for complete penetration of xray and will appear black
Inverse square law
“the farther away youre from an energy source the less youll be exposed to it”, light intensity from a source is inversely proportional to the square distance between the object and the source
kVp
- energy of the xray beam
- normal: 50-70 kVps
- manpulates energy/QUALITY of xray and a little bit of quantity too
mA
- controls NUBMER of photons produced
- normal: 10-30mAs
- affects quantity/AMOUNT of xray
Timer
- controls length of exposure
- normal: 1/60-1/100 of a second
- manipulate quantity (amount) of xray
what is the minimal Source to Image distance? (SID)
12 in from patient
-alters number of photons stirking the film
cathode
- negative electrode of xray tube
- has:
- Filament (makes electrons when heated (mA))
- focusing cup (directs filament electrons to the anode)
Anode
- positive electrode
- Target: e- produced by cathode are directed and made of tungsten and make xrays
- focal spot: area on target from which xrays are emitted
Filtration
you add filtration so that beam comes out and is abs and wont reach the xxray plane
- inherent:abs off focus radtion that doesnt contrbute to producing a good image
- added: filters the useful xray beam and abs low energy xrays that cant reach the image
Characteristic radiation
- e interacts w/ atom’s inner shell e and removes the e which causes ionization
- xray photons produced as outer shell e fill inner shells
Bremsstrahlung radiation
- E slows down/ brakes as it passes by post charged nucleus
- changes course of E which causes it to lose E in the form of xray photons
what happens when you increase mA?
-inc QUANTITY only
What happens when you increase kVP?
-mainly increases quality and little bit of quantity
how does filtration affect xray quantity/ quality?
- dec quantity
- inc quality
Line focus principle
-allows a large area for heating while maintaining a small focal spot size (stationary anode)
actual focal spot vs effective
- actual: location on tungsten target where e- are directed FROM the cathode and is tilted so that the xrays strike a larger area which spreads out heat (increase of incident beam increases actual foca spot)
- effective: seen by the image receptor, is smaller than actual focal spot
Heel effect
-xray beam has a greater intensity at cathode side and thus you must position thicker portion of body closer to cathode
which process produces xrays?
Bremsstralung radiation
Coherent scattering
-as xray photons excite target atom a secondary photon of equal energy is released in diff direction and will be abs by patient and will not contribute to the image
Compton scattering
- when xray photo interact with matter and egects an OUTER shell e- -> ionization
- causes xray to continue in diff direction with dec E
- creates a “fog” and affects image quality (dec contrast)
photoelectric effect
- Xray photon is abs and an INNER shell e- is ejected during ionization
- causes mean attenuation and image formation
- contributes to patient’s abs dose
finish this statement… “diagnostic image is formed by the ? and ?”
photoelectric effect and remnant radiation
finish this statement “most xrays interact w/ matter via ? scattering which casues image?”
compton, fog
how does low kVP affect image (not quality)?
favors photoelectric effect, increases dose of radiation and more radiation is abs by the body
How does high kVP affect image (not quality) ?
- favors Cmopton scattering
- more ratiation makes its way to the xray film because less is abs by bodY)
Opical density
-amount of darkening in a radiograph
-
mAs
-the primary controlling factor of an image
-mAxseconds
-inc mAs -> darker image
inc mAs by factor of 2
dec mAs by factor of 1/2
law of reciprocity
-as mAs increase, xray quantity and radiograph density increases proportionally
radiographic contrast
-difference in densities that allows for distinction between 2 adjacent densities in the same image
Subject contrast
- result of attenuation difference as xrays pass through body
- affected by tissue thickness
short contrast
- used in food/ankle images
- high contrast images that distinguishes bone from soft tissues
- has few shades of gray
long contrast
- used in abdomen
- diff between soft tissues
- low contrast image and thus has higher shades of gray
what is the primary factor in controlling contrast?
- kVp
- high kVP -> low contrast
how do you produce short contrast?
-increase mAs by 2x AND dec kVP by 15%
how to you produce lengthened contrast?
dec mAs by 1/2 and increase kVP by 15%
relationship between focal spot size and detail?
larger focal spot size –> decreased detail
relationship between OID
-the greater the distance -> less detail/sharpness
SID relationship
-greater the distance the sharper the image (but need to increase mAs too)
how can you increase image definition/ spatial resolution?
- small focal spot size
- decreased OID
- increased SID
- slow film speed
how does shape distortion happen?
- central beam not perpendicular to film
- foot plane not parallel to film
- xray beam not centered over middle of foot
- seen with medial oblique foot xray
