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X-rays were discovered accidentally by the Germany Physicist William Roentgen in 1895, while experimenting with electron beams in a gas discharge tube. He discovered that a screen in the laboratory started glowing when the electron tube was turned on, and continued to glow even after the tube was covered with a black cardboard. He placed his hand and saw a silhouette of his bones projected onto the fluorescent screen; indicating that the radiation had penetrated through the tissue except the bones. This remarkable discovery marked the beginning of advances in diagnostic techniques for examining broken bones, cavities, swallowed objects, etc. using X-rays.
The atoms in our body absorb visible light photons but X-ray photons pass through as they have high energy, however calcium ions in the bones absorb X-ray photos. An image of the bones can be obtained on a photographic plate placed behind the part to be viewed and opposite to the X-ray beam.
X-rays are produced in thermionic tubes or valves (vacuum tubes).
The vacuum tube consists of a heated filament, an accelerating anode (positive terminal), and a heavy metal target. The heated filament emits electrons. The electrons are accelerated by accelerating anode. The high energy electrons bombard a heavy metal target to release electromagnetic waves (X-rays) of varying frequencies.
The kinetic energy ½ mv2 on collision is converted to hfmax, highest energy is released with greatest loss of kinetic energy.
The spectrum shows spikes called characteristic lines generated from radiation due to electrons from lower energy levels being raised to higher energy levels in atoms of the target material. If the accelerating voltage is increased, the highest frequency is increased. These are hard X-rays. If the filament voltage is increased, the intensity of the X-rays increases without changing its frequency and hence increases its penetrating power. The high intensity spikes are characteristics of the target material. The anode is cooled to dissipate the heat produced.
Since X-rays are emitted in all directions, the tube is enclosed in a lead case with a small window to provide an outlet for the X-ray beam. A photograph of X-ray table is shown below:
From the figure above, you can see that, the patient is made to lie on the X-ray table. A photographic plate is placed beneath the area under examination. The X-ray beam is directed on the area. From the control panel, the technician or radiologist can control the timing and the frequency of the rays.
You can also read: The Introduction to Biomedical Instrumentation
X-rays are used for:
You can also read: The Introduction to Medical Diagnostics Techniques
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It's nice that you talked about how a major application of X-rays is in angiography, to study blockages of blood vessels. I was watching a health program the other day and it talked about the usefulness of X-rays. According to what I've learned, it seems there are various X-ray services available now too, like nursing home X-ray services.
Hi Luke, glad to know that.