X-Ray Equipment in Dental Practice
All X-ray machines consist, generally speaking, of the same components. Figure 1.1 is a schematic illustration of an X-ray machine.
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X-Ray Equipment in Dental Practice
1.1
The X-Ray Machine
All X-ray machines consist, generally speaking, of the same components. Figure 1.1 is a schematic illustration of an X-ray machine. (a) Vacuum glass tube Inside the vacuum glass tube, one can find the cathode, which looks like an incandescent light bulb’s filament. This cathode is negatively charged. The number of electrons is determined by the amperage (usually milli-ampere or mA). The number of electrons is proportionate to the number of X-rays and hence to the X-ray dose as well. Opposite to the cathode is the positively
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Both cathode and anode are made of TUNGSTEN. The vacuum tube allows the electrons to travel from the cathode to the anode with the least resistance, to keep their energy. Only 1% of the collisions is converted into X-rays and 99% is heat production.
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OIL Vacuum X-ray tube
Oil contained in a rubber bag that allows expansion when the oil is heating up. Too much expansion causes the bag to trigger a micro switch to turn off the machine until it is safe to be used again.
Spacer cone / beam indicating device [email protected]
Fig. 1.1 Schematic drawing of an X-ray machine © Springer Nature Switzerland AG 2019 J. Aps, Imaging in Pediatric Dental Practice, https://doi.org/10.1007/978-3-030-12354-3_1
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1 X-Ray Equipment in Dental Practice
charged anode. Both anode and cathode are made of tungsten (W). The electrons are attracted to the anode due to a high voltage across both. Due to the vacuum glass tube, the electrons will not collide with air before hitting the anode (target). Due to the law of conservation of energy, the colliding electrons produce 99% heat and 1% X-rays. The penetration power of the X-rays is determined by the voltage across the tube (usually expressed as kilovoltage). Medical X-ray machines have a rotating anode to dissipate the heat better, as they use longer exposure times, higher kV, and mA settings. Step-up transformer The step-up transformer steps up the grid’s power to the necessary kilovoltage (kV). Some dental X-ray machines allow for the kV to be changed; most intraoral machines have a fixed voltage. For intraoral X-ray machines the kV should be between 60 and 70 kV. Cooling oil Since 99% of the collisions between the electrons and the target produce heat, the machine requires to be cooled. The oil is contained in a rubber bag, which, if expanded too much due to heat absorption, is able to push a microswitch to temporarily disable the machine so no subsequent exposure can be made. The machine will be ready for use when it has cooled down again. Lead casing The lead casing prohibits X-rays from leaking from the machine while it is in use. Only X-rays going through the porthole are supposed to leave the machine. Filter An aluminum filter is placed in front of the porthole to filter out all the lower energy X-rays, which otherwise would just be absorbed by the patient and which would not contribute to the diagnostic image. The manufactu
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