Radiology - X-Ray Unit

Front 1

the ability of xray photons to penetrate matter is dependent on

Back 1

their energy

Front 2

the energy level of x-ray photons determines

Back 2

the amount of penetration that you get rather than absorption

Front 3

how are x-ray photons released

Back 3

- a tungsten filament is heated until it releases electrons in a cloud
- electrons are acclerated through an electromagnetic field
- they collide with a tungsten target, transferring their energy and releasing it as an x-ray photon

Front 4

x-rays are generated out of

Back 4

k, l, m orbitals

Front 5

components of a x-ray head

Back 5

- tube
- power source
- collimator
- aiming cylinder
- oil
- aluminum filter

Front 6

why is the head filled with oil

Back 6

to dissipate heat

Front 7

standard for aluminum filtration

Back 7

1.5 mm to 70 kVp (2.5 above 70 kVp)

Front 8

what does the collimator do

Back 8

narrows the x-ray beam

Front 9

aiming cylinder also known as the

Back 9

cone

Front 10

what does aiming cylinder do

Back 10

also narrows the beam

Front 11

why do we use tungsten

Back 11

- large atom with a lot of electrons (high atomic number)
- high thermal conductivity
- high melting point
- low vapor pressure

Front 12

what does the focusing cup do

Back 12

localizes electrons

Front 13

electrons are sped up by the

Back 13

kVp setting

Front 14

kVp setting determines the

Back 14

energy level of electrons

Front 15

quality setting

Back 15

kV

Front 16

quantity setting

Back 16

milliampage and exposure time

Front 17

focal spot

Back 17

the focal spot is the area on the tungsten target to which the focusing cup directs the electrons from the filament

Front 18

the sharpness of the radiographic image __________ as the size of the focal spot __________

Back 18

increases; decreases

Front 19

effective focal spot

Back 19

the projection of the actual focal spot, perpendicular to the electron beam

Front 20

actual focal spot size

Back 20

1 mm x 3 mm

Front 21

effective focal spot size

Back 21

1 mm x 1 mm

Front 22

why is angulation of the target importent

Back 22

it decreases the size of the effective focal spot, which increases sharpness

Front 23

typical angulation of target

Back 23

20 degrees

Front 24

as the angulation of the target increases

Back 24

the focal spot increases

Front 25

how does emulsion effect sharpness

Back 25

emulsion on both sides decreases sharpness

Front 26

bremsstrahlung radiation is produced by

Back 26

- direct hit of electron on nucleus in the target
- or by the passage electrons near the nucleus, which results in the electrons being deflected and decelerated

Front 27

maximum energy of a photon is generated when

Back 27

a high energy electron directly hits the nucleus and transfers energy

Front 28

when you double exposure time ______________________________

Back 28

you double the relative number of photons generated

Front 29

what happens to the mean energy level of the electron beam as you double exposure time

Back 29

it remains the same

Front 30

characteristic radiation

Back 30

occurs when an electron from the filament displaces an electron from a shell of a tungsten target atom

Front 31

what happens if you double the mA setting

Back 31

you double the amount of photons generated

Front 32

what happens when you increase kVp

Back 32

1- increase number of photons
2- increase mean energy level
3- increase maximal energy

Front 33

high energy photons have a higher probability of __________________

Back 33

penetrating matter

Front 34

low energy photons have a higher probability of ____________________

Back 34

being absorbed

Front 35

how do you double darkness? what if its too dark?

Back 35

change the kVp setting by 15; decrease the time

Front 36

how collimation of an x-ray beam acheived

Back 36

by restricting its useful size

Front 37

name different types of collimators

Back 37

round collimators
rectangular collimator

Front 38

target-to-film distance in short cones

Back 38

8 inches

Front 39

target-to-film distance in long cones

Back 39

16 inches

Front 40

which has a narrower electron beam: long or short cone?

Back 40

long cone

Front 41

compton absorption

Back 41

occurs when an incident photon interacts with an outer electron, producing a scattered photon of lower energy than the incident photon and a recoil electron ejected from the target atom

Front 42

compton absorption makes up what percentage of the interactions of photons

Back 42

49%

Front 43

coherent scattering

Back 43

low-energy incident photon interacts with an outer electron, causing electron to vibrate momentarily. a scattered photon of the same energy level is emitted at a different angle

Front 44

coherent scattering makes up what percentage of photon interactions

Back 44

7%

Front 45

photo-electric absorption

Back 45

an incident photon gives up all its energy to an inner electron, which is ejected from the atom (photo-electron)

Front 46

photo-electric absorption makes up what percentage of photon interactions

Back 46

23%

Front 47

exposure = ?

Back 47

the measure of radiation quantity to ionize air

Front 48

what is the SI unit for exposure

Back 48

KERMA (kinetic energy released in matter)

Front 49

KERMA =

Back 49

joules/kg

Front 50

absorbed dose (Dt)

Back 50

measure of the energy absorbed by unit mass by any type of matter

Front 51

unit of absorbed dose (Dt)

Back 51

grey (used to be rads)

Front 52

1 grey = ?

Back 52

100 rads

Front 53

equivalent dose (Ht)

Back 53

compares the biological effects of different types of radiation on an organ or tissue

Front 54

unit of measure of equivalent dose

Back 54

sievert

Front 55

Wr for photons =

Back 55

1

Front 56

Wr for 5 keV neutrons =

Back 56

5

Front 57

Wr for alpha particles =

Back 57

20

Front 58

how do you find Ht

Back 58

the sum of all Wr multiplied by Dt

Front 59

effective dose (E)

Back 59

estimates risk of radiation in humans or whole body

Front 60

Wt for breast, colon, lung, stomach, red bone marrow

Back 60

.12

Front 61

Wt for gonads

Back 61

.2

Front 62

Wt for bladder, esophagus, liver, thyroid

Back 62

.04

Front 63

Wt for bone surface, skin, salivary glands, brain

Back 63

.01

Front 64

how is E calculated

Back 64

sum of Wt multiplied by equivalent dose

Front 65

radioactivity

Back 65

describes the decay rate of radioactive materials

Front 66

SI unit of radioactivity

Back 66

bacquerel (Bq)

Front 67

key interproximal space for PA's

Back 67

between 1st molar and 2nd premolar - it should be open

Front 68

attenuation

Back 68

the reduction of intensity of a photon beam as it passes through matter, resulting through interactions of individual photons with atoms of the absorber

Front 69

main means of attenuation of a photon beam

Back 69

- coherent scattering
- photoelectric absorption
- compton absorption
- 9% of photons pass through the head without interaction

Front 70

which form of attenuation is most important for high quality radiographs

Back 70

photoelectric absorption