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Chap 6. Tube

Equipment. Chap 6. X-ray tube

QuestionAnswer
Modern x-ray tube? First tube? coolidge. First was crookes
filaments are usually made of _________. Why? thoriated tungsten. High melting point
x-ray tube current is adjusted by controlling the _______ _______. filament current
Space charge is electrons forming a thermionic cloud around filament, they build up and their neg charge repels new electrons to be emitted.
when is the small filament used? The larger? 300 mA or less for small, 400 mA or more for larger
Small focal spots range is from __ to ___. Large is from ____ to ____. .1-1mm. .3-2mm.
The anode serves 3 functions: receives e-/target, conducts electricity, thermal dissipater.
most rotating anodes revolve at 3400 rpm. High capacity rotates at 10,000 rpms.
Tungsten symbol, atomic number, K shell energy (keV), melting temp. W, 74, 69, 3400 degrees C.
What is the stem of the anode made of? molybdenum
What turns the anode? electromagnetic induction motor, consists of anode and stator.
Stator is _________, rotor is _______. outside, inside. ***** (equipment book has this backwards.. check prev. tests and prev. books stator is OUT rotor is IN.) *****
best degree target angle? 12 (normal is between 7-20)
What is the focal spot? What is the effective focal spot? actual x-ray source.. the area of the TARGET from which x-rays are emitted. Effective is area projected onto the patient and IR.
As the size of the focal spot decreases, the heating of the target is... concentrated onto a smaller spot... not good.
What is the line focus principle? By angling the target, one makes the effective focal of the target smaller than the actual focal spot.
When the target angle is made smaller, the effective focal spot size..... is also made smaller.
What is the heel effect? the intensity of x-rays that are emitted through "heel" of the target is reduced because they have a longer path through the target and therefore increased absorption. (Steeper the angle the larger the heel effect.. cathode more intense than anode side)
The smaller the anode angle, the larger the ____ heel effect
In chest rad, the cathode should always be _____. In abdominal, the cathode should be _____. inferior, superior. (cathode always over thicker portion)
the effective focal spot is smaller on the ______ side of the x-ray field. anode
The heel effect results in smaller _________ focal spot and less radiation intensity on the ____ side of the beam. effective, anode
Transfer of energy from one area of an object to another is termed conduction
transfer of heat by movement of a heated substance from one place to another is termed convection
3 types of x-ray tube rating charts: radiographic rating chart, anode cooling chart, and housing cooling chart.
Which chart is the most important because it conveys which techniques are safe and which are unsafe for tube operation. radiographic rating chart
single phase heat unit formula? HU= kVp x mA x s = 0.7J
exam of lumbar spine with single phase imaging system requires 98kVp, 120 mAs. How many heat units are generated by this exposure? HU= 98kVp x 120mAs = 11,760 HU
Three phase/high frequency heat unit formula? HU= 1.4 x kVp x mA x s = 1J
One heat unit is = to ____ Joule one
6 skull films are exposed with a 3phase generator operated at 82 kVp, 120 mAs. What is the total heat generated? HU = 1.4 x 82 kVp x 120 mAs =13,776 HU. =6 x 13,776 HU = 82,565 HU
The thermal capacity of an anode and its heat dissipation characteristics are contained in a rating chart called an anode cooling chart
Protective housing of a tube has 3 purposes: reduces leakage radiation, provides mechanical support, conducts heat away from tube target
How many heat units are generated by an exposure of 70 kVp, 300 mA, and 0.1 second on a 1f rectified unit? 2100HU
Created by: Zoest35