XRAY PHYSICS

Question 1

Roentgen/ Air kerma

Answer 1

quantity of exposure (Roentgen kerma think bad karma on russian spy so theyre gonna be exposued to a high amount of xray)

Question 2

Rad/ Gray

Answer 2

Quantity of exposed xray that is actually absorbed

10-20Gy is lethan to us

Question 3

Rem (r)/ Sievert (Sv)

Answer 3

the effective biological damage that the abs radiation has caused (not all xrays are equally lethal) 2 Sv is lethal dose to humans

Question 4

Curie/ Becquerel

Answer 4

quantity of radioactivity

Question 5

exposure

Answer 5

amount of ionization that is produced when radiation passes through the body

Question 6

Absorbed dose

Answer 6

amount of ENERGY abs by body when radiation passes through it

Question 7

Dose equivalent

Answer 7

bio damage caused by radiation

Question 8

Effective dose equivalent

Answer 8

measures biodamage to a specific organ

Question 9

how much does.. rad=gY=cGy=mGy?

Answer 9

1 rad= .01 Gy=1cGy=10mGy

Question 10

how much does rem=Sv=cSv=mSv?

Answer 10

1rem=.01Sv=1cSv=10mSv

Question 11

Attenuation

Answer 11

the idea that some tissue abs more xrays than other tissues which leads to diff shades of gray on film

Question 12

radiopaque

Answer 12

tissues that ABS xrays and appear white

Question 13

Radiolucent

Answer 13

tissue that allows for complete penetration of xray and will appear black

Question 14

Inverse square law

Answer 14

“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

Question 15

kVp

Answer 15

• energy of the xray beam
• normal: 50-70 kVps
• manpulates energy/QUALITY of xray and a little bit of quantity too

Question 16

mA

Answer 16

• controls NUBMER of photons produced
• normal: 10-30mAs
• affects quantity/AMOUNT of xray

Question 17

Timer

Answer 17

• controls length of exposure
• normal: 1/60-1/100 of a second
• manipulate quantity (amount) of xray

Question 18

what is the minimal Source to Image distance? (SID)

Answer 18

12 in from patient

-alters number of photons stirking the film

Question 19

cathode

Answer 19

• negative electrode of xray tube
• has:
  - Filament (makes electrons when heated (mA))
  - focusing cup (directs filament electrons to the anode)

Question 20

Anode

Answer 20

• 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

Question 21

Filtration

Answer 21

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

Question 22

Characteristic radiation

Answer 22

• 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

Question 23

Bremsstrahlung radiation

Answer 23

• 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

Question 24

what happens when you increase mA?

Answer 24

-inc QUANTITY only

Question 25

What happens when you increase kVP?

Answer 25

-mainly increases quality and little bit of quantity

Question 26

how does filtration affect xray quantity/ quality?

Answer 26

- dec quantity | - inc quality

Question 27

Line focus principle

Answer 27

-allows a large area for heating while maintaining a small focal spot size (stationary anode)

Question 28

actual focal spot vs effective

Answer 28

- 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

Question 29

Heel effect

Answer 29

-xray beam has a greater intensity at cathode side and thus you must position thicker portion of body closer to cathode

Question 30

which process produces xrays?

Answer 30

Bremsstralung radiation

Question 31

Coherent scattering

Answer 31

-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

Question 32

Compton scattering

Answer 32

- 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)

Question 33

photoelectric effect

Answer 33

- 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

Question 34

finish this statement... "diagnostic image is formed by the ? and ?"

Answer 34

photoelectric effect and remnant radiation

Question 35

finish this statement "most xrays interact w/ matter via ? scattering which casues image?"

Answer 35

compton, fog

Question 36

how does low kVP affect image (not quality)?

Answer 36

favors photoelectric effect, increases dose of radiation and more radiation is abs by the body

Question 37

How does high kVP affect image (not quality) ?

Answer 37

- favors Cmopton scattering | - more ratiation makes its way to the xray film because less is abs by bodY)

Question 38

Opical density

Answer 38

-amount of darkening in a radiograph | -

Question 39

mAs

Answer 39

-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

Question 40

law of reciprocity

Answer 40

-as mAs increase, xray quantity and radiograph density increases proportionally

Question 41

radiographic contrast

Answer 41

-difference in densities that allows for distinction between 2 adjacent densities in the same image

Question 42

Subject contrast

Answer 42

- result of attenuation difference as xrays pass through body - affected by tissue thickness

Question 43

short contrast

Answer 43

- used in food/ankle images - high contrast images that distinguishes bone from soft tissues - has few shades of gray

Question 44

long contrast

Answer 44

- used in abdomen - diff between soft tissues - low contrast image and thus has higher shades of gray

Question 45

what is the primary factor in controlling contrast?

Answer 45

- kVp | - high kVP -> low contrast

Question 46

how do you produce short contrast?

Answer 46

-increase mAs by 2x AND dec kVP by 15%

Question 47

how to you produce lengthened contrast?

Answer 47

dec mAs by 1/2 and increase kVP by 15%

Question 48

relationship between focal spot size and detail?

Answer 48

larger focal spot size --> decreased detail

Question 49

relationship between OID

Answer 49

-the greater the distance -> less detail/sharpness

Question 50

SID relationship

Answer 50

-greater the distance the sharper the image (but need to increase mAs too)

Question 51

how can you increase image definition/ spatial resolution?

Answer 51

- small focal spot size - decreased OID - increased SID - slow film speed

Question 52

how does shape distortion happen?

Answer 52

- 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