x ray tube Flashcards
what tube was designed in the early 1870’s (ob 1)
Crooke’s tube
which side of he tube is positive (ob 1)
the anode side
which side of the tube is negative (ob 1)
the cathode side
when were x rays discovered (ob 1)
november 8, 1895
who discovered fluoroscopy & when (ob 1)
thomas Edison in 1896
what tube was created in 1913 (ob 1)
the coolidge tube (we use this today)
first to use hot cathode & vacuum in glass
what are the 4 factors needed to create x rays (ob 2)
- electrons
- a target material
- high voltage
- Vacuum
what is the high voltage needed to do? (ob 2)
accelerate the electrons in the xray rube
what is the vacuum needed for? (ob 2)
makes absence of air so electrons can travel
what does the glass envelope do? (ob 3)
houses internal components
creates the vacuum
made of pyrex glass
what is the cathode assembly (ob 3)
negative charged portion of tube
source of electrons
-includes filament wire and focusing cup
what is the cathode filament made of? (ob 3)
Tungsten (W)
what does filament size determine? (ob 3)
focal spot size
what does the focusing cup do? (ob 3)
directs a stream of e- toward the target (anode)
what is the anode (ob 3)
the positively charged side of the tube
what is the anode surface disc made of? (3)
tungsten (W)
Tungsten (W) has a melting point of what? (3)
6200 degrees F
what is the focal tract? (3)
the area on anode disc that e- hit
what is the stator? (3)
magnets on outside of tube that causes rotor & anode to rotate w/o contact
how fast does the stator rotate (3)
3300-10,00 rpm (revolutions per minute)
what is the protective housing? (3)
lead lined metal housing that keeps xrays from being emitted in all directions with insulated oil to keep the tube cool
Line focus principal is the relationship between what? (4)
the e- stream size & angle of anode disc to create a large or small focal spot
what is the range for xray tube anode disc angles (4)
6-18 degrees
what is actual focal spot (AFS) (4)
the physical space on the anode where e- strike determined by filament size
a large filament AFS allows for what? (4)
High mA, short time
large body parts
less on tube
LOW image resolution
a small filament AFS allows for what? (4)
Low mA, longer time
smaller body parts
More on tube
HIGH image resolution
what is effective focal spot (EFS)(4)
the width of the xrays coming from the focal tract
what are the 2 controlling factors of Effective focal spot (4)
Large filament & Large anode angle = Large EFS
why will EFS always be smaller than AFS (4)
because of the anode angle
a large EFS results in what kind of spatial resolution (5)
Low spatial resolution (blurry)
a small EFS results in what kind of spatial resolution(5)
High spatial resolution (clear)
what is thermionic emission (5)
an electrical current that causes filament to heat up
amount of e- given off is based on mA (rotor phase)
what is electron travel (5)
Very high voltage between cathode- and anode +
when exposure is made
what happens when electrons strike the focal track while the anode disc is tuurning (5)
e- kinetic energy is converted into
x ray photons & heat
how does a large angle effect AHE (6)
Less AHE
more equal exposure across the field
how does small angle effect AHE (6)
More AHE
more variation in exposure across the field
when is AHE more pronounced ? (6)
shorter SID
large field size
what is off focus radiation? (6)
e- that hot outside the focal spot to create x rays that cause anatomical structures to be seen
how does off focus radiation effect diagnostic value, spatial resolution (blur) & patient does (6)
adds no diagnostic value
decreases spatial resolution
increases pt dose
what is the heat produced in AHE measured in (7)
AHU
what are the major contributing factors of AHU? (7)
kVP & mAs
what does AHU= (7)
AHU= kVp x mAs x 1.41
(70kVp @100 mAs = 9870 AHU)
describe a filament failure (8)
tungsten in filament evaporates
describe arcing
evaporated tungsten settles inside glass envelope
creates electrical arc between the filament and coated glass (shatters glass)
describe a damaged anode
pitted or crack in anode from really big exposure on cold anode or bad bearings from rotor
what technique do you use for a tube warm up
low kv
low mA
high seconds (80 kVp x 200 mA x 1 sec)
