x ray tube

Question 1

what tube was designed in the early 1870’s (ob 1)

Answer 1

Crooke’s tube

Question 2

which side of he tube is positive (ob 1)

Answer 2

the anode side

Question 3

which side of the tube is negative (ob 1)

Answer 3

the cathode side

Question 4

when were x rays discovered (ob 1)

Answer 4

november 8, 1895

Question 5

who discovered fluoroscopy & when (ob 1)

Answer 5

thomas Edison in 1896

Question 6

what tube was created in 1913 (ob 1)

Answer 6

the coolidge tube (we use this today)
first to use hot cathode & vacuum in glass

Question 7

what are the 4 factors needed to create x rays (ob 2)

Answer 7

1. electrons
2. a target material
3. high voltage
4. Vacuum

Question 8

what is the high voltage needed to do? (ob 2)

Answer 8

accelerate the electrons in the xray rube

Question 9

what is the vacuum needed for? (ob 2)

Answer 9

makes absence of air so electrons can travel

Question 10

what does the glass envelope do? (ob 3)

Answer 10

houses internal components
creates the vacuum
made of pyrex glass

Question 10

what is the cathode assembly (ob 3)

Answer 10

negative charged portion of tube
source of electrons
-includes filament wire and focusing cup

Question 11

what is the cathode filament made of? (ob 3)

Answer 11

Tungsten (W)

Question 12

what does filament size determine? (ob 3)

Answer 12

focal spot size

Question 13

what does the focusing cup do? (ob 3)

Answer 13

directs a stream of e- toward the target (anode)

Question 14

what is the anode (ob 3)

Answer 14

the positively charged side of the tube

Question 15

what is the anode surface disc made of? (3)

Answer 15

tungsten (W)

Question 16

Tungsten (W) has a melting point of what? (3)

Answer 16

6200 degrees F

Question 17

what is the focal tract? (3)

Answer 17

the area on anode disc that e- hit

Question 18

what is the stator? (3)

Answer 18

magnets on outside of tube that causes rotor & anode to rotate w/o contact

Question 19

how fast does the stator rotate (3)

Answer 19

3300-10,00 rpm (revolutions per minute)

Question 20

what is the protective housing? (3)

Answer 20

lead lined metal housing that keeps xrays from being emitted in all directions with insulated oil to keep the tube cool

Question 21

Line focus principal is the relationship between what? (4)

Answer 21

the e- stream size & angle of anode disc to create a large or small focal spot

Question 22

what is the range for xray tube anode disc angles (4)

Answer 22

6-18 degrees

Question 23

what is actual focal spot (AFS) (4)

Answer 23

the physical space on the anode where e- strike determined by filament size

Question 24

a large filament AFS allows for what? (4)

Answer 24

High mA, short time
large body parts
less on tube
LOW image resolution

Question 25

a small filament AFS allows for what? (4)

Answer 25

Low mA, longer time
smaller body parts
More on tube
HIGH image resolution

Question 26

what is effective focal spot (EFS)(4)

Answer 26

the width of the xrays coming from the focal tract

Question 27

what are the 2 controlling factors of Effective focal spot (4)

Answer 27

Large filament & Large anode angle = Large EFS

Question 28

why will EFS always be smaller than AFS (4)

Answer 28

because of the anode angle

Question 29

a large EFS results in what kind of spatial resolution (5)

Answer 29

Low spatial resolution (blurry)

Question 30

a small EFS results in what kind of spatial resolution(5)

Answer 30

High spatial resolution (clear)

Question 31

what is thermionic emission (5)

Answer 31

an electrical current that causes filament to heat up
amount of e- given off is based on mA (rotor phase)

Question 32

what is electron travel (5)

Answer 32

Very high voltage between cathode- and anode +
when exposure is made

Question 33

what happens when electrons strike the focal track while the anode disc is tuurning (5)

Answer 33

e- kinetic energy is converted into
x ray photons & heat

Question 34

how does a large angle effect AHE (6)

Answer 34

Less AHE
more equal exposure across the field

Question 35

how does small angle effect AHE (6)

Answer 35

More AHE
more variation in exposure across the field

Question 36

when is AHE more pronounced ? (6)

Answer 36

shorter SID
large field size

Question 37

what is off focus radiation? (6)

Answer 37

e- that hot outside the focal spot to create x rays that cause anatomical structures to be seen

Question 38

how does off focus radiation effect diagnostic value, spatial resolution (blur) & patient does (6)

Answer 38

adds no diagnostic value
decreases spatial resolution
increases pt dose

Question 39

what is the heat produced in AHE measured in (7)

Answer 39

AHU

Question 40

what are the major contributing factors of AHU? (7)

Answer 40

kVP & mAs

Question 41

what does AHU= (7)

Answer 41

AHU= kVp x mAs x 1.41
(70kVp @100 mAs = 9870 AHU)

Question 42

describe a filament failure (8)

Answer 42

tungsten in filament evaporates

Question 43

describe arcing

Answer 43

evaporated tungsten settles inside glass envelope
creates electrical arc between the filament and coated glass (shatters glass)

Question 44

describe a damaged anode

Answer 44

pitted or crack in anode from really big exposure on cold anode or bad bearings from rotor

Question 45

what technique do you use for a tube warm up

Answer 45

low kv
low mA
high seconds (80 kVp x 200 mA x 1 sec)