what technical factor pushes electrons across the from cathode side to the tungsten anode rotating disk
What is the focal point
a specific area or spot located on the rotating anode disk
What will happen eventually to the anode rotating disk or to a specific area on the focal track
the focal track material will begin to vaporize which causes the area to roughen or pit
what does pitting do to the rotating anode disk
it reduces the efficiency of the tube
what process or change in focal track allows one to describe how old the focal track's tube is
from the pitting that has occurred from years of wear and tear
What happens to tungsten overtime
what happens inside the xray tube because of excessive use of the disk
it begins to vaporize
it becomes gassy and produces less efficient x ray photons
what exactly causes wear and tear of the focal track
high usage of mAs or electrons
if you are using an old machine in order to do a chest xray, what technical factor must be changed?
you have to double the mAs because since the machine is old you need more electrons to make out the image which produces more radiation than if it was a new machine
what causes a melting spot on the focal track (2 reason)
when rotor fails to rotate the anode and also due to heat damage
What is it called when you need to preheat the xray tube prior to taking any exposures?
anode warm up procedure
What is the average kVp and mA of a normal warmup procedure
How many exposures are required for the warmup phase
100 or 200 mA
3 exposures each 1 second a part
what happens if you do not warm up the xray tube
you can cause the anode disk to crack because of sudden pile up of heat
what is the focal track
is the circular path on the anode that will be impacted by the electron stream
what are the alternative names for the target area
focal spot focal point or focal track
Is the focal spot the same as the filament
yes small filament small focal spot
large filament large focal spot
which is a bigger filament .6 FSS or 1.2 FSS
what is the actual focal spot
the physical area of the focal track that is impacted
what is the effective focal spot
the area of the focal spot that is projected out of the tube and down to the object being radio graphed
which focal spot happens first the actual or the effective?
what is the average angle range of the anode rotating disk
What main phrase is the THE LINE FOCUSING PRINCIPLE based on
what does this do to the image ?
"when the angle of the anode is less than 45 degrees the effective focal spot sizewill always be smaller than the actual focal spot size (physical area)"
provide even more clarity of the image
What causes the line focus principle to happen
the design or the geometry of the anode target area is angled
what is the purpose of the line focus principle
to reduce the effective focal spot and will allows for the best resolution of detail
what determines the sized of the effective focal spot?
the actual focal spot
what controls the size of the actual focal spot?
the length of the filament
what happens when the actual focal spot size increases?
the effective focal spot increases as well but still remains smaller than the actual FSS
what is the most common target angle on a rotating disk
Can a 12 degree anode target area cover a 14x17 cassette at a 40'' SID
what is the largest cassette size
14x17 mostly used for abdomens
if we increase mAs too much using a small filament what will happen?
what do we use instead
although the machine wont let this happen, the small filament will not be able handle the massive amts of electrons
so instead we would use a larger filament
Can small focal spot sizes utilize high mA stations
what is the anode heel effect?
because of the geometry of the angle target area the radiation is intensifies on the cathode side
why does the anode heel effect happen?
this happens b/c once the kVp pushes all the electrons over to the anode side the photons are more likely to be absorbed by the target material (located at the back of anode disk )
thus less photons are on the anode side and they are now exiting towards the cathode side
B/c of the anode heel effect how much more photons can wind up being on the cathode side and anode side?
20% more on cathode side 25% less on anode side
What is the SID?
source to image distance
when is the anode heel effect more noticeable?
when large film sizes are used at a short distance (refer to note book if you dont remember)
In regards to the anode heel effect, why do radiographic tables have a head end?
so the least amount of photons being emitted towards the head which means less radiation exposure
How would you use the anode heel effect to your advantage
when imaging thicker denser body parts, position the patient so that the cathode is over the bigger body parts thus it will recieve more radiation to make a better picture exposure is not a extreme factor b/c the body part is bigger you need more radiation
what major is composed of the stator
induction motor magnets that turn the anode
what are the two switches to be depressed when taking an image
what is the only part of the x-ray tube located outside the glass envelope?
how is it able to function outside the tube?
the electromagnetic effects that cause the rotor to turn can function through the glass
what happens when the rotor switch is pressed?
it sends a current to the stator which then causes the rotor to turn the anode
what happens if the stator is not functioning?
the anode will not rotate resulting in the immediate melting of a spot on the target
where is the rotor located
inside the stator and inside the glass envelope
what is the rotor composed of
made of hollow copper cylinder and is attached to the anode disk by a molybdenum shaft
what is the purpose of the ball bearings
used as lubricants between the cylinder (or cuff) and the anode shaft to facilitate the turning of the anode disk
what do you hear when the rotor switch is depressed
ball bearings turning at high speed
what does the stator do at the end of an exposure
it runs in reverse to slow down the velocity (speed) of the rotor
What parts are comprised of the the entire glass envelope
the anode and cathode assembly
but the stator is located outside the tube and glass envelope
what is the glass envelope made out of?
why is it sealed tight?
different types of heat resistant Pyrex glass
to maintain a high vacuum
how thick is the window segment of the glass envelope where the primary beam exits
what is the function of the glass envelope
maintain the vacuum between the cathode and anode side
what happens when you remove most of the air in the vacuum (hence its function)
and does what to the xrays
it allows the electrons flow from - end to + end without encountering gas/air atoms which increases the efficiency of the tube operation
what is the protective housing the xray tube is made out of
what does the steel housing control? (2 things)
leakage radiation and scatter radiation
how does the protective housing provide a means to control the tube?
by isolating high voltages
what is lined on the inside of the steel housing
what substance is found between the housing and lead lining
what is the purpose of the dilectric oil
insulates the high voltage components of the tube housing aand absorbs much of the heat
What is the specific term on how x-rays are produced at the anode
isotropically (in all directions)
where are unwanted photon beams absorbed?
what is the primary beam?
by the housing
the primary beam consists of photons emitted through the glass window and housing window
what is leakage radiation
any photons that escape from the housing except at the window
leakage radiation must no exceed what length
100mR/hr at 1 meter
what is mR
what is another role of the protective housing
protection of roughhousing by the radiographer
is a patient or xray tech allowed to touch the housing during exposure
the dielectric oil is found between what two structures
the glass envelope and the protective housing
what is off focus radiation
consists of photons that were not produced at the focal spot
when does off focus radiation happen
when high voltage electrons striking the target area produce scattered electrons or photons
can off focus radiation strike other areas of the tube that can produce xray photons as well
what absorbs most of the off focus radiation
what is the outcome of off focus radiation what do they do to the image
What is the difference between scatter radiation
these photons create a "ghosting effect"
does not produce images like the off focus radiation
what percentage of the primary beam is contributed to the off focus radiation
how powerful are the off focus radiation photon beams
not power low energy than primary beam
what is the purpose of cooling curves and tube rating charts?
used as safety measure to avoid thermal damage to the tube
Any combination of technical factors on or under the curve is to be considered what?
what are the three types of charts and cooling curves