Chapter Six

Question 1

list the external components of the x ray tube

Answer 1

1. support system (i.e.. floor to ceiling, ceiling, C-arm)
2. protective housing
3. enclosure (glass or metal)

Question 2

name the internal components of the x ray tube

Answer 2

1. cathode (filament and focusing cup)

2. anode (rotating, stationary)

Question 3

describe the protective housing for the x ray tube

Answer 3

lead-lined (made of metal) w/ two electrical wires that attach to the tube through a high voltage connector

Question 4

what are the roles of the protective housing

Answer 4

provides mechanical support for the time
electrical insulator
heat dissipater

Question 5

what is leakage radiation

Answer 5

anything that exits outside of the window (light field)

Question 6

true or false; there is never leakage radiation

Answer 6

False…there is ALWAYS leakage radiation

Question 7

were older or newer tube enclosures made of glass

Answer 7

older

Question 8

what material are newer tube enclosures made of

Answer 8

metal

Question 9

why was there a switch to metal enclosures from glass

Answer 9

the glass allowed gases to form and diminished the tube life due to arcing

Question 10

what is the advantage to a metal enclosure

Answer 10

maintains consistency and made for a longer tube life

Question 11

the ______ is the positive side and the _______ is the negative side

Answer 11

anode

cathode

Question 12

true or false; the cathode and the anode from a diode

Answer 12

true, they are both electrodes and together they form a diode

Question 13

what are the two primary parts the cathode

Answer 13

filament

focusing cup

Question 14

what is the filament made of

Answer 14

thorium

Question 15

why is thorium a material of choice

Answer 15

aides in thermionic emission and makes it more efficient

Question 16

what is the purpose of the focusing cup

Answer 16

makes electrons travel in a specific direction

Question 17

true or false; the focusing cup has a charge, if so what is the charge

Answer 17

true, negative charge

Question 18

what are the four things that make the focusing cup effective

Answer 18

size
shape
location
charge

Question 19

true or false; the beam is confined when using a focusing cup and decreases the consistency
explain

Answer 19

False: while the beam is confined when using a focusing cup it INCREASES the consistency

Question 20

true or false; filament current affects tube current

Answer 20

True

Question 21

low filament current = _____ tube current

Answer 21

no

Question 22

a _____ increase in filament current = a large increase in tube current

Answer 22

small

Question 23

what is the range for a low kVp

Answer 23

0-50

Question 24

in what unit is:
tube current
filament current measured in

Answer 24

tube: miliamperes (mA)
filament: amperes (A)

Question 25

true or false; there is no charge created in thermionic emission

Answer 25

false! thermionic emission creates a space charge

Question 26

list the steps of the space charge

Answer 26

electrons leave filament electron cloud surrounds filament cloud repels new electrons from filament

Question 27

describe the space charge effect

Answer 27

makes it harder to boil off new e- b/c there is no where for them to go

Question 28

what is a saturation current

Answer 28

at a given filament current a point reaches a maximum level at which all of the e- have been used

Question 29

at what point is something space charge limited

Answer 29

thermionic emission at low kVp and high mA

Question 30

how many focal spots do most diagnostic x ray tubes have

Answer 30

two one large one small

Question 31

describe the types of focal spots

Answer 31

small: better spatial resolution large: large body parts; high heat

Question 32

what are the functions of the anode

Answer 32

conducts electricity contains the target radiates heat (heat dissipator)

Question 33

how many types of anodes are there and name them

Answer 33

two; stationary and rotating

Question 34

list the materials that can be used in the anode

Answer 34

tungsten, copper, molybdenum, graphite

Question 35

in what kind of case is a stationary anode used in

Answer 35

dental

Question 36

what is the advantage of a rotating anode

Answer 36

higher heat tolerance

Question 37

what can be adde to tungsten to make it more durable and strong

Answer 37

rhenium

Question 38

where is copper used in the anode and why

Answer 38

it is used in the shaft and it conducts electricity

Question 39

what is the purpose of rotating the anode

Answer 39

so that heat diets just hit one place

Question 40

what is the RPM range for the anode

Answer 40

3,400-10,000 RPM

Question 41

what is the target

Answer 41

the area struck by the e- from the cathode

Question 42

why is tungsten a good material to be used in the anode

Answer 42

high atomic # thermal conductivity high melting point

Question 43

what materials is the inner portion of the anode made of

Answer 43

graphite and molybdenum

Question 44

describe the stator

Answer 44

electromagnets arranged to allow for electromagnetic induction and rotation

Question 45

the rotor is made of ____ and _____

Answer 45

copper and soft iron

Question 46

true or false; the rotor is outside of the glass envelope while the stator is on the inside of the glass

Answer 46

false; the STATOR is outside of the glass envelope while the ROTOR is on the inside of the glass

Question 47

how does the stator work

Answer 47

it energizes winding creating a magnetic field and inducting rotation

Question 48

what is the effective focal spot

Answer 48

the portion that the patient views

Question 49

the target can also be called ______

Answer 49

focal spot

Question 50

describe the line focus principle (LFP)

Answer 50

an angle is created on the anode to allow for detail and heat capacity

Question 51

in regard to the LFP what is done with the focal spots

Answer 51

the effective focal spot is made smaller than the actual focal spot

Question 52

what is the common anode angle

Answer 52

5-20 degrees

Question 53

true or false; the effective focal spot is controlled by the actual focal spot

Answer 53

true

Question 54

the _____ the effective focal spot the smaller the coverage area

Answer 54

smaller

Question 55

small angle _____ effective focal spot

Answer 55

small

Question 56

true or false; the intensity of the beam is altered due to the LFP

Answer 56

True

Question 57

the anode heel effect is a consequence of what

Answer 57

LFP

Question 58

describe the anode heel effect

Answer 58

x ray intensity is greater on the cathode side of the tube

Question 59

the smaller the anode angle the _____ the heel effect

Answer 59

greater

Question 60

what is off-focus radiation

Answer 60

rebounding e- causing x rays to be produced outside the focal spot

Question 61

off-focus radiation is also called what

Answer 61

extra focal radiation

Question 62

what does extra focal radiation do to image contrast

Answer 62

reduces it

Question 63

what is the most common cause of tube failure

Answer 63

excessive heat especially by using maximum techniques

Question 64

what are the three ways to dissipate heat in the x-ray tube

Answer 64

radiation conduction convection

Question 65

what is conduction

Answer 65

transfer of heat through touch; one area of material to another

Question 66

describe convection

Answer 66

liquids or gases; in the tube: oil bath that it is submerged in

Question 67

infra red is associated with what kind of heat dissipation

Answer 67

radiation

Question 68

what is the most frequent cause of abrupt tube failure

Answer 68

electron arcing from the filament to the enclosure b/c of vaporized tungsten

Question 69

name the three types of rating charts

Answer 69

radiographic rating chart anode cooling chart housing cooling chart

Question 70

what is the heat unit (HU) conversion for a single phase

Answer 70

HU= (kVp)(mA)(s) = 0.7J

Question 71

what is the heat unit (HU) conversion for a three phase

Answer 71

HU = 1.4 (kVp)(mA)(s) = 1J