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what is the focusing cup made of?
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X-ray Tubes
X-ray tube test 6/2
| Question | Answer |
|---|---|
| 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
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