From my previous post, I have discussed the three main components of the x-ray imaging system, which are the x-ray tube, operating console and the high voltage generator. Now, I’m going to present a brief discussion on the most important component of the imaging system – the x-ray tube. This, likewise, includes a simple explanation on how x-rays are produced inside the x-ray tube.

The x-ray machine is made up of a cathode, the negative side, and an anode, the positive side, that is enclosed in a glass or metal envelope. The machine passes current through the cathode (due to current supplied to it by adjusting the mAs), which heats it up and emits electrons off the surface (aka Thermionic Emission – the giving off of electrons from a heated surface). Cathode is primarily composed of filaments (large and small) – the one that actually emits electrons when heated – and a focusing cup – which condenses the electrons into a smaller area. Focusing cup is usually made of thoriated tungsten.

The anode, which is made of tungsten, draws electrons across the tube. The electrons fly through the tube with extreme force due to the voltage difference between the cathode and the anode. An electron is knocked loose from a lower orbital when an electron collides with a tungsten atom. This causes the emission of an x-ray.

The x-ray tube is surrounded by a thick lead shield or a glass/metal envelope. This is done to prevent the x-rays from going in all direction. There is a small slit in the end of the machine that allows a beam of electrons to escape toward the patient, which is called the WINDOW, where the useful x-ray beam passes. Other x-rays that escape the tube without passing the window is called leakage radiation.