photoelectric effect

hv ³ A and

photon is absorbed, e - detached from the atom - ionization

hv \u003d A and + E to

atom A excited by the absorption of a photon, R – X-ray luminescence

incoherent scattering

hv » A and

hv \u003d hv "+ A and + E to

secondary processes in the photoelectric effect

Rice. 3 Mechanisms of interaction of X-rays with matter

Physical basis for the use of X-rays in medicine

When X-rays fall on a body, it is slightly reflected from its surface, but mainly passes deep into, while it is partially absorbed and scattered, and partially passes through.

The law of weakening.

The X-ray flux is attenuated in matter according to the law:

F \u003d F 0 e - m × x (6)

where m – linear attenuation factor, which essentially depends on the density of the substance. He is equal to the sum three terms corresponding to coherent scattering m 1, incoherent m 2 and photoelectric effect m 3:

m \u003d m 1 + m 2 + m 3. (7)

The contribution of each term is determined by the photon energy. Below are the ratios of these processes for soft tissues (water).

enjoy mass attenuation coefficient, which does not depend on the density of the substance r :

m m = m / r . (eight)

The mass attenuation coefficient depends on the energy of the photon and on the atomic number of the absorbing substance:

m m = k l 3 Z 3 . (9)

Mass attenuation coefficients of bone and soft tissue (water) differ: m m bones / m m water = 68.

If an inhomogeneous body is placed in the path of X-rays and a fluorescent screen is placed in front of it, then this body, absorbing and attenuating the radiation, forms a shadow on the screen. By the nature of this shadow, one can judge the shape, density, structure, and in many cases the nature of bodies. Those. a significant difference in the absorption of x-ray radiation by different tissues allows you to see the image of the internal organs in the shadow projection.

If the organ under study and the surrounding tissues equally attenuate x-rays, then contrast agents are used. So, for example, filling the stomach and intestines with a mushy mass of barium sulfate ( BaS 0 4), you can see their shadow image (the ratio of attenuation coefficients is 354).

Use in medicine.

In medicine, X-ray radiation with photon energy from 60 to 100-120 keV is used for diagnostics and 150-200 keV for therapy.

X-ray diagnostics – Recognition of diseases by transilluminating the body with X-rays.

Radiodiagnosis is used in various options which are listed below.

1. With fluoroscopy the x-ray tube is located behind the patient. In front of it is a fluorescent screen. There is a shadow (positive) image on the screen. In each individual case, the appropriate hardness of the radiation is selected so that it passes through soft tissues, but is sufficiently absorbed by dense ones. Otherwise, a uniform shadow is obtained. On the screen, the heart, the ribs are visible dark, the lungs are light.

2. When radiography the object is placed on a cassette, which contains a film with a special photographic emulsion. The X-ray tube is placed over the object. The resulting radiograph gives a negative image, i.e. the opposite in contrast to the picture observed during transillumination. In this method, there is a greater clarity of the image than in (1), therefore, details are observed that are difficult to see when transilluminated.

A promising variant of this method is X-ray tomography and "machine version" - computer tomography.

3. With fluoroscopy, On a sensitive small-format film, the image from the large screen is fixed. When viewed, the pictures are examined on a special magnifier.

X-ray therapy - the use of X-rays to destroy malignant tumors.

The biological effect of radiation is to disrupt vital activity, especially rapidly multiplying cells.

COMPUTED TOMOGRAPHY (CT)

The method of X-ray computed tomography is based on image reconstructiondefined section of the patient's body by registering a large number X-ray projections of this section, made at different angles. Information from the sensors that register these projections enters the computer, which special program calculates distribution tightly sample sizein the investigated section and displays it on the display screen. The resulting imagesection of the patient's body is characterized by excellent clarity and high information content. The program allows you toincrease image contrast in dozens and even hundreds of times. This expands the diagnostic capabilities of the method.

Videographers (devices with digital X-ray image processing) in modern dentistry.

In dentistry it x-ray examination is the main diagnostic method. However, a number of traditional organizational and technical features of X-ray diagnostics make it not quite comfortable for both the patient and dental clinics. This is, first of all, the need for the patient to come into contact with ionizing radiation, which often creates a significant radiation load on the body, it is also the need for a photoprocess, and, consequently, the need for photoreagents, including toxic ones. This is, finally, a bulky archive, heavy folders and envelopes with x-ray films.

In addition, the current level of development of dentistry makes the subjective assessment of radiographs by the human eye insufficient. As it turned out, of the variety of shades of gray contained in the x-ray image, the eye perceives only 64.

Obviously, to obtain a clear and detailed image of the hard tissues of the dentoalveolar system with minimal radiation exposure, other solutions are needed. The search led to the creation of so-called radiographic systems, videographers - digital radiography systems.

Without technical details, the principle of operation of such systems is as follows. X-ray radiation enters through the object not on a photosensitive film, but on a special intraoral sensor (special electronic matrix). The corresponding signal from the matrix is ​​transmitted to a digitizing device (analog-to-digital converter, ADC) that converts it into digital form and is connected to the computer. Special software builds an x-ray image on the computer screen and allows you to process it, save it on a hard or flexible storage medium (hard drive, floppy disks), print it as a picture as a file.

In a digital system, an x-ray image is a collection of dots having different digital grayscale values. The information display optimization provided by the program makes it possible to obtain an optimal frame in terms of brightness and contrast at a relatively low radiation dose.

In modern systems created, for example, by firms Trophy (France) or Schick (USA) when forming a frame, 4096 shades of gray are used, the exposure time depends on the object of study and, on average, is hundredths - tenths of a second, reduction of radiation exposure in relation to the film - up to 90% for intraoral systems, up to 70% for panoramic videographers.

When processing images, videographers allow:

1. Get positive and negative images, false color images, embossed images.

2. Increase contrast and magnify the area of ​​interest in the image.

3. Assess changes in the density of dental tissues and bone structures, control the uniformity of canal filling.

4. In endodontics to determine the length of the channel of any curvature, and in surgery to select the size of the implant with an accuracy of 0.1 mm.

5. Unique system caries detector with elements artificial intelligence when analyzing the image, it allows you to detect caries in the stain stage, root caries and hidden caries.

* « Ф" in formula (3) refers to the entire range of emitted wavelengths and is often referred to as "Integral Energy Flux".

LECTURE

X-RAY RADIATION

The nature of X-rays

Bremsstrahlung X-ray, its spectral properties.

Characteristic x-ray radiation (for review).

Interaction of X-ray radiation with matter.

Physical basis for the use of X-rays in medicine.

X-rays (X - rays) were discovered by K. Roentgen, who in 1895 became the first Nobel laureate in physics.

The nature of X-rays

x-ray radiation - electromagnetic waves with a length of 80 to 10 -5 nm. Long-wave X-ray radiation is covered by short-wave UV radiation, and short-wave radiation by long-wave  radiation.

X-rays are produced in x-ray tubes. fig.1.

K - cathode

1 - electron beam

2 - X-ray radiation

Rice. 1. X-ray tube device.

The tube is a glass flask (with a possibly high vacuum: the pressure in it is about 10–6 mm Hg) with two electrodes: the anode A and the cathode K, to which a high voltage U (several thousand volts) is applied. The cathode is a source of electrons (due to the phenomenon of thermionic emission). The anode is a metal rod that has an inclined surface in order to direct the resulting X-ray radiation at an angle to the axis of the tube. It is made of a highly heat-conducting material to remove the heat generated during electron bombardment. On the beveled end there is a plate made of refractory metal (for example, tungsten).

The strong heating of the anode is due to the fact that the main number of electrons in the cathode beam, having hit the anode, experience numerous collisions with the atoms of the substance and transfer a large amount of energy to them.

Under the action of high voltage, the electrons emitted by the hot cathode filament are accelerated to high energies. The kinetic energy of an electron is equal to mv 2 /2. It is equal to the energy that it acquires by moving in the electrostatic field of the tube:

mv 2 /2 = eU(1)

where m, e are the electron mass and charge, U is the accelerating voltage.

The processes leading to the appearance of bremsstrahlung X-rays are due to the intense deceleration of electrons in the anode material by the electrostatic field of the atomic nucleus and atomic electrons.

The origin mechanism can be represented as follows. Moving electrons are some kind of current that forms its own magnetic field. Electron deceleration is a decrease in the current strength and, accordingly, a change in the magnetic field induction, which will cause the appearance of an alternating electric field, i.e. appearance of an electromagnetic wave.

Thus, when a charged particle flies into matter, it slows down, loses its energy and speed, and emits electromagnetic waves.

Spectral properties of X-ray bremsstrahlung .

So, in the case of electron deceleration in the anode material, bremsstrahlung radiation.

The bremsstrahlung spectrum is continuous. The reason for this is as follows.

When electrons decelerate, each of them has part of the energy used to heat the anode (E 1 \u003d Q), the other part to create an X-ray photon (E 2 \u003d hv), otherwise, eU \u003d hv + Q. The ratio between these parts is random.

Thus, the continuous spectrum of X-ray bremsstrahlung is formed due to the deceleration of many electrons, each of which emits one X-ray quantum hv (h) of a strictly defined value. The value of this quantum different for different electrons. Dependence of the X-ray energy flux on the wavelength , i.e. the X-ray spectrum is shown in Fig.2.

Fig.2. Bremsstrahlung spectrum: a) at different voltages U in the tube; b) at different temperatures T of the cathode.

Short-wave (hard) radiation has a greater penetrating power than long-wave (soft) radiation. Soft radiation is more strongly absorbed by matter.

From the side of short wavelengths, the spectrum ends abruptly at a certain wavelength  m i n . Such short-wavelength bremsstrahlung occurs when the energy acquired by an electron in an accelerating field is completely converted into photon energy (Q = 0):

eU = hv max = hc/ min ,  min = hc/(eU), (2)

 min (nm) = 1.23/UkV

The spectral composition of the radiation depends on the voltage on the X-ray tube; with increasing voltage, the value of  m i n shifts towards short wavelengths (Fig. 2a).

When the temperature T of the cathode incandescence changes, the electron emission increases. Consequently, the current I in the tube increases, but the spectral composition of the radiation does not change (Fig. 2b).

The energy flux Ф  of bremsstrahlung is directly proportional to the square of the voltage U between the anode and the cathode, the current strength I in the tube, and the atomic number Z of the anode substance:

Ф = kZU 2 I. (3)

where k \u003d 10 -9 W / (V 2 A).

Characteristic X-rays (for familiarization).

Increasing the voltage on the X-ray tube leads to the fact that against the background of a continuous spectrum, a line appears, which corresponds to the characteristic X-ray radiation. This radiation is specific to the anode material.

The mechanism of its occurrence is as follows. At a high voltage, accelerated electrons (with high energy) penetrate deep into the atom and knock electrons out of its inner layers. Electrons from upper levels pass to free places, as a result of which photons of characteristic radiation are emitted.

The spectra of characteristic X-rays differ from optical spectra.

- Uniformity.

The uniformity of the characteristic spectra is due to the fact that the internal electron layers of different atoms are the same and differ only energetically due to the force action from the nuclei, which increases with increasing elemental number. Therefore, the characteristic spectra shift towards higher frequencies with increasing nuclear charge. This was experimentally confirmed by an employee of Roentgen - Moseley, who measured X-ray transition frequencies for 33 elements. They made the law.

MOSELY'S LAW – the square root of the frequency of the characteristic radiation is a linear function of the ordinal number of the element:

= A  (Z - B), (4)

where v is the frequency of the spectral line, Z is the atomic number of the emitting element. A, B are constants.

The importance of Moseley's law lies in the fact that this dependence can be used to accurately determine the atomic number of the element under study from the measured frequency of the X-ray line. This played a big role in the placement of the elements in the periodic table.

Independence from a chemical compound.

The characteristic X-ray spectra of an atom do not depend on the chemical compound in which the atom of the element enters. For example, the X-ray spectrum of an oxygen atom is the same for O 2, H 2 O, while the optical spectra of these compounds differ. This feature of the x-ray spectrum of the atom was the basis for the name " characteristic radiation".

Interaction of X-ray radiation with matter

The impact of X-ray radiation on objects is determined by the primary processes of X-ray interaction. photon with electrons atoms and molecules of matter.

X-ray radiation in matter absorbed or dissipates. In this case, various processes can occur, which are determined by the ratio of the X-ray photon energy hv and the ionization energy Аu (ionization energy Аu is the energy required to remove internal electrons from the atom or molecule).

a) Coherent scattering(scattering of long-wave radiation) occurs when the relation

For photons, due to interaction with electrons, only the direction of movement changes (Fig. 3a), but the energy hv and the wavelength do not change (therefore, this scattering is called coherent). Since the energies of a photon and an atom do not change, coherent scattering does not affect biological objects, but when creating protection against X-ray radiation, one should take into account the possibility of changing the primary direction of the beam.

b) photoelectric effect happens when

In this case, two cases can be realized.

The photon is absorbed, the electron is detached from the atom (Fig. 3b). Ionization occurs. The detached electron acquires kinetic energy: E k \u003d hv - A and. If the kinetic energy is large, then the electron can ionize neighboring atoms by collision, forming new ones. secondary electrons.

The photon is absorbed, but its energy is not enough to detach the electron, and excitation of an atom or molecule(Fig. 3c). This often leads to the subsequent emission of a photon in the visible radiation region (X-ray luminescence), and in tissues - to the activation of molecules and photochemical reactions. The photoelectric effect occurs mainly on the electrons of the inner shells of atoms with high Z.

in) Incoherent scattering(Compton effect, 1922) occurs when the photon energy is much greater than the ionization energy

In this case, the electron is detached from the atom (such electrons are called recoil electrons), acquires some kinetic energy E k, the energy of the photon itself decreases (Fig. 4d):

hv=hv" + A and + E k. (5)

The resulting radiation with a changed frequency (length) is called secondary, it scatters in all directions.

Recoil electrons, if they have sufficient kinetic energy, can ionize neighboring atoms by collision. Thus, as a result of incoherent scattering, secondary scattered X-ray radiation is formed and the atoms of the substance are ionized.

These (a, b, c) processes can cause a number of subsequent ones. For example (Fig. 3d), if during the photoelectric effect electrons are detached from the atom on the inner shells, then electrons from higher levels can pass in their place, which is accompanied by secondary characteristic x-ray radiation of this substance. Photons of secondary radiation, interacting with electrons of neighboring atoms, can, in turn, cause secondary phenomena.

coherent scattering

uh energy and wavelength remain unchanged

photoelectric effect

photon is absorbed, e - detached from the atom - ionization

hv \u003d A and + E to

atom A is excited upon absorption of a photon, R is X-ray luminescence

incoherent scattering

hv \u003d hv "+ A and + E to

secondary processes in the photoelectric effect

Rice. 3 Mechanisms of X-ray interaction with matter

Physical basis for the use of X-rays in medicine

When X-rays fall on a body, it is slightly reflected from its surface, but mainly passes deep into, while it is partially absorbed and scattered, and partially passes through.

The law of weakening.

The X-ray flux is attenuated in matter according to the law:

F \u003d F 0 e -   x (6)

where  is linear attenuation factor, which essentially depends on the density of the substance. It is equal to the sum of three terms corresponding to coherent scattering  1, incoherent  2 and photoelectric effect  3:

 =  1 +  2 +  3 . (7)

The contribution of each term is determined by the photon energy. Below are the ratios of these processes for soft tissues (water).

enjoy mass attenuation coefficient, which does not depend on the density of the substance :

m = /. (eight)

The mass attenuation coefficient depends on the energy of the photon and on the atomic number of the absorbing substance:

 m = k 3 Z 3 . (9)

The mass attenuation coefficients of bone and soft tissue (water) are different:  m bone /  m water = 68.

If an inhomogeneous body is placed in the path of X-rays and a fluorescent screen is placed in front of it, then this body, absorbing and attenuating the radiation, forms a shadow on the screen. By the nature of this shadow, one can judge the shape, density, structure, and in many cases the nature of bodies. Those. a significant difference in the absorption of x-ray radiation by different tissues allows you to see the image of the internal organs in the shadow projection.

If the organ under study and the surrounding tissues equally attenuate x-rays, then contrast agents are used. So, for example, filling the stomach and intestines with a mushy mass of barium sulfate (BaSO 4 ), one can see their shadow image (the ratio of the attenuation coefficients is 354).

Use in medicine.

In medicine, X-ray radiation with photon energy from 60 to 100-120 keV is used for diagnostics and 150-200 keV for therapy.

X-ray diagnostics – Recognition of diseases by transilluminating the body with X-rays.

X-ray diagnostics is used in various options, which are given below.

With fluoroscopy the x-ray tube is located behind the patient. In front of it is a fluorescent screen. There is a shadow (positive) image on the screen. In each individual case, the appropriate hardness of the radiation is selected so that it passes through soft tissues, but is sufficiently absorbed by dense ones. Otherwise, a uniform shadow is obtained. On the screen, the heart, the ribs are visible dark, the lungs are light.

When radiography the object is placed on a cassette, which contains a film with a special photographic emulsion. The X-ray tube is placed over the object. The resulting radiograph gives a negative image, i.e. the opposite in contrast to the picture observed during transillumination. In this method, there is a greater clarity of the image than in (1), therefore, details are observed that are difficult to see when transilluminated.

A promising variant of this method is X-ray tomography and "machine version" - computer tomography.

3. With fluoroscopy, On a sensitive small-format film, the image from the large screen is fixed. When viewed, the pictures are examined on a special magnifier.

X-ray therapy- the use of X-rays to destroy malignant tumors.

The biological effect of radiation is to disrupt vital activity, especially rapidly multiplying cells.

COMPUTED TOMOGRAPHY (CT)

The method of X-ray computed tomography is based on the reconstruction of an image of a certain section of the patient's body by registering a large number of X-ray projections of this section, made at different angles. Information from the sensors that register these projections enters the computer, which, according to a special program calculates distribution tightlysample size in the investigated section and displays it on the display screen. The image of the section of the patient's body obtained in this way is characterized by excellent clarity and high information content. The program allows you to increase image contrast in dozens and even hundreds of times. This expands the diagnostic capabilities of the method.

Videographers (devices with digital X-ray image processing) in modern dentistry.

In dentistry, X-ray examination is the main diagnostic method. However, a number of traditional organizational and technical features of X-ray diagnostics make it not quite comfortable for both the patient and dental clinics. This is, first of all, the need for the patient to come into contact with ionizing radiation, which often creates a significant radiation load on the body, it is also the need for a photoprocess, and, consequently, the need for photoreagents, including toxic ones. This is, finally, a bulky archive, heavy folders and envelopes with x-ray films.

In addition, the current level of development of dentistry makes the subjective assessment of radiographs by the human eye insufficient. As it turned out, of the variety of shades of gray contained in the x-ray image, the eye perceives only 64.

Obviously, to obtain a clear and detailed image of the hard tissues of the dentoalveolar system with minimal radiation exposure, other solutions are needed. The search led to the creation of so-called radiographic systems, videographers - digital radiography systems.

Without technical details, the principle of operation of such systems is as follows. X-ray radiation enters through the object not on a photosensitive film, but on a special intraoral sensor (special electronic matrix). The corresponding signal from the matrix is ​​transmitted to a digitizing device (analog-to-digital converter, ADC) that converts it into digital form and is connected to the computer. Special software builds an x-ray image on the computer screen and allows you to process it, save it on a hard or flexible storage medium (hard drive, floppy disks), print it as a picture as a file.

In a digital system, an x-ray image is a collection of dots having different digital grayscale values. The information display optimization provided by the program makes it possible to obtain an optimal frame in terms of brightness and contrast at a relatively low radiation dose.

In modern systems, created, for example, by Trophy (France) or Schick (USA), 4096 shades of gray are used when forming a frame, the exposure time depends on the object of study and, on average, is hundredths - tenths of a second, a decrease in radiation exposure in relation to film - up to 90% for intraoral systems, up to 70% for panoramic videographers.

When processing images, videographers allow:

Get positive and negative images, false color images, embossed images.

Increase contrast and magnify the area of ​​interest in the image.

Assess changes in the density of dental tissues and bone structures, control the uniformity of canal filling.

In endodontics, determine the length of the canal of any curvature, and in surgery, select the size of the implant with an accuracy of 0.1 mm.

The unique Caries detector system with elements of artificial intelligence during the analysis of the image allows you to detect caries in the stain stage, root caries and hidden caries.

"F" in formula (3) refers to the entire range of radiated wavelengths and is often referred to as "Integral Energy Flux".

X-ray radiation plays a huge role in modern medicine; the history of the discovery of X-rays dates back to the 19th century.

X-rays are electromagnetic waves that are produced with the participation of electrons. With strong acceleration of charged particles, artificial x-rays are created. It passes through special equipment:

• particle accelerators.

Discovery history

These rays were invented in 1895 by the German scientist Roentgen: while working with a cathode ray tube, he discovered the fluorescence effect of barium platinum cyanide. Then there was a description of such rays and their amazing ability to penetrate the tissues of the body. The rays began to be called x-rays (x-rays). Later in Russia they began to be called X-ray.

X-rays are able to penetrate even through walls. So Roentgen realized what he had done greatest discovery in medecine. It was from that time that separate sections in science began to form, such as radiology and radiology.

The rays are able to penetrate soft tissues, but are delayed, their length is determined by the obstacle of a hard surface. The soft tissues in the human body are the skin, and the hard tissues are the bones. In 1901, the scientist was awarded Nobel Prize.

However, even before the discovery of Wilhelm Conrad Roentgen, other scientists were also interested in a similar topic. In 1853, the French physicist Antoine-Philiber Mason studied a high-voltage discharge between electrodes in a glass tube. The gas contained in it at low pressure began to emit a reddish glow. Pumping out excess gas from the tube led to the decay of the glow into a complex sequence of individual luminous layers, the hue of which depended on the amount of gas.

In 1878, William Crookes (English physicist) suggested that fluorescence occurs due to the impact of rays on the glass surface of the tube. But all these studies were not published anywhere, so Roentgen did not know about such discoveries. After the publication of his discoveries in 1895 in scientific journal, where the scientist wrote that all bodies are transparent to these rays, although to a very different degree, other scientists became interested in similar experiments. They confirmed the invention of Roentgen, and further development and improvement of x-rays began.

Wilhelm Roentgen himself published two more scientific work on the subject of x-rays in 1896 and 1897, after which he took up other activities. Thus, several scientists invented, but it was Roentgen who published scientific works on this occasion.

Imaging Principles

The features of this radiation are determined by the very nature of their appearance. Radiation occurs due to an electromagnetic wave. Its main properties include:

1. Reflection. If the wave hits the surface perpendicularly, it will not be reflected. In some situations, a diamond has the property of reflection.
2. The ability to penetrate tissue. In addition, the rays can pass through opaque surfaces of materials such as wood, paper, and the like.
3. absorbency. Absorption depends on the density of the material: the denser it is, the more X-rays absorb it.
4. Some substances fluoresce, that is, they glow. As soon as the radiation stops, the glow also disappears. If it continues after the cessation of the action of the rays, then this effect is called phosphorescence.
5. X-rays can illuminate photographic film, just like visible light.
6. If the beam passed through the air, then ionization occurs in the atmosphere. This state is called electrically conductive, and it is determined using a dosimeter, which sets the rate of radiation dosage.

Radiation - harm and benefit

When the discovery was made, the physicist Roentgen could not even imagine how dangerous his invention was. In the old days, all devices that produced radiation were far from perfect, and as a result, large doses of emitted rays were obtained. People did not understand the dangers of such radiation. Although some scientists even then put forward versions about the dangers of x-rays.

X-rays, penetrating into tissues, have a biological effect on them. The unit of measurement of radiation dose is roentgen per hour. The main influence is on the ionizing atoms that are inside the tissues. These rays act directly on the DNA structure of a living cell. The consequences of uncontrolled radiation include:

• cell mutation;
• the appearance of tumors;
• radiation burns;
• radiation sickness.

Contraindications for X-ray examinations:

1. The patients are in critical condition.
2. Pregnancy period due to negative effects on the fetus.
3. Patients with bleeding or open pneumothorax.

How x-rays work and where it is used

1. In medicine. X-ray diagnostics is used to translucent living tissues in order to identify certain disorders within the body. X-ray therapy is performed to eliminate tumor formations.
2. In science. The structure of substances and the nature of X-rays are revealed. These issues are dealt with by such sciences as chemistry, biochemistry, crystallography.
3. In industry. To detect violations in metal products.
4. For the safety of the population. X-ray beams are installed at airports and other in public places for the purpose of screening luggage.

Medical use of X-ray radiation. X-rays are widely used in medicine and dentistry. following purposes:

1. For diagnosing diseases.
2. For monitoring metabolic processes.
3. For the treatment of many diseases.

The use of X-rays for medical purposes

In addition to detecting bone fractures, x-rays are widely used for medical purposes. The specialized application of x-rays is to achieve the following goals:

1. To destroy cancer cells.
2. To reduce the size of the tumor.
3. To reduce pain.

For example, radioactive iodine, used in endocrinological diseases, is actively used in thyroid cancer, thereby helping many people get rid of this terrible disease. Currently, to diagnose complex diseases, X-rays are connected to computers, as a result, the latest research methods appear, such as computed axial tomography.

Such a scan provides doctors with color images that show the internal organs of a person. To detect the work of internal organs, a small dose of radiation is sufficient. X-rays are also widely used in physiotherapy.

Basic properties of X-rays

1. penetrating ability. All bodies are transparent to the X-ray, and the degree of transparency depends on the thickness of the body. It is due to this property that the beam began to be used in medicine to detect the functioning of organs, the presence of fractures and foreign bodies in the body.
2. They are able to cause the glow of some objects. For example, if barium and platinum are applied to cardboard, then, after passing through the beam scanning, it will glow greenish-yellow. If you place your hand between the X-ray tube and the screen, then the light will penetrate more into the bone than into the tissue, so the bone tissue will be highlighted most brightly on the screen, and the muscle tissue will be less bright.
3. Action on film. X-rays can, like light, make film dark, this allows you to photograph the shadow side that is obtained when X-rays of bodies are examined.
4. X-rays can ionize gases. This makes it possible not only to find rays, but also to reveal their intensity by measuring the ionization current in the gas.
5. They have a biochemical effect on the body of living beings. Thanks to this property, X-rays have found their wide application in medicine: they can treat both skin diseases and diseases of internal organs. In this case, the desired dosage of radiation and the duration of the rays are selected. Prolonged and excessive use of such treatment is very harmful and detrimental to the body.

The consequence of the use of X-rays was the saving of many human lives. X-ray helps not only to diagnose the disease in a timely manner, treatment methods using radiation therapy relieve patients of various pathologies, from hyperfunction of the thyroid gland to malignant tumors of bone tissues.

a brief description of x-ray radiation

X-rays are electromagnetic waves (flux of quanta, photons), the energy of which is located on the energy scale between ultraviolet radiation and gamma radiation (Fig. 2-1). X-ray photons have energies from 100 eV to 250 keV, which corresponds to radiation with a frequency of 3×10 16 Hz to 6×10 19 Hz and a wavelength of 0.005–10 nm. The electromagnetic spectra of x-rays and gamma rays overlap to a large extent.

Rice. 2-1. Electromagnetic radiation scale

The main difference between these two types of radiation is the way they occur. X-rays are obtained with the participation of electrons (for example, during the deceleration of their flow), and gamma rays - with the radioactive decay of the nuclei of some elements.

X-rays can be generated during deceleration of an accelerated flow of charged particles (the so-called bremsstrahlung) or when high-energy transitions occur in the electron shells of atoms (characteristic radiation). Medical devices use X-ray tubes to generate X-rays (Figure 2-2). Their main components are a cathode and a massive anode. Electrons emitted due to difference electrical potentials between the anode and the cathode, accelerate, reach the anode, upon collision with the material of which they are slowed down. As a result, bremsstrahlung X-rays are produced. During the collision of electrons with the anode, the second process also occurs - electrons are knocked out of the electron shells of the anode atoms. Their places are occupied by electrons from other shells of the atom. During this process, a second type of X-ray radiation is generated - the so-called characteristic X-ray radiation, the spectrum of which largely depends on the anode material. Anodes are most often made of molybdenum or tungsten. There are special devices for focusing and filtering X-rays in order to improve the resulting images.

Rice. 2-2. Scheme of the X-ray tube device:

The properties of X-rays that determine their use in medicine are penetrating power, fluorescent and photochemical effects. Penetrating power of X-rays and their absorption by tissues human body and artificial materials are the most important properties that determine their use in radiation diagnostics. The shorter the wavelength, the greater the penetrating power of X-rays.

Distinguish between "soft" X-ray radiation with low energy and radiation frequency (respectively, with the largest wavelength) and "hard" X-ray radiation with high photon energy and radiation frequency, having a short wavelength. The wavelength of X-ray radiation (respectively, its "hardness" and penetrating power) depends on the magnitude of the voltage applied to the X-ray tube. The higher the voltage on the tube, the greater the speed and energy of the electron flow and the shorter the wavelength of the x-rays.

During the interaction of X-ray radiation penetrating through the substance, qualitative and quantitative changes occur in it. The degree of absorption of X-rays by tissues is different and is determined by the density and atomic weight of the elements that make up the object. The higher the density and atomic weight of the substance of which the object (organ) under study consists, the more X-rays are absorbed. The human body contains tissues and organs of different densities (lungs, bones, soft tissues, etc.), which explains the different absorption of X-rays. The visualization of internal organs and structures is based on the artificial or natural difference in the absorption of X-rays by various organs and tissues.

To register the radiation that has passed through the body, its ability to cause fluorescence of certain compounds and to have a photochemical effect on the film is used. For this purpose, special screens for fluoroscopy and photographic films for radiography are used. In modern X-ray machines, special systems of digital electronic detectors - digital electronic panels - are used to register attenuated radiation. In this case, X-ray methods are called digital.

Due to the biological effect of X-rays, it is necessary to protect patients during the examination. This is achieved

the shortest possible exposure time, the replacement of fluoroscopy with radiography, the strictly justified use of ionizing methods, protection by shielding the patient and staff from exposure to radiation.

X-rays are a type of high-energy electromagnetic radiation. It is actively used in various branches of medicine.

X-rays are electromagnetic waves whose photon energy on the scale of electromagnetic waves is between ultraviolet radiation and gamma radiation (from ~10 eV to ~1 MeV), which corresponds to wavelengths from ~10^3 to ~10^−2 angstroms ( from ~10^−7 to ~10^−12 m). That is, it is incomparably harder radiation than visible light, which is on this scale between ultraviolet and infrared ("thermal") rays.

The boundary between X-rays and gamma radiation is distinguished conditionally: their ranges intersect, gamma rays can have an energy of 1 keV. They differ in origin: gamma rays are emitted during processes occurring in atomic nuclei, while X-rays are emitted during processes involving electrons (both free and those in the electron shells of atoms). At the same time, it is impossible to establish from the photon itself during which process it arose, that is, the division into the X-ray and gamma ranges is largely arbitrary.

The x-ray range is divided into "soft x-ray" and "hard". The boundary between them lies at the wavelength level of 2 angstroms and 6 keV of energy.

The X-ray generator is a tube in which a vacuum is created. There are electrodes - a cathode, to which a negative charge is applied, and a positively charged anode. The voltage between them is tens to hundreds of kilovolts. The generation of X-ray photons occurs when electrons "break" from the cathode and crash into the surface of the anode at high speed. The resulting X-ray radiation is called "bremsstrahlung", its photons have different wavelengths.

At the same time, photons of the characteristic spectrum are generated. Part of the electrons in the atoms of the anode substance is excited, that is, it goes to higher orbits, and then returns to its normal state, emitting photons of a certain wavelength. Both types of X-rays are produced in a standard generator.

Discovery history

On November 8, 1895, the German scientist Wilhelm Conrad Roentgen discovered that some substances under the influence of "cathode rays", that is, the flow of electrons generated by a cathode ray tube, begin to glow. He explained this phenomenon by the influence of certain X-rays - so (“X-rays”) this radiation is now called in many languages. Later V.K. Roentgen studied the phenomenon he had discovered. On December 22, 1895, he gave a lecture on this topic at the University of Würzburg.

Later it turned out that X-ray radiation had been observed before, but then the phenomena associated with it were not given of great importance. The cathode ray tube was invented a long time ago, but before V.K. No one took X-rays special attention on blackening of photographic plates near it, etc. phenomena. The danger posed by penetrating radiation was also unknown.

Types and their effect on the body

"X-ray" is the mildest type of penetrating radiation. Overexposure to soft x-rays is similar to ultraviolet exposure, but in a more severe form. A burn forms on the skin, but the lesion is deeper, and it heals much more slowly.

Hard X-ray is a full-fledged ionizing radiation that can lead to radiation sickness. X-ray quanta can break the protein molecules that make up the tissues of the human body, as well as the DNA molecules of the genome. But even if an X-ray quantum breaks a water molecule, it doesn't matter: chemically active free radicals H and OH are formed, which themselves are able to act on proteins and DNA. Radiation sickness proceeds in a more severe form, the more the hematopoietic organs are affected.

X-rays have mutagenic and carcinogenic activity. This means that the probability of spontaneous mutations in cells during irradiation increases, and sometimes healthy cells can degenerate into cancerous ones. Increasing the likelihood of malignant tumors is a standard consequence of any exposure, including x-rays. X-rays are the least dangerous type of penetrating radiation, but they can still be dangerous.

X-ray radiation: application and how it works

X-ray radiation is used in medicine, as well as in other areas of human activity.

Fluoroscopy and computed tomography

The most common use of X-rays is fluoroscopy. "Transillumination" of the human body allows you to get a detailed image of both the bones (they are most clearly visible) and images of the internal organs.

Different transparency of body tissues in x-rays is associated with their chemical composition. Features of the structure of bones is that they contain a lot of calcium and phosphorus. Other tissues are composed mainly of carbon, hydrogen, oxygen and nitrogen. The phosphorus atom is almost twice as heavy as the oxygen atom, and the calcium atom is 2.5 times (carbon, nitrogen and hydrogen are even lighter than oxygen). In this regard, the absorption of X-ray photons in the bones is much higher.

In addition to two-dimensional "pictures", radiography makes it possible to create a three-dimensional image of an organ: this kind of radiography is called computed tomography. For these purposes, soft x-rays are used. The amount of exposure received in one picture is small: it is approximately equal to the exposure received during a 2-hour flight in an airplane at an altitude of 10 km.

X-ray flaw detection allows you to detect small internal defects in products. A hard X-ray is used for it, since many materials (metal, for example) are poorly “translucent” due to the high atomic mass of their constituent substance.

X-ray diffraction and X-ray fluorescence analysis

X-rays have properties that allow them to examine individual atoms in detail. X-ray diffraction analysis is actively used in chemistry (including biochemistry) and crystallography. The principle of its operation is the diffraction scattering of X-rays by atoms of crystals or complex molecules. Using X-ray diffraction analysis, the structure of the DNA molecule was determined.

X-ray fluorescence analysis allows you to quickly determine chemical composition substances.

There are many forms of radiotherapy, but they all involve the use of ionizing radiation. Radiotherapy is divided into 2 types: corpuscular and wave. Corpuscular uses flows of alpha particles (nuclei of helium atoms), beta particles (electrons), neutrons, protons, heavy ions. Wave uses rays of the electromagnetic spectrum - x-rays and gamma.

Radiotherapy methods are used primarily for the treatment of oncological diseases. The fact is that radiation primarily affects actively dividing cells, which is why the hematopoietic organs suffer this way (their cells are constantly dividing, producing more and more new red blood cells). Cancer cells are also constantly dividing and are more vulnerable to radiation than healthy tissue.

A level of radiation is used that suppresses the activity of cancer cells, while moderately affecting healthy ones. Under the influence of radiation, it is not the destruction of cells as such, but the damage to their genome - DNA molecules. A cell with a destroyed genome may exist for some time, but can no longer divide, that is, tumor growth stops.

Radiation therapy is the mildest form of radiotherapy. Wave radiation is softer than corpuscular radiation, and X-rays are softer than gamma radiation.

During pregnancy

It is dangerous to use ionizing radiation during pregnancy. X-rays are mutagenic and can cause abnormalities in the fetus. X-ray therapy is incompatible with pregnancy: it can only be used if it has already been decided to have an abortion. Restrictions on fluoroscopy are softer, but in the first months it is also strictly prohibited.

In case of emergency, X-ray examination is replaced by magnetic resonance imaging. But in the first trimester, they try to avoid it too (this method has appeared recently, and with absolute certainty to speak about the absence of harmful consequences).

An unequivocal danger arises when exposed to a total dose of at least 1 mSv (in old units - 100 mR). With a simple x-ray (for example, when undergoing fluorography), the patient receives about 50 times less. In order to receive such a dose at a time, you need to undergo a detailed computed tomography.

That is, the mere fact of a 1-2-fold "X-ray" at an early stage of pregnancy does not threaten with serious consequences (but it is better not to risk it).

Treatment with it

X-rays are used primarily in the fight against malignant tumors. This method is good because it is highly effective: it kills the tumor. It is bad because healthy tissues are not much better, there are numerous side effects. The organs of hematopoiesis are at particular risk.

In practice, various methods are used to reduce the effect of x-rays on healthy tissues. The beams are directed at an angle in such a way that a tumor is in the zone of their intersection (due to this, the main absorption of energy occurs just there). Sometimes the procedure is performed in motion: the patient's body rotates relative to the radiation source around an axis passing through the tumor. At the same time, healthy tissues are in the irradiation zone only sometimes, and the sick - all the time.

X-rays are used in the treatment of certain arthrosis and similar diseases, as well as skin diseases. Wherein pain syndrome reduced by 50-90%. Since the radiation is used in this case is softer, side effects similar to those that occur in the treatment of tumors are not observed.