The principle and structure of the X-ray machine 1895 German physicist R?ntgen (W. C. R& Ouml;ntgen) in the study of cathode ray tube in the gas discharge phenomenon, with a embedded two metal electrodes (one is called the anode, one is called the cathode) of the sealed glass tube, the electrodes at the ends of the high-voltage electricity plus several tens of thousands of volts, with the pumping machine from the glass tube out of the air. In order to block the leakage of light (a kind of arc light) from the high-voltage discharge, a layer of black cardboard was placed over the glass tube. While conducting this experiment in a dark room, he happened to notice that two meters away from the glass tube, a piece of cardboard washed with a solution of barium platinum cyanide emitted bright fluorescence. Further tests with cardboard, boards, clothes and books about two thousand pages thick could not block this fluorescence. Even more surprisingly, when the fluorescent cardboard was held in the hand, the image of a hand bone was seen on the cardboard.
R?ntgen concluded that this was a kind of ray that was invisible to the human eye but could penetrate objects. Unable to explain its principle, unknown its nature, it borrowed the mathematical representation of the unknown number of "X" as a code name, known as "X" rays (or X-rays or X-ray for short). This is the discovery of X-rays and the origin of the name. This name has been used to this day. In honor of Roentgen's great discovery, it was named Roentgen rays.
The discovery of X-rays is of great significance in the history of mankind, and it opened a new path for natural science and medicine, for which R?ntgen was honored with the first Nobel Prize in physics in 1901.
Science is always in constant development, by R?ntgen and the repeated practice and research of scientists from all over the world, gradually revealing the nature of X-rays, confirming that it is a very short wavelength, a great deal of energy electromagnetic waves. Its wavelength is shorter than the wavelength of visible light (about 0.001 ~ 100nm, medical applications of X-rays wavelength of about 0.001. ~ 0.1nm), and its photon energy than the photon energy of visible light several tens of thousands to hundreds of thousands of times. Therefore, X-rays in addition to the general nature of visible light, but also has its own characteristics. (A) physical effects
1. penetration effect penetration effect refers to the X-rays through the material is not absorbed when the ability to X-rays can penetrate the general visible light can not be through the material. Visible light because of its long wavelength, photons of its energy is very small, when shot to the object, part of the reflection, most of the material is absorbed, can not pass through the object; X-rays is not, because of its short wavelength, energy, shine on the material, only part of the material is absorbed, most of the interatomic space and through the performance of a very strong ability to penetrate the X-rays penetrate the material and X-ray photon energy related to the wavelength of X-rays, X-rays are not absorbed, but can not be absorbed. The ability of X-rays to penetrate matter and the energy of X-ray photons, the shorter the wavelength of the X-rays, the greater the energy of the photons, the stronger the penetration of X-rays, X-rays penetration is also related to the density of the material, the density of the material, X-rays absorbed more through less; density of small, less absorbed, through more. The use of differential absorption of this nature can be different density of bone, muscle, fat and other soft tissues can be distinguished. This is the physical basis of X-ray fluoroscopy and photography.
2. Ionization of matter by X-ray irradiation, so that the nuclear electrons out of the atomic orbitals, this effect is called ionization. In the photoelectric effect and scattering process, the emergence of photoelectrons and recoil electrons from its atomic process called primary ionization, these photoelectrons or recoil electrons in the travel and other atomic collisions, so that the struck atoms escape electrons called secondary ionization. In solids and liquids. Ionized positive and negative ions will be quickly compounded, not easy to collect. But in the gas in the forget ionized charge is very easy to collect, the use of ionized charge how much can be determined by the amount of X-ray exposure: X-ray measuring instrument is made according to this principle. As a result of ionization, gases can conduct electricity; certain substances can undergo chemical reactions; and various biological effects can be induced in organisms. Ionization is the basis of X-ray damage and treatment.
3. Fluorescence Due to the short wavelength of X-rays, it is invisible. But it irradiated to some compounds such as phosphorus, platinum barium cyanide, zinc cadmium sulfide, calcium tungstate, etc., due to ionization or excitation of atoms in the excited state, the atom back to the base state process, due to the valence electrons of the energy level of the leap and radiate visible light or ultraviolet light, which is fluorescence. x-rays to make the material fluorescence is called fluorescence. The intensity of fluorescence is proportional to the amount of X-rays. This effect is the basis for the use of X-rays in fluoroscopy. In X-ray diagnostic work using this fluorescence effect can be made into a fluorescent screen, sensing screen, image intensifier in the input screen and so on. Fluorescent screen used for fluoroscopy to observe X-rays through the human body tissue image, the screen is used as a photographic enhancement of the film's sensitivity.
4. Thermal effect of the X-ray energy absorbed by the material, most of which is converted into heat, so that the temperature of the object increases, which is the thermal effect.
5. Interference, diffraction, reflection, refraction These effects are the same as visible light. In X-ray microscopy, wavelength determination and material structure analysis are applied.
(B) chemical effects
1. photographic effect with visible light, X-rays can make the film photographic. When X-rays irradiated to the film on the silver bromide, can make silver particles. Precipitation and make the film to produce "photographic effect". The strength of the film's sensitivity is directly proportional to the amount of X-rays. When X-rays through the human body, because of the density of the human body tissues are different, the amount of X-rays absorbed by different, resulting in the bloom of the film on the sensitivity of the different, so as to obtain the image of X-rays. This is the basis of the application of X-rays for film examination.
2. coloring effect of certain substances such as platinum barium cyanide, lead glass, crystal, etc., after long-term irradiation of X-rays, its crystals dehydrated and change color, which is called coloring effect.
(C) biological effects'
When X-rays irradiated to the biological organism, biological cells are inhibited, destroyed or even necrosis, resulting in different degrees of physiological, pathological and biochemical changes in the organism, known as the biological effects of X-rays. Different biological cells have different sensitivity to X-rays. Maple X-rays can treat certain diseases in the human body, such as tumors. On the other hand, it is also harmful to the normal organism, so it is necessary to do a good job of protection of the human body.The biological effects of X-rays are ultimately caused by the ionization of X-rays. As X-rays have all the above effects! Therefore, in industry, agriculture, scientific research and other fields, access to a wide range of applications, such as industrial injury detection, crystal analysis. In medicine, X-ray technology has become a specialized discipline for the diagnosis and treatment of diseases, and occupies an important position in health care. (A) X-ray diagnosis
X-ray applied to medical diagnosis, mainly based on the X-ray penetration, differential absorption, photosensitivity and fluorescence. As X-rays through the human body, by different degrees of absorption, such as the amount of X-rays absorbed by the bone than the amount absorbed by the muscle, then the amount of X-rays through the human body is not the same, so that it carries the density distribution of the human body parts of the information in the fluorescence screen or photographic film caused by fluorescence or photographic effect of the strength of the role of a greater difference, and therefore in the fluorescent screen or photographic film (after developing, fixing ) will show a different density of shadows. According to the contrast of shadow intensity, combined with clinical manifestations, laboratory results and pathological diagnosis, it can be judged whether a certain part of the human body is normal or not. Thus, X-ray diagnostic technology has become the world's first application of non-invasive visceral examination technology.
(2) X-ray therapy
X-ray therapy, mainly based on its biological effects, the application of different energy X-ray irradiation of the human body foci part of the cellular tissues, can be irradiated cellular tissues are destroyed or inhibited, so as to achieve the treatment of certain diseases, especially the purpose of the treatment of tumors.
(C) X-ray protection
In the use of X-rays at the same time, people have found to lead to patients with hair loss, skin burns, staff visual impairment, leukemia and other radiation damage, in order to prevent X-rays on the human body, must take appropriate protective measures. The above constitutes the three major aspects of X-ray application in medicine - diagnosis, treatment and protection. Since 1895, X-ray diagnostic and therapeutic technology has developed rapidly, the main progress can be divided into the following stages:
(a) Ion X-ray tube stage (1895 ~ 1912)
This is the early stage of X-ray equipment. At that time, the structure of the X-ray machine is very simple, the use of very low-efficiency gas-containing cold cathode ion X-ray tube, the use of bulky induction coils to generate high pressure, exposed high-voltage components, not to mention the precise control device. X-ray machine device capacity is small, low efficiency, penetration is weak, the image clarity is not high, the lack of protection 0 According to the data recorded at the time of the shooting of an X-ray pelvic image, need to be as long as 40 to 60min According to the data, it took 40 to 60min of exposure time to take an X-ray image of the pelvis, and as a result, the subject's skin was burned by the X-rays after the photo was taken.
(II) electronic X-ray tube stage (1913 ~ 1928)
With the development of electromagnetism, high-vacuum technology and other disciplines, in 1910, the American physicist W. D. Coolidge published a report on the success of the manufacture of tungsten filament X-ray tubes. 1913 began to be used in practice, and its most important feature is that the * tungsten filament is heated to incandescence to provide the electrons required for the tube current. The most important feature is that the tungsten filament is heated to incandescent state to provide the electrons needed for the tube current, so the heating temperature of the filament can be adjusted to control the tube current, so that the tube voltage and the tube current can be adjusted independently of each other, which is exactly what is needed to improve the quality of the image.
In 1913, the invention of filter grids, partially eliminating scattered rays, improving the quality of the image. 1914 made cadmium tungstate fluorescent screen, the beginning of the application of X-ray fluoroscopy. 1923 invented the dual-focus X-ray tube, to solve the need for X-ray radiography, the power of the tube can be up to a few kilowatts, the rectangular focal length of the side of only a few millimeters, the quality of the X-ray image is greatly improved. The quality of X-ray images was greatly improved. At the same time, the gradual application of contrast agents has expanded the diagnostic scope of X-rays. It is no longer a simple tool to simply shoot bone images, but has become an important medical diagnostic facility for human tissues and organs that have poor natural contrast (small absorption of X-rays) of the gastrointestinal tract, bronchial tubes, blood vessels, ventricles, kidneys, bladders and other important medical diagnostic facilities can be examined. At the same time, X-rays are beginning to be used in therapy.
X-ray generation
Three ways can produce X-ray: bremsstrahlung (Bremsstrahlung), electron capture, internal conversion, x-ray machine to produce X-ray mechanism belongs to bremsstrahlung.
Electron capture:
Beta decay consists of three ways: beta-decay, beta+decay and electron capture (EC). The electron capture (EC) decay can be expressed as follows: the mother nucleus captures one electron in an extra-nuclear orbital so that one proton in the nucleus is transformed into a neutron and one neutrino is emitted, so that the charge of the daughter nucleus is changed to Z-1, while the mass number remains unchanged. In general, most electrons on the K layer are captured by the nucleus because the K layer is closest to the nucleus and has the highest probability of capture, but there is also a probability that electrons on the L layer are captured. After the nucleus has captured an electron, there will be an electron vacancy in the K or L layer of the nucleus, and when one of the outer electrons fills the vacancy, one of two things may happen: either the excess energy is released in the form of a marker X-ray, or the excess energy is given to another electron in another layer, which gains energy and breaks away from the atom as an Rochelle electron. The emission of X-rays or Rochelle electrons is the hallmark of the K-capture process.
Internal transition:
The nucleus of an atom can reach an excited state in some way (e.g., beta decay), and the nucleus in the excited state can jump to a lower excited state or to the ground state by emitting gamma rays, a phenomenon known as gamma decay or gamma jump. The photons emitted by nuclear level leaps are not fundamentally different from those emitted by atomic level leaps, except that the photon energy emitted by atomic level leaps is only of the order of eV~keV, while the photon energy emitted by nuclear level leaps is of the order of MeV. In the nuclear recoil is not taken into account, the photon energy Eg can be expressed as the following form Eg = Es-Ex. Sometimes the atomic nucleus from the excited state to the lower energy state of the leap does not release photons, but the energy directly to the nuclear electrons, so that the electrons out of the atom, a phenomenon known as internal conversion (IC), out of the atom of the electrons known as the internal conversion of the electrons. In the excited state of the nucleus can be radiated γ photons back to the ground state, but also through the production of internal conversion electrons back to the ground state, which process occurs, is entirely dependent on the energy level of the nuclear properties. The sum of the kinetic energy of the internal conversion electrons and the ionization energy of the shell electrons should be the energy difference between the two energy levels of the nucleus. That is, it is equal to the energy of the gamma photon radiated by the jump between the energy levels of the two nuclei. The study of internal transitions is an important means of obtaining knowledge about the energy levels of the nucleus. Of course, it is also possible to produce the characteristic X-rays of an atom by means of internal transitions.
Fundamentals of the x-ray machine
The X-ray was discovered by Prof. Luncheon in Germany in 1895. This kind of radiation emitted by the vacuum tube can penetrate the object, in the electromagnetic spectrum of energy is stronger than visible light, shorter wavelength, higher frequency, similar to the radiation ray cosmic rays, X-ray and so on.
To produce X-Ray, you must have an X-ray dome, and the basic structure of the X-ray dome must have:
Cathode filament (Cathod)
Anode target (Anode)
Vacuated glass envelope (Evacuated glass envelope)
Of course, there must also be a power supply energy
The X-ray dome can be used to produce X-Ray, but it can be used to produce X-Ray.
X-ray properties
Penetrates objects, is invisible, is in the electromagnetic spectrum, has a wide range of wavelengths, scatters in a straight line, and travels at the speed of light, can emit light from fluorescent materials, can sensitize film, and can cause scattering
When X-ray enters an object, there are three ways in which it can be absorbed
Scattered by the object
Scattered by the object
Scattered by the object
Scattering of X-rays by the object
The X-rays can be scattered into an object. （Scatter
Penetration
Four elements that affect the image:
Density - mAs
Contrast - kVp
Sharpness - motion, a geometric parameter
Distortion - a parameter that is used to measure the contrast of the image.
Distortion - position, angle
Relation between X-ray wavelength and contrast on film
In X-ray penetration through the patient, the penetration rate is mainly related to the patient's tissue structure and the wavelength of X-rays.
Short-wavelength X-rays (high kV)
have higher energy and better penetration, resulting in lower contrast on the film.
Long-wavelength X-ray (low kV)
Lower energy, easier to be absorbed by the human body, less penetrating, resulting in higher contrast in the movie.
Applications
The X-ray machine is widely used in health care, science and education, and industry, for example, X-ray machines can be used in hospitals to assist doctors in diagnosing diseases, for non-destructive testing in industry, and for security inspections in train stations and airports, and so on.