Ch 6 The X-ray Tube

Question 1

the anode is the _____ end, the cathode is the ____ end

Answer 1

positive, negative

Question 2

x-rays travel from _____ to ______

Answer 2

cathode to anode

Question 3

where is heat the biggest problem?

Answer 3

at the anode

Question 4

the focal spot is the _____ source, they get there through______

Answer 4

electron, boiling off of the filament

Question 5

there are ___ filaments

Answer 5

2, a small focal spot and a big focal spot

Question 6

filaments are usually made out of:

Answer 6

thoriated tungsten

Question 7

what are the rmp rates for rotating anodes?

Answer 7

3,400 rmp & 10,000 rpm

Question 8

the _______ is on the anode side

Answer 8

induction motor

Question 9

the induction motor is made up of 2 parts:

Answer 9

rotor and stators

Question 10

the rotor:

Answer 10

rotates the anode, it is inside the glass tube proper

Question 11

the stator:

Answer 11

is made of electromagnets, provides electric and magnetic fields and electron flow, creates the force that creates the rotation, is outside of the glass tube proper

Question 12

the target is found on the _____ and is made of _____

Answer 12

anode, tungsten

Question 13

the rotor is on the ______ side and is made of _____

Answer 13

anode, tungsten

Question 14

the actual focal spot is:

Answer 14

where the electrons actually hit, where the heat is, is bigger to dissipate heat better

Question 15

the effective focal spot is:

Answer 15

what hits the IR, is smaller, provides detail

Question 16

cathode end has __% of the beam and it used on ____ parts, generally placed at the ____

Answer 16

> 100% beam, thicker parts, placed at the head end

Question 17

anode end has __% of the beam and is used on _____ parts, generally places at the ____

Answer 17

<100% beam, thin parts, placed at the feet end

Question 18

the window is:

Answer 18

made of pyrex glass, is thin, what the photons go through

Question 19

extra-focal x-rays are:

Answer 19

radiation produced anywhere else besides the anode target area of focal spot

Question 20

the primary parts of the x-ray tube are:

Answer 20

cathode (-) and anode (+)

Question 21

any electric tube with 2 electrodes is a:

Answer 21

diode

Question 22

the external structure of the x-ray includes:

Answer 22

the support structure, protective housing, and a glass or metal enclosure

Question 23

when x-rays are produced they are emitted:

Answer 23

isotropically (with equal density in all directions)

Question 24

x-rays emitted through the window are:

Answer 24

the useful beam

Question 25

leakage radiation:

Answer 25

x-rays that escape through the protective housing, they contribute nothing to diagnostics

Question 26

protective housing reduces:

Answer 26

the level of leakage radiation to less than 1 mGya/hr at 1m OR 100mR/hr at 1m from the source

Question 27

*protective housing guards against:

Answer 27

excessive radiation exposure and electric shock

Question 28

protective housing around some x-ray tubes contains oil that:

Answer 28

serves as an insulator against electric shock and as a thermal cushion to dissipate heat

Question 29

glass enclosures are made of ____ and are able to ____

Answer 29

pyrex glass, withstand tremendous heat

Question 30

the enclosure maintains:

Answer 30

a vacuum inside the tube

Question 31

the modern x-ray tube is called ____

Answer 31

Coolidge tube or vacuum tube

Question 32

metal enclosures maintain:

Answer 32

a constant electric potential b/w the electrons of the tube current and the enclosure, they have a longer life and are less likely to fail

Question 33

*x-ray tubes are designed with ___ or ___ enclosures

Answer 33

glass or metal

Question 34

the x-ray tube window is where ______, it allows____

Answer 34

the useful beam of x-rays is emitted, it allows maximum emission of x-rays with minimum absorption

Question 35

*the primary parts of the cathode are:

Answer 35

the filament and the focusing cup

Question 36

a filament is a:

Answer 36

coil of wire

Question 37

the filament emits:

Answer 37

electrons when it is heated

Question 38

when the current through the filament is high enough the:

Answer 38

outer shell electrons get boiled off and ejected from the filament, aka thermionic emission

Question 39

filaments are usually made out of:

Answer 39

thoriated tungsten

Question 40

*tungsten vaporization causes:

Answer 40

deposits on the inside of the glass enclosure, it is the most common cause of tube failure and can cause arcing

Question 41

the filament is embedded in:

Answer 41

a metal shroud called the focusing cup

Question 42

the focusing cup is ___ charged so that is:

Answer 42

negatively, so that is electrostatically confines that electron beam to a small area of the anode

Question 43

most rotating anodes have __ filaments

Answer 43

2, a large and a small focal spot

Question 44

grid-controlled tubes are designed to:

Answer 44

turn on and off rapidly

Question 45

*x-ray tube current is adjusted by:

Answer 45

controlling the filament current

Question 46

because electrons carry negative charges:

Answer 46

they repel one another and tend to form a cloud around the filament

Question 47

this cloud of electrons is called _____ and it:

Answer 47

space charge, it makes it difficult for other electrons to be emitted by the filament b/c of electrostatic repulsion (electrons are stuck at the cathode end b/c they are attracted to the focusing cup)

Question 48

*thermionic emission at ___ kVp and ___ mA can be space charge limited

Answer 48

low kVp and high mA

Question 49

saturation current:

Answer 49

at any given filament current, the x-ray current rises with increasing voltage to a maximum value, a further increase in kVp doesn't result in a higher mA because all available electrons have been used

Question 50

filament current is measured in ____ | tube current is measured n ____

Answer 50

A | mA (technique factor)

Question 51

small FS is used when, measurement:

Answer 51

better spatial resolution is required, 0.1-1mm

Question 52

large FS is used when, measurement:

Answer 52

large body parts or when techniques that produce high heat are used, 0.3-2mm

Question 53

stationary anodes are used in:

Answer 53

dental, portables, and special units where high tube current and power are NOT required

Question 54

*the anode does 3 things:

Answer 54

conducts electricity, radiates heat, and contains the target

Question 55

the anode receives electrons emitted by the cathode and conducts them through the tube and back to the _____

Answer 55

high-voltage generator

Question 56

the anode is a ______, and also provides ______, and must be a good ______

Answer 56

electrical conductor, mechanical support for the target, thermal dissipator

Question 57

more than __% of _____ turns into heat

Answer 57

99% of electron kinetic energy

Question 58

most common anode materials:

Answer 58

copper, molybdenum, and graphite

Question 59

in STATIONARY ANODES the target is:

Answer 59

tungsten alloy embedded in a copper anode

Question 60

in ROTATING ANODES the target is:

Answer 60

a rotating tungsten disc

Question 61

tungsten is used for the target for 3 reasons:

Answer 61

- high atomic # (74), high energy x-rays - thermal conductivity, efficient metal for dissipating heat - high melting point, 3,400C can withstand high tube current

Question 62

the rotating anode provides ____ times more _____

Answer 62

500x more area to interact with electron beam

Question 63

*____ tube current and _____ exposure times are possible with the rotating anode

Answer 63

high tube current and shorter exposure times

Question 64

*the focal spot size is the:

Answer 64

actual x-ray source

Question 65

*line-focusing principle:

Answer 65

by angling the target, the effective area is much smaller than the actual area

Question 66

target angles can vary from ______

Answer 66

5-20 degrees

Question 67

the intensity of the x-rays emitted on the heel end of the target are:

Answer 67

reduced because they have a longer path and increased absorption

Question 68

*the smaller the angle, the ___ the heel effect

Answer 68

larger

Question 69

at the CR the beam intensity is __%

Answer 69

100%

Question 70

at the cathode side the beam intensity:

Answer 70

can be up to 120%

Question 71

at the anode side the beam intensity:

Answer 71

can be as low as 75%

Question 72

positioning the cathode end over the _____ anatomy provides _____

Answer 72

thickest anatomy provides more uniform exposure (density)

Question 73

*heel effect results in ___ effective FS and ___ radiation intensity on the anode side of the beam

Answer 73

smaller effective FS and less radiation intensity

Question 74

radiation:

Answer 74

transfer of heat by emission of infrared radiation

Question 75

conduction:

Answer 75

transfer of energy from one area of an object to another

Question 76

convection:

Answer 76

transfer of heat by the movement of a heated substance from one place to another

Question 77

*excessive heat results in:

Answer 77

reduced tube life

Question 78

*maximum techniques should:

Answer 78

never be applied to a cold anode

Question 79

*most frequent cause of abrupt tube failure is:

Answer 79

electron arcing from the filament to the enclosure because of tungsten vaporization

Question 80

radiographic rating chart tells you:

Answer 80

which techniques are safe to use and which are not safe to use for x-ray tube operation

Question 81

in the rating chart the x & y axis are:

Answer 81

kVp & time

Question 82

the curve represents:

Answer 82

tube currents in mA

Question 83

any combo of kVp & time that is below the mA curve is:

Answer 83

safe to use

Question 84

anode cooling chart tells you:

Answer 84

the thermal capacity of the anode (maximum heat capacity) and determines the length of time required for complete cooling

Question 85

single phase HU=

Answer 85

kVp x mA x s = 0.7J

Question 86

3 phase/high frequency HU=

Answer 86

kVp x mA x s = 1J

Question 87

complete cooling of the housing requires ___ hours

Answer 87

1-2 hours