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X-ray Tubes

X-ray tube test 6/2

QuestionAnswer
what is the filament made of? tungsten = cause it has a high atomic #(74), heating point (3410), k-edge (69)
what is the focusing cup made of? negatively charged metal = like nickle
what is the disadvantage of vaporization of tungsten? it settles on the bottom of the tube and acts as filtration and can cause arching
what is a gassy tube? when you break the vacuum seal, so much disruption will make the x-ray blank (no exposure) or arching (sparks) and eventually will break
what is the purpose of the vacuum tube? its air tight to not allow disruption of e-'s
what is the purpose of the focusing cup? it focuses the e- beam
what is the purpose of the anode? produces x-ray, provides mechanical support for target,
what is the purpose of the cathode? produces e-beam
what is the purpose of the tube warm-up? it prevents thermal damage
what is the purpose of line focusing principle? as the target angle decreases, so does the effective FSS (DIRECT) - target angle allows for a larger actual FS & provides a smaller effective FS
what is the purpose of the rotating anode? it rotates so the e- stream doesnt always hit the same spot to prevent pitting
what is the purpose of the tube housing? its acts as a ground to prevent a shock
state the melting point, Z#, and k-edge of tungsten? melting point = 3410 degrees, Z# (atomic #) = 74, k-edge = 69 keV
state the purpose of a dual focused x-ray tube? it has a 2 filaments = allows for small FSS & large FSS
how would you calculate the heat units for a one phase unit? mA x time x kVp
how would you calculate the heat units for a 3 phase 6 pulse unit? mA x time x kVp x 1.35
how would you calculate the heat units for a 3 phase 12 pulse unit? mA x time x kVp x 1.44
what is a manual warm-up procedure? 100 mA, 1 sec, 65-70 kVp, large FSS
what is the difference between actual and effective focal spot sizes? actual FSS = target exposed to e- , effective FSS = area projected onto pt & IR
list the most common tube anode angle and the effect of angle size on focal spot size? 12 degrees (it ranges from 5-15 degrees) - a smaller angle = smaller FSS -vice-versa-
Define tube current? flow of e-'s across tube
State the amperage and voltage ranges used to heat the filament? amperage = 3-5 amps ........ volts = 6-10 volts
What is the component that sits outside the glass envelope of the tube? stator (of the rotor of the motor)
What device controls kVp selection in the circuit? autotransformer
list the range of rpm's that the anode rotates? 3,400 - 10,000 rpm
define leakage/off-focus radiation, the standard level allowable in mR/hr? = any radiation off the focal track - the FDA says the housing must reduce amount to <100mR/hr at 1 m
what is the difference of scattered radiation and off-focus radiation on an image? scattered radiation = happens in pt (fog) ............ off-focus radiation = happens in tube (ghosting)
what are methods to lengthen tube life? warm-up and excessive rotoring
what amount of lead is the protective housing made of? 1.5mm Pb
what is the purpose of oil? helps dissipate heat
what is a diode? it has 2 electrodes = + anode & - cathode
what is the tube we use today called? coolidge (old = cold cathode/crookes tube)
what does the rotor work off of? electromagnetic(EM) mutual induction
does more SID have more or less beam divergence? less
what are 3 ways heat can be dissipated from rotating anode? 1.) radiation = transfer of heat by the emission of infrared radiation 2.) conduction = transfer of energy from one area of an object to another 3.) convection = transfer of heat by the movement of a heated substance from one place to another
The protective housing is made of _______. 1.5 mm Pb
Area where the useful beam exits. window or port
Leakage radiation is reduced to _____________ by the ___________. 100 mR/hour at 1 meter, protective housing
What is th purpose of the protective housing? protect against shock.
Dissipates heat away from the tube and serves as an insulator. Oil or Fan cooled
What are some functions of the Anode? conducts electrons through the tube, provides mechanical support for target, good thermal radiator - dissipates heat to prevent pitting or cracking
What is tube tanning? tungstate filament deposits on bottom of tube acting like added filtration
Isotropically xrays emitted with equal intensity in all directions
Area projected onto patient and IR. Effective FSS
Target area exposed to electrons. Actual FSS
What is the purpose of the target angle? Allows for a larger actual FS and provides a smaller effective FS
What is the manual tube warm-up procedure? 100 mA, 65-75 kVp, Large FSS, 3-5 exposures, 1 sec. exp. time
What is the anode heel effect? Decrease xray intensity on anode side of useful beam because of absorption in heel of target
What are the two types of anodes? rotating and stationary
Stator is located ______ the envelope and the Rotor is located _______ the tube. outside, within
What is the most common cause of tube failure? tungsten vaporization
Holds filament, contains negative charge and focuses electrons onto target of anode. focusing cup
What is leakage radiation? Xrays that escape the protective housing
What is the equation used to determine how many heat units are produced with one exposure in a single phase unit? mA x time x kVp
What is the equation used to determine how many heat units are produced with one exposure in a 3 phase 6 pulse unit? mA x time x kVp x 1.35
What is the equation used to determine how many heat units are produced with one exposure in a 3 phase 12 pulse unit? mA x time x kVp x 1.41
Line focus principle by angling the target you are allowing a large area for heating but still maintaining a small focal spot size for improved spatial resolution
Created by: sr4095