The main component of an X-ray machine is a vacuum tube with a cathode, or filament, and an anode, which is typically made of tungsten. Electric current passes through the filament, bringing it up to an extremely high temperature. Once it reaches a certain level of energy, the filament begins emitting negatively charged electrons from its surface. The positively charged tungsten anode attracts these electrons with great force, drawing them through the vacuum tube at a high speed. When an electron collides with a tungsten atom, an electron in one of the atom’s lower orbitals gets knocked away. An electron from a higher orbital takes the place of the dislodged electron, releasing energy as an X-ray photon during its descent. The X-ray machine is encased in thick, protective lead shielding, which prevents these X-ray photons from escaping. A small window in the shield allows some X-ray photons to exit as a narrow beam is directed toward the patient. When X-rays hit the patient’s body, some pass through and some are blocked. Typically, bone blocks the X-rays, while soft tissue allows them to proceed. An X-ray camera captures the X-rays that pass through the patient, forming an image on a piece of film.
This standard procedure creates excellent images of bone matter and other hard solids, allowing doctors to diagnose broken bones, foreign bodies and other conditions. However, most soft body tissues aren’t very clear in X-ray pictures. A doctor who needs to examine an organ or blood vessel must introduce special liquids called contrast media into the body. These liquids absorb X-rays better than the surrounding tissues. To focus on digestive and endocrine organs, for instance, the patient must swallow a contrast media - usually a barium compound. To focus on blood vessels, doctors inject the contrast media directly into the bloodstream. Doctors frequently use contrast media in fluoroscopy, which is when a live X-ray image is used for tracing the movement of contrast media within the body.
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