X-ray Tube

Question 1

what are the parts of a dental X-ray tube

Answer 1

Control Panel
Extension Arm
Tubehead
PID (the tube)
BAsic parts: tube head and control pannel

Question 2

what does PID stand for

Answer 2

position indicating device

Question 3

what does the tube head contain

Answer 3

X ray tube and Position indicating device

Question 4

how is the tubehead suspended

Answer 4

from a flexible extension arm

Question 5

why is the extension arm hollow

Answer 5

enables wires to pass through

Question 6

what is found on the control panel of a dental radiographic machine

Answer 6

On/off switch
exposure botton with indicator light and audible signal
expose time, KvP and mA selection

Question 7

where is the control panel mounded

Answer 7

Wall or portable control box

Question 8

what does the control panel do

Answer 8

turs on machine and adjusts settings (Kilovolts, Milliampers, exposure time)

Question 9

what does federal laq require the exposure button be connected to

Answer 9

Indicator light and audible signal

Question 10

what happens when the exposure button is depressed

Answer 10

Indicator light and sound is activited

Question 11

what type of switch is the exposure button

Answer 11

Dead man type(switch works only with continuous pressure)

Question 12

how long do you hold the exposure button down

Answer 12

Until the sound is over and the light is off

Question 13

what are the 4 conditions for the production of X-rays

Answer 13

• Separation of electrons from tungsten filament at cathode
• production of high speed electrons to ensure enought KE needed for the production of X-rays
• focusing of electrons on a small region on the anode
• sudden stopage of electrons creating x-ray photons

Question 14

why do electrons repel each other

Answer 14

negative charge

Question 15

where are electrons focuesed

Answer 15

On the focal spot of the anode

Question 16

what does the anode do to the electrons

Answer 16

stops and slows electrons

Question 17

what types of interactions form when an electron slows

Answer 17

Bremsstrahlung

Characteristic

Question 18

how are electrons originally separated

Answer 18

By the formation of an electron cloud by heating of tungsten filament at low voltage

Question 19

is the anode or cathode the source of electrons

Answer 19

Cathode

Question 20

what is the cathode made of

Answer 20

tungsten

Question 21

what voltage is used to heat the cathode

Answer 21

6-12 volts

Question 22

what is the process of using heat to produce electrons

Answer 22

Thermionic emission

Question 23

what provides the necessary current to the tungsten filament

Answer 23

Step down transform

Question 24

why is tungsten used in the cathode

Answer 24

High Z number

Question 25

what is the voltage difference between cathode and anode

Answer 25

1000 times higher than 110 volt wall outlet | 65000-90000 volts

Question 26

what provides the necssary voltage between the cathode and anode

Answer 26

step up transformed

Question 27

how fast are electrons accelerated

Answer 27

.5 times the speed of light

Question 28

what doe the High Voltage difference do to the electrons

Answer 28

Lead to high Kinetic energy and high speed

Question 29

what is used to focus the electons

Answer 29

A Molybdenum focusing cup at the cathode

Question 30

what is the target made of for the electron beam

Answer 30

Tungsten(anode) | copper stem

Question 31

why is tungsten used as the Anode

Answer 31

High Atomic number High melting point Low VP

Question 32

efficiency of X-ray production

Answer 32

99% of electron energy transformed as heat, 1% converted to X-rays

Question 33

why is the tungsten target embeeded in a copper stem

Answer 33

Need a good thermal conductor to dissipate heat

Question 34

what fills the X-ray tube

Answer 34

Nothing, it is a vaccume

Question 35

why does a metal housing surround the glass X-ray tube

Answer 35

Protect tube from accidental damage | prevents overheating by giving a potential space to fill with oil

Question 36

what determines the current of the X-ray tube

Answer 36

By the Low voltage side

Question 37

High current X-ray tubes do what to Xrays

Answer 37

create lots of X-rays

Question 38

High voltage difference does what X-rays

Answer 38

X-rays are higher energy

Question 39

problem with placing metal in a vaccum

Answer 39

Metal must not vaporize(good cuz tungsten has low vapor pressure)

Question 40

How "pure" is the beam of X-rays leaving the tube

Answer 40

Different wavelengths with Different enegy

Question 41

what does filtration of X-rays do

Answer 41

preferentially removes low energy X-ray photons from beam, reducing dose to patient

Question 42

what is inherent filtration

Answer 42

The glass covering and oil in the tube that stops low energy X-rays

Question 43

What is total filtration

Answer 43

Aluminum and inherent Filtration

Question 44

what is the Aluminum equivalent

Answer 44

The thickness of aluminum (in mm) which gives the same filtration as the inherent filtering material (glass and oil) of x-ray tubehead under same conditions

Question 45

how much total filtration must be used if 50-70KVp

Answer 45

1.5mm total (inherent +AI)

Question 46

How much total filtration must be used above 70KVp

Answer 46

2.5mm total(inherent +Al)

Question 47

why is the tube placed in oil

Answer 47

Insulationa nad heat

Question 48

What does filtration do to exposure time and skin dose

Answer 48

INcreases exposure time up to 50% to account for loss inintensity reduces patient skin exposure as much as 80%

Question 49

what do you do if you use an Xray machine below 60KVP

Answer 49

don't use it, need to overexpose patient to produce an acceptable radiograph

Question 50

what are the facotrs that control the X-ray beam

Answer 50

``` Tube Voltage Exposure time Tube current Filtration Collimation Distance ```

Question 51

what does A high amount of voltage do number and energy of photons

Answer 51

More photons(higher quantity( and higher energy(higher quality)

Question 52

what does KVp control in an electron

Answer 52

Control the speed (KE) of each electron) leading to higher energy photons and X-rays

Question 53

what is the Rule of Thumb for KVP

Answer 53

an increase in 15% in KvP should be followed by a reduction in 1/2 mAs

Question 54

what happens to the expsore timeif you increase by 15kVP to get the same density

Answer 54

1/2 exposure time

Question 55

what happens to the exposure time if you decrease by 15kVP to get the same density

Answer 55

double exposure time

Question 56

why does low KVP lead to less dense images

Answer 56

longer wavelengths and lower energy so less penetration

Question 57

what does Increaseing exposure time do

Answer 57

INCresaes the amount of x rays produced

Question 58

what does an increase in current ddo to the x-rays

Answer 58

Increases the quantiy of x-rays produced

Question 59

what one factor determines the total number of x-ray photons produced in the beam

Answer 59

miliamp seconds

Question 60

what should remain constant for a particular exposure

Answer 60

miliamp seconds(increase time, decrease miliamps

Question 61

what does Collimation do

Answer 61

Minimizes the amount of radiation to patients and reduces scatter, protecteing patient from unnecessary radition

Question 62

what is the most effective beam limiting device

Answer 62

Collimator

Question 63

do all X-ray tubes have collimators

Answer 63

Yes, made of lead

Question 64

what does Federal law require that a collimator should restrict a beam to

Answer 64

no more than 7cm(2.75 inches) at the skin surface of the patient when making an intraoral dental radiograph

Question 65

what is the relationship between intesnity of radiation and distance

Answer 65

Inverse square(intensity decreases inversly as the square of the source film distance)