X-Ray Tube Support System

• The external structure of the X-ray tube includes support structure, protective housing, and glass or metal enclosure
• Due to the weight of the X-ray tube and housing assembly it requires a support mechanism for the radiologic technologist to position it

Ceiling Support System

• This is the most frequently used support system
• It consists of two perpendicular sets of ceiling-mounted rails allowing for both longitudinal and transverse movement of the X-ray tube
• A telescoping column attaches the X-ray tube housing to the rails, which allows for variable source-to-image receptor distance (SID)
• When centered above the table at the standard SID, the X-ray tube is in a preferred detent position
• Positions can be selected and locked by the radiologic technologist
• Some ceiling-supported X-ray tubes have a control to remove all locks, which allows the tube to "float" for adjustments
• The floating mode should only be used for minor adjustments, with a limit of about 1 meter to avoid arm and shoulder strain

Floor-to-Ceiling Support System

• This has a single column with rollers at each end, one attached to a ceiling mounted rail and the other attached to a floor-mounted rail
• As the column rotates, the x-ray tube slides up and down the column
• In a variation of this system the column is positioned on a single floor support system with one or two floor-mounted rails

C-Arm Support System

• Interventional radiology suites are often equipped with C-arm support systems which are shaped like a "C"
• These systems are ceiling-mounted and allow for very flexible X-ray tube positioning
• The image receptor is attached to the opposite end of the C-arm from the X-ray tube
• Variations of the C-arm system include L-arm or U-arm support systems

Protective Housing

• Protective housing guards against excessive radiation exposure and electric shock
• X-rays are emitted isotropically, meaning with equal intensity in all directions
• Only the X-rays emitted through the window of the X-ray tube are used and called the useful beam
• Leakage radiation refers to the X-rays that escape through the protective housing, contributing to unnecessary exposure without providing diagnostic value
• A properly designed protective housing reduces leakage radiation to less than 1 mGya/h at 1 meter under maximum conditions
• The protective housing also has high-voltage receptacles to prevent accidental electric shock, which protects against electrocution risks for early radiologic technologists
• The housing provides mechanical support for the X-ray tube and protects it from damage due to rough handling
• Some protective housings contain oil for electrical insulation and thermal cushion to dissipate heat
• Some housings include a cooling fan to air-cool the tube or the oil
• A bellows-like device allows the oil to expand when heated, and if the expansion is excessive, a microswitch prevents tube use until it cools

Glass or Metal Enclosure

• X-ray tubes are designed with a glass or metal enclosure
• X-ray tube is an electronic vacuum tube with components inside a glass or metal enclosure
• It contains two electrodes: the cathode and the anode
• The tube is relatively large, about 30-50 cm long and 20 cm in diameter, and the glass enclosure is made of Pyrex to withstand heat
• The vacuum inside the tube promotes more efficient X-ray production and longer tube life
• A small amount of gas inside reduces electron flow and increases heat generation
• Early X-ray tubes, modifications of the Crookes tube, were not vacuum tubes and contained controlled amounts of gas
• The modern Coolidge tube is a vacuum tube, and if it becomes gassy, X-ray production falls and the tube may fail
• Metal-enclosed tubes are an improvement over glass ones, as glass tubes age, tungsten vaporizes and coats the inside, causing electrical issues and tube failure
• Metal enclosures maintain a constant electric potential, which leads to longer life and fewer failures, so most high-capacity X-ray tubes now use metal enclosures
• The X-ray tube window is a thin area measuring about 5 cm² in the enclosure through which the useful beam of X-rays is emitted, minimizing absorption