X-ray styling. Method and technique for obtaining an x-ray
Name: Atlas of X-ray anatomy and styling. Guide for doctors.
Rostovtsev M.V.
The year of publishing: 2017
The size: 9.08 MB
Format: pdf
Language: Russian
The second edition of the book "Atlas of X-ray anatomy and laying. A guide for doctors" considers the main issues of human X-ray anatomy, provides the basic principles and X-ray laying for the study of a particular area of the human body, organ system. The manual "Atlas of X-ray anatomy and laying" consists of 2 parts - in the first part, X-ray anatomy of the osteoarticular system is characterized, X-ray placements are given in the study of the osteoarticular system, and contrast agents in X-ray diagnostics are presented separately. The second part of the book deals with X-ray examination of internal organs and organ systems. Separate chapters are devoted to such issues as the features of X-ray examination of children, radiation protection during X-ray examination. The book "Atlas of X-ray anatomy and styling. A guide for physicians" is aimed at radiologists, clinical residents and students.
Name: Radiation diagnostics in traumatology and orthopedics
McKinnis Lynn N.
The year of publishing: 2015
The size: 114.04 MB
Format: pdf
Language: Russian
Description: Lynn N. McKinnis, Ed., Lynn N. McKinnis, Clinical Manual, Imaging in Traumatology and Orthopedics, reviews the general principles of musculoskeletal imaging in clinical practice. And... Download the book for free
Name: Radiography in the diagnosis of diseases of the chest. Part 1.
Melnikov V.V.
The year of publishing: 2017
The size: 67.91 MB
Format: pdf
Language: Russian
Description: The textbook "X-ray in the diagnosis of diseases of the chest" in the first part examines the radiographic picture of the most common diseases of the chest, characterizing the syndrome ... Download the book for free
Name: Radiography in the diagnosis of diseases of the chest. Part 2. Additions.
Melnikov V.V.
The year of publishing: 2018
The size: 32.96 MB
Format: pdf
Language: Russian
Description: The second part of the textbook "X-ray in the diagnosis of diseases of the chest" considers the radiographic characteristics of diseases such as fungal infections of the lungs, echinosis ... Download the book for free
Name: Radiography in the diagnosis of diseases of the chest
Melnikov V.V.
The year of publishing: 2017
The size: 67.66 MB
Format: pdf
Language: Russian
Description: A practical guide "X-ray in the diagnosis of diseases of the chest" under the editorship of V. V. Melnikov, considers the principles of diagnosing pathological diseases of the chest ... Download the book for free
Name: Neuroimaging of structural and hemodynamic disorders in brain injury
Zakharova N.E., Kornienko V.N., Potapov A.A., Pronin I.N.
The year of publishing: 2013
The size: 117.3 MB
Format: djvu
Language: Russian
Description: Practical guide "Neuroimaging of structural and hemodynamic disorders in brain injury" ed., Zakharova N.E., et al., considers the clinical diagnostic features of neuroimaging ... Download the book for free
Name: Emergency radiology. Part 1. Traumatic emergencies
Dondelinger R., Marinchek B.
The year of publishing: 2008
The size: 52.33 MB
Format: pdf
Language: Russian
Description: In the practical guide "Emergency Radiology. Part 1. Traumatic Emergencies" ed., Dondelinger R., et al., consider most types of traumatic injuries ... Download the book for free
Name: Atlas of Normal Anatomy of Magnetic Resonance and Computed Tomography of the Brain
Vlasov E.A., Baibakov S.E.
The year of publishing: 2015
The size: 127.72 MB
Format: pdf
Language: Russian
Description:"Atlas of normal anatomy of magnetic resonance and computed tomography of the brain" is devoted to the actual problem of neuromorphology and craniology - intravital macroscopic characteristics of the head ... Download the book for free
Name: Radiation diagnostics in dentistry
Trofimova T.N., Garapach I.A., Belchikova N.S.
The year of publishing: 2010
The size: 106.39 MB
Format: pdf
Language: Russian
Description: The book "Radial diagnostics in dentistry" edited by Trofimova T.N.
Genre: Diagnostics
Format:PDF
Quality: Scanned pages
Description: The X-ray image is the main source of information for substantiating the X-ray conclusion. In fact, this is a complex combination of many shadows that differ from each other in shape, size, optical density, structure, outline of contours, etc. an unevenly attenuated X-ray beam passed through the object under study.
X-ray radiation, as is known, refers to electromagnetic radiation, it arises as a result of deceleration of fast moving electrons at the moment of their collision with the anode of an X-ray tube. The latter is an electrovacuum device that converts electrical energy into X-ray energy. Any X-ray tube (X-ray emitter) consists of a glass container with a high degree of rarefaction and two electrodes: a cathode and an anode. The cathode of the x-ray emitter has the form of a linear spiral and is connected to the negative pole of a high voltage source. The anode is made in the form of a massive copper rod. Its surface facing the cathode (the so-called mirror)7 is beveled at an angle of 15-20° and covered with a refractory metal - tungsten or molybdenum. The anode is connected to the positive pole of a high voltage source.
The tube works as follows: before turning on the high voltage, the cathode filament is heated by a low voltage current (6-14V, 2.5-8A). In this case, the cathode begins to emit free electrons (electron emission), which form an electron cloud around it. When a high voltage is turned on, the electrons rush to the positively charged anode, and upon collision with it, a sharp deceleration occurs and their kinetic energy is converted into thermal energy and X-ray energy.
The amount of current through the tube depends on the number of free electrons, the source of which is the cathode. Therefore, by changing the voltage in the filament circuit of the tube, one can easily control the intensity of X-ray radiation. The radiation energy depends on the potential difference at the electrodes of the tube. It increases with increasing voltage. This reduces the wavelength and increases the penetrating power of the resulting radiation.
The use of X-rays for the clinical diagnosis of diseases is based on its ability to penetrate various organs and tissues that do not transmit visible light rays, and cause the luminescence of certain chemical compounds (activated zinc and cadmium sulfides, calcium tungstate crystals, barium platinum-cyanogen), and also provide photochemical effect on the radiographic film or change the initial potential of the selenium layer of the electro-radiographic plate.
It should be noted right away that the x-ray image differs significantly from the photographic image, as well as the conventional optical image created by visible light. It is known that electromagnetic waves of visible light emitted by bodies or reflected from them, falling into the eye, cause visual sensations that create an image of the object. In the same way, a photographic image displays only the appearance of a photographic object. The X-ray image, unlike the photographic image, reproduces the internal structure of the body under study and is always enlarged.
X-ray image in clinical practice is formed in the system: X-ray emitter (tube - object of study - examined person) - image receiver (X-ray film, fluorescent screen, semiconductor plate). It is based on the uneven absorption of X-ray radiation by various anatomical structures, organs and tissues of the subject.
As is known, the intensity of X-ray absorption depends on the atomic composition, density and thickness of the object under study, as well as on the radiation energy. Ceteris paribus, the heavier the chemical elements entering the tissue and the greater the density and thickness of the layer, the more intensely the X-ray radiation is absorbed. Conversely, tissues composed of elements with a low atomic number usually have a low density and absorb X-rays to a lesser extent.
"Atlas of laying in X-ray studies"
METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE
- X-ray image and its properties
- X-ray technique
STYLING
- Head
- Spine
- limbs
- Breast
- Stomach
X-RAY IMAGE AND ITS PROPERTIES
film or change the initial potential of the selenium layer of electro-rent
genographic plate.
It should be immediately noted that the X-ray image is significantly
differs from photographic, as well as conventional optical, created
exposed to visible light. It is known that electromagnetic waves in the visible
light emitted by bodies or reflected from them, falling into the eye, cause
visual sensations that create an image of an object. Exactly
likewise, a photographic image reflects only the appearance of the photographic
cal object. The X-ray image, in contrast to the photographic
logically reproduces the internal structure of the body under study and always
is enlarged.
X-ray image in clinical practice is formed
in the system: X-ray emitter (tube - object of study -
examined person) - image receiver (radiographic
film, fluorescent screen, semiconductor wafer). At the core
its production lies in the uneven absorption of X-rays
various anatomical structures, organs and tissues of the examination
As is known, the intensity of X-ray absorption
depends on the atomic composition, density and thickness of the object under study,
as well as from the radiation energy. Other things being equal, the heavier
chemical elements included in the tissue and more density and thickness
layer, the more intense the absorption of x-rays. And vice versa,
tissues composed of low atomic number elements usually have
low density and absorb X-rays in a smaller
It has been established that if the relative coefficient of absorption of rent-
of gene radiation of medium hardness by water is taken as 1, then for air
it will be 0.01; for adipose tissue - 0.5; calcium carbonate - 15,
calcium phosphate - 22. In other words, the most x-ray
radiation is absorbed by the bones, to a much lesser extent -
soft tissues (especially fatty) and least of all - tissues containing
puffing air.
Uneven absorption of X-rays in tissues
of the anatomical region under study determines the formation in
space behind the object of a modified or inhomogeneous x-ray beam
new beams (exit dose or dose behind the object). In fact, this bundle
contains images invisible to the eye (images in a beam).
By acting on a fluorescent screen or radiographic film,
it creates a familiar x-ray image.
From the foregoing, it follows that for the formation of X-ray
image requires unequal absorption of X-ray radiation
cheniya in the studied organs and tissues. This is the first absorption law
the so-called x-ray differentiation. Its essence is
in that any object (any anatomical structure) can cause
to show the appearance on the radiograph (electroroentgenogram) or on the transillumination
distinguishing screen of a separate shadow only if it differs
from the surrounding objects (anatomical structures) according to the atomic
composition, density and thickness (Fig. 1).
However, this law is not comprehensive. Various anatomy
mic structures can absorb x-rays in different ways,
but not give a differentiated image. This happens, in particular,
Rice. 1. Scheme of differential
roentgen
images of anatomical
structures with different
density and thickness
(cross section of the thigh).
1 - x-ray emitter;
2 - soft tissues; 3 - short-
the thoracic substance of the femur;
4 - bone marrow cavity;
5 - x-ray receiver
fermentation; 6 - x-ray
image of the cortex
stva; 8 - x-ray image
bone marrow damage
Rice. 2. Lack of differential
cited is depicted and I raz-
fabrics of personal density
at a perpendicular to-
the board of a beam of roentgens -
radiation to their surface
Rice. 3. Distinct differential
rendered image
shadows with different
density at tangential
nom direction of the beam
gene radiation to their
surfaces.
when the X-ray beam is directed perpendicular to
surfaces of each of the media with different transparency (Fig. 2).
However, if you change the spatial relationship between the
surfaces of the structures under study and an X-ray beam
rays, so that the path of the rays corresponds to the direction of these surfaces,
then each object will give a differentiated image (Fig. 3). Such
conditions, various anatomical structures are most clearly displayed
shrink when the central X-ray beam is directed
tangent to their surface. This is the essence of the tangential law.
BASIC PROPERTIES
X-RAY
IMAGES
As already noted, the x-ray image is formed when
the passage of the X-ray beam through the object under study,
having an uneven structure. In this case, the radiation beam on its
the path crosses many points, each of which, to one degree or another
(according to atomic mass, density and thickness) absorbs it
energy. However, the total attenuation of the radiation intensity is not
depends on the spatial arrangement of the individual absorbing it
points. This regularity is schematically presented in fig. four.
Obviously, all points that cause the same attenuation in total
beam of X-ray radiation, despite the different spatial
location in the object under study, in the picture taken in one
projections are displayed on the same plane as shadows of the same
intensity.
This pattern indicates that the X-ray image
the reduction is planar and summative,
Summation and planar nature of the x-ray image
can cause not only summation, but also subtraction (subtraction)
shadows of the studied structures. So, if in the way of X-ray radiation
there are areas of both compaction and rarefaction, then their increased
absorption in the first case is compensated by a reduced in the second
(Fig. 5). Therefore, when studying in one projection, it is not always possible
to distinguish true compaction or rarefaction in the image of one or
another organ from summation or, conversely, subtraction of shadows, located
along the path of the X-ray beam.
This implies a very important rule of X-ray examination.
research: to obtain a differentiated image of all anatomy
ical structures of the area under study, one should strive to take pictures as
at least two (preferably three) mutually perpendicular projections:
direct, lateral and axial (axial) or resort to aiming
shooting, turning the patient behind the screen of the translucent device
It is known that X-rays propagate from a place
its formation (focus of the emitter anode) in the form of a divergent
beam. As a result, the x-ray image is always magnified.
The degree of projection increase depends on the spatial relationship
relations between the x-ray tube, the object under study and the receiver
nick image. This dependence is expressed as follows. At
constant distance from the object to the image receiver than
the smaller the distance from the focus of the tube to the object under study, the more
projection increase is more pronounced. As the increase
focal length, the size of the x-ray image is reduced
and approach the true ones (Fig. 7). The opposite pattern
observed with an increase in the distance "object - image receiver"
niya” (Fig. 8).
With a significant distance of the object under study from the radiographic
film or other image sensor image size
of its details significantly exceeds their true dimensions.
METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE
Rice. 4. Identical total
new image of several
points on the image at different
nom spatial dis-
their position in the study
my object (according to V. I. Feok-
tistova).
Rice. 5. Summation effect (a)
and subtraction (b) shadows.
Projection magnification of the x-ray image in each
tube - image receiver "to the distance" focus of the tube - research-
thought object." If these distances are equal, then the projection magnification
is practically non-existent. However, in practice, between the studied
there is always some distance between the object and the radiographic film
which causes a projection increase in the X-ray image
zheniya. It should be borne in mind that when shooting the same
anatomical region, its various structures will be located at different
distance from the focus of the tube and the image receiver. For example, on
direct anterior chest x-ray image of the anterior sections
ribs will be enlarged to a lesser extent than the rear.
Quantitative dependence of the projection magnification of the image
structures of the object under study (in %) from the distance "tube focus -
film” (RFTP) and the distances from these structures to the film are shown in Table. one
[Sokolov V. M., 1979].
X-RAY IMAGE AND ITS PROPERTIES
Rice. 6. X-ray
research carried out in
two mutually perpendicular
lar projections.
a - summation; 6 times-
good image of shadows
dense structures.
Rice. 7. Dependence between
tube focus distance -
object and projection
x-ray
Images.
With an increase in the focal length
standing projection magnification
x-ray imaging
niya decreases.
Rice. 8. Dependence between
distance object - at-
image receiver and projector
rational increase in rent-
gene image.
With increasing distance
ect - image receiver
projective increase in rent-
gene image
METHOD AND TECHNIQUE OF OBTAINING X-RAY
TABLE 1
Projection dependency
increase in research structures
inflated object (in %) from
RFTP and distances from these
structures before the film
Distance from
object structures up to
films, ate
Rice. 9. Changing the edge
aching areas of the skull with
increasing the focal length
ab - edge-forming points
at minimum focal length
distance (fi); aib] - edge-
splitting points at significant
nominal focal length (b).
From the foregoing, it is clear that in those cases
when it is necessary that the dimensions of the x-ray
th images were close to true, it follows
bring the object under study as close as possible to
cassette or translucent screen and remove
handset as far as possible.
When the last condition is met,
take into account the power of X-ray diagnostic
apparatus, since the radiation intensity changes inversely
rationally to the square of the distance. Usually in practical work the focal
the distance is increased to a maximum of 2-2.5 m (teleroentgenography).
Under these conditions, the projection magnification of the x-ray image
happens to be minimal. For example, an increase in the transverse size of the heart
when shooting in direct frontal projection will be only 1-2 mm (depending on
dependence on removal from the film). In practical work, it is also necessary
take into account the following circumstance: when changing RFTP in education
contours of the shadow of the object under study, various
plots. So, for example, in the pictures of the skull in direct anterior projection
X-RAY IMAGE AND ITS PROPERTIES
Rice. 10, Projection reduction
x-ray imaging
linear
forms depending on
location in relation
to the central bundle of rent-
gene radiation.
Rice. 11. The image is flat
bone formation at
direction of the central
X-ray beam
niya perpendicular to it
and to the image receiver
(a) and with the direction of the cent-
ral beam along the plane
bone formation (b).
at the minimum focal length, the edge-formers are
areas located closer to the tube, and with a significant RFTP -
located closer to the image receiver (Fig. 9).
Although the x-ray image is in principle always
is increased, under certain conditions, a project is observed
rational reduction of the object under study. Typically, this reduction
concerns the image of planar formations or structures that have
linear, oblong shape (bronchi, vessels), if their main axis is not
parallel to the image receptor plane and not perpendicular
the central X-ray beam (Fig. 10).
It is obvious that the shadows of the bronchi, as well as vessels or any other
objects of an oblong shape have a maximum size in those cases
teas, when their main axis (in parallel projection) is perpendicular
to the direction of the central beam. As you decrease or increase
the angle formed by the central beam and the length of the object under study,
METHOD AND TECHNIQUE OF OBTAINING X-RAY
Rice. 12. Image distortion
ball compression during X-ray
a logical study of co-
sym beam (a) or with an oblique
location (relative to
to the central beam) reception-
image nick (b).
Rice. 13. "Normal" image
spherical objects
(a) and oblong (b)
we are in oblique research
projections.
Tube and cassette position
changed in such a way that
central beam of x-rays
radiation passed through
cut the center of the object perpendicular-
cassette. Longitudinal axis
oblong object
runs parallel to the plane
cassette bones.
the size of the shadow of the latter gradually decreases. In orthograde projection
tion (along the central beam) a blood-filled vessel, like any
linear formation, displayed as a dotted homogeneous shadow,
the bronchus has the form of a ring. The combination of such shadows is usually determined
on the pictures or on the screen of the X-ray machine when translucent
Unlike the shadows of other anatomical structures (compacted
lymph nodes, dense focal shadows) when turning, they
become linear.
Similarly, the formation of X-ray
images of planar formations (in particular, with interlobar
pleurisy). The maximum dimensions of the shadow of a planar formation are
X-RAY IMAGE AND ITS PROPERTIES
in cases where the central radiation beam is directed perpendicular to
cularly to the plane under study and the film. If it passes along
planar formation (orthograde projection), then this formation
displayed on the picture or on the screen as an intense linear shadow
It must be borne in mind that in the options considered, we proceeded
from the fact that the central beam of x-rays passes through
center of the object under study and directed to the center of the film (screen) under
right angle to its surface. This is usually sought in x-ray
diagnostics. However, in practical work, the object under study is often
is located at some distance from the central beam or a cassette with film
which or the screen are not at right angles to it (oblique projection).
In such cases, due to an uneven increase in individual segments
object, its image is deformed. So, the bodies are spherical
shape are stretched mainly in one direction and
take the form of an oval (Fig. 12). With such distortions, most often
encountered when examining some joints (heads
femur and humerus), as well as when performing intraoral
dental pictures.
To reduce projection distortion in each specific
case, it is necessary to achieve optimal spatial relationships
relations between the object under study, the image receiver
and central beam. To do this, the object is placed parallel to the film.
(screen) and through its central section and perpendicular to the film
direct the central beam of x-rays. If for those or
other reasons (forced position of the patient, structural features
anatomical region) it is not possible to give the object
desired position, normal shooting conditions are achieved
by appropriately changing the position of the focus of the tube and receiving
image nickname - cassette (without changing the position of the patient), as it is
shown in fig. 13.
SHADOW INTENSITY
X-RAY
IMAGES
The intensity of the shadow of a particular anatomical structure depends
from its "radio transparency", that is, the ability to absorb x-ray
radiation. This ability, as already mentioned, is determined by the atomic
composition, density and thickness of the object under study. The harder
chemical elements included in the anatomical structures, the more
they absorb x-rays. A similar dependence exists
varies between the density of the objects under study and their X-ray transmission
value: the greater the density of the object under study, the more intense
his shadow. That is why X-ray examination usually
metal foreign bodies are easily identified and the search is very difficult
foreign bodies having a low density (wood, various types
plastics, aluminum, glass, etc.).
Depending on the density, it is customary to distinguish 4 degrees of transparency
media: air, soft tissue, bone and metal. Thus
METHOD AND TECHNIQUE OF OBTAINING X-RAY SHOT
Therefore, it is obvious that when analyzing an X-ray image, it is
which is a combination of shadows of different intensities, it is necessary to take into account
to determine the chemical composition and density of the studied anatomical structures.
In modern X-ray diagnostic complexes that allow the use of
call computer technology (computed tomography), there is a possibility
the ability to confidently determine the nature of the
tissues (fat, muscle, cartilage, etc.) in normal and pathological
conditions (soft tissue neoplasm; cyst containing
liquid, etc.).
However, under normal circumstances, it should be borne in mind that most
tissues of the human body in terms of their atomic composition and density
slightly different from each other. So, muscles, parenchymal
organs, brain, blood, lymph, nerves, various soft tissue pathological
formations (tumors, inflammatory granulomas), as well as pathological
cal fluids (exudate, transudate) have almost the same
"radio transparency". Therefore, often a decisive influence on the intensity
the intensity of the shadow of a particular anatomical structure has a change
its thickness.
It is known, in particular, that with an increase in the thickness of the body in arithmetic
x-ray beam behind the object (exit dose)
decreases exponentially, and even slight fluctuations
changes in the thickness of the structures under study can significantly change the intensity
the intensity of their shadows.
As seen in fig. 14, when shooting an object having the shape of a triangular
prism (for example, the pyramid of the temporal bone), the highest intensity
Shade areas corresponding to the maximum thickness of the object have the highest density.
So, if the central beam is directed perpendicular to one of the sides
the base of the prism, then the intensity of the shadow will be maximum in the central
nom department. In the direction of the periphery, its intensity gradually
decreases, which fully reflects the change in tissue thickness,
located on the path of the X-ray beam (Fig. 14, a). If
rotate the prism (Fig. 14, b) so that the central beam is directed
tangential to any side of the prism, then the maximum intensity
ness will have an edge portion of the shadow corresponding to the maximum
(in this projection) the thickness of the object. Similarly, increases
the intensity of shadows that have a linear or oblong shape in those
cases where the direction of their main axis coincides with the direction
central beam (orthograde projection).
When examining homogeneous objects with a rounded or
cylindrical shape (heart, large vessels, tumor), thickness
tissues along the x-ray beam changes very slightly
seriously. Therefore, the shadow of the object under study is almost homogeneous (Fig. 14, c).
If a spherical or cylindrical anatomical formation
has a dense wall and is hollow, then the X-ray beam
in the peripheral parts passes a larger volume of tissues, which
causes the appearance of more intense blackout areas in the peripheral
sections of the image of the object under study (Fig. 14, d). It's so called-
my "marginal borders". Such shadows, in particular, are observed in the study
tubular bones, vessels with partially or completely calcified
ny walls, cavities with dense walls, etc.
It should be borne in mind that in practical work for differentiating
bathroom perception of each particular shadow is often decisive
X-RAY IMAGE AND ITS PROPERTIES
Rice. 14. Schematic representation
shadow intensity display
various objects depending on
bridges from their shape, position
niya and structures.
a, b - trihedral prism; in -
solid cylinder; g - hollow
has not absolute intensity, but contrast, i.e., the difference in intensity
the intensity of this and surrounding shadows. At the same time, the importance of
acquire physical and technical factors that affect the contact
image density: radiation energy, exposure, presence of sifting
gratings, raster efficiency, the presence of intensifying screens, etc.
Incorrectly selected technical conditions (excessive voltage on
tube, too much or, conversely, insufficient exposure, low
raster efficiency), as well as errors in photochemical processing
films reduce the contrast of the image and thereby have a negative
significant influence on the differentiated detection of individual shadows
and an objective assessment of their intensity.
FACTORS DETERMINING
INFORMATION
X-RAY
IMAGES
The informativeness of the x-ray image is estimated by the volume
useful diagnostic information that the doctor receives when studying
picture. Ultimately, it is distinguished by
photographs or a translucent screen of the details of the object under study.
From a technical point of view, the quality of an image is determined by its
optical density, contrast and sharpness.
Optical density. It is well known that X-ray exposure
radiation on the photosensitive layer of the radiographic film
causes changes in it, which, after appropriate processing
appear as blackening. The intensity of blackening depends on the dose
X-ray radiation absorbed by the photosensitive layer
films. Usually the maximum blackening is observed in those areas
films that are exposed to a direct beam of radiation,
passing by the investigated object. Blackening intensity
other sections of the film depends on the nature of the tissues (their density and thickness
tires) located in the path of the X-ray beam. For
an objective assessment of the degree of blackening of the manifested radiographic
film and introduced the concept of "optical density".
METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE
The optical density of the blackening of the film is characterized by a weakening
light passing through the negative. For quantitative expression
optical density, it is customary to use decimal logarithms.
If the intensity of the light incident on the film is denoted by /
And intensive
the intensity of the light passing through it - 1
then the optical density is blackened
Photographic blackening is taken as a unit of optical density.
ion, when passing through which the luminous flux is attenuated by 10 times
(Ig 10 = 1). Obviously, if the film transmits 0.01 part of the incident
light, then the blackening density is equal to 2 (Ig 100 = 2).
It has been established that the visibility of the details of the x-ray image
can be optimal only for well-defined, average values
optical densities. Excessive optical density, as well as
insufficient blackening of the film, accompanied by a decrease in the difference
the purity of image details and the loss of diagnostic information.
A good quality chest image shows an almost transparent shadow
heart has an optical density of 0.1-0.2, and a black background - 2.5. For
normal eye, the optimal optical density fluctuates within
lah from 0.5 to 1.3. This means that for a given range of optical density,
eyelids well captures even slight differences in the degree
blackening. The finest details of the image vary within
blackening 0.7-0.9 [Katsman A. Ya., 1957].
As already noted, the optical density of blackening of radiographic
film depends on the absorbed dose of X-ray
radiation. This dependence for each photosensitive material
can be expressed using the so-called characteristic
curve (Fig. 15). Usually such a curve is drawn in logarithmic
scale: logarithms of doses are plotted along the horizontal axis; vertically
calic - the values of optical densities (logarithms of blackening).
The characteristic curve has a typical shape that allows
allocate 5 areas. Initial section (up to point A), almost parallel
horizontal axis corresponds to the veil zone. This slight blackening
which inevitably occurs on the film when exposed to very small
low doses of radiation or even without radiation as a result of the interaction
parts of halogen silver crystals with developer. Point A represents
is the blackening threshold and corresponds to the dose required in order to
cause a visually perceptible blackening. Segment AB corresponds to
underexposure zone. Blackening densities here increase first
slowly, then quickly. In other words, the nature of the curve (gradual
steepness increase) of this section indicates an increasing
increase in optical density. The BV section has a rectilinear shape.
Here there is an almost proportional dependence of the density of handwriting
from the logarithm of the dose. This is the so-called normal exposure zone.
positions. Finally, the upper portion of the SH curve corresponds to the overexposure zone.
Here, as well as in section AB, there is no proportional dependence
the relationship between optical density and absorbed photosensitive
layer of radiation dose. As a result, in the transmission of X-ray
images are distorted.
From what has been said, it is obvious that in practical work it is necessary to use
be subject to such technical conditions of the film that would provide
X-RAY IMAGE AND ITS PROPERTIES 19
blackening of the film corresponding to the proportional band
characteristic curve.
"Contrast. Under X-Ray Image Contrast
understand the visual perception of the difference in optical densities (degrees
blackening) adjacent areas of the image of the object under study or
the entire object and background. The higher the contrast, the greater the difference.
optical densities of the background and object. So, in high-contrast pictures
limbs, a light, almost white image of the bones is sharply outlined
is painted on a completely black background, corresponding to soft tissues.
It must be emphasized that such an external "beauty" of the picture is not
testifies to its high quality, since excessive contrast
image is inevitably accompanied by the loss of smaller and less
dense details. On the other hand, a sluggish, low-contrast image
also characterized by low information content.
the smallest and most distinct detection in a photograph or translucent
screen of details of the x-ray image of the object under study.
Under ideal conditions, the eye is able to notice the difference in optical density
ness, if it is only 2%, and when studying the radiograph on
negatoscope - about 5%. Small contrasts are better revealed in the pictures,
having a relatively low main optical density.
Therefore, as already mentioned, one should strive to avoid significant
blackening of the x-ray.
The contrast of the x-ray image, perceived by us at
analysis of radiographs, is primarily determined by the so-called
beam contrast. Radiation contrast is the ratio of doses
radiation behind and in front of the object under study (background). This attitude
expressed by the formula:
Beam contrast; D^- background dose; D
Dose by detail
thought object.
Beam contrast depends on the intensity of X-ray absorption
radiation by various structures of the object under study, as well as from energy
gy radiation. The clearer the difference in density and thickness of the studied
structures, the greater the radiation contrast, and consequently, the X-ray contrast
new image.
Significant negative effect on X-ray contrast
images, especially with x-rays (fluoroscopy)
increased rigidity, renders scattered radiation. For decreasing
amount of scattered x-rays use screening
gratings with high raster efficiency (at voltage on the tube
above 80 kV - with a ratio of at least 1:10), and also resort to careful
effective diaphragming of the primary radiation beam and compression
object under study. Under these conditions, radiographs
performed at a relatively high voltage on the tube (80-
110 kV), it is possible to obtain an image with a lot of details,
including anatomical structures that differ significantly in density
or thickness (flattening effect). For this purpose, it is recommended
use special nozzles on the tube with wedge-shaped filters
for spot shots, in particular, those proposed in recent years
L. N. Sysuev.
METHODOLOGY AND TECHNIQUE FOR OBTAINING X-RAY SHOT
Rice. 15. Characteristic
radiographic curve
films.
Explanations in the text.
Rice. 16. Schematic representation
absolutely sharp
(a) and unsharp (b) transition
from one optical plot-
ness to another.
Rice. 17. Dependence sharply
X-ray imaging
focus
x-ray tube (geo-
metric blur).
a - spot focus - image-
the motion is absolutely sharp;
b, c - focus in the form of a platform
different sizes - image
motion is not sharp. With the increase
focus blur increases.
Significant effect on image contrast is
properties of the radiographic film, which are characterized by the coefficient
contrast ratio. Contrast Ratio at shows in
how many times a given x-ray film enhances the natural
contrast of the object under study. Most often in practice
use films that increase natural contrast by 3-3.5 times
(y = 3-3.5). For fluorographic film at = 1,2-1,7.
# Sharpness. The sharpness of an X-ray image is characterized by
features of the transition from one blackening to another. If such
the transition is jump-like, then the shadow elements of X-rays
images are sharp. Their image is a res-
kim. If one blackening passes into another smoothly, there is
"blurring" of the contours and details of the image of the object under study
Unsharpness (“blurring”) of contours always has a certain
width, which is expressed in millimeters. visual perception
blur depends on its magnitude. Thus, when examining radiographs
on a negatoscope, blurring up to 0.2 mm, as a rule, is not visually perceived
is removed and the image appears sharp. Usually our eye notices unsharp-
bone if it is 0.25 mm or more. It is customary to distinguish between geometric
chesky, dynamic, screen and total unsharpness.
Geometrical blurring depends, first of all, on the magni- tude
ranks of the focal spot of the X-ray tube, as well as on the distance
"tube focus - object" and "object - image receiver".
X-RAY IMAGE AND ITS PROPERTIES 21
An absolutely sharp image can only be obtained if
if the X-ray beam comes from a point source
radiation (Fig. 17, a). In all other cases, inevitably formed
penumbra, which smear the contours of image details. How
the greater the width of the focus of the tube, the greater the geometric unsharpness and,
on the contrary, the "sharper" the focus, the less blur (Fig. 17.6, c).
Modern x-ray diagnostic tubes have the following
focal spot dimensions: 0.3 X 0.3 mm (micro focus); from 0.6 X 0.6 mm
up to 1.2 X 1.2 mm (small focus); 1.3 X 1.3; 1.8 X 1.8 and 2 X 2 and up
(big focus). It is obvious that in order to reduce the geometric uncut
bones should use tubes with micro or small sharp focus.
This is especially important for X-rays with direct magnification of X-rays.
image. However, keep in mind that when using
sharp focus, it becomes necessary to increase shutter speed, which
may result in increased dynamic blur. Therefore, micro
focus should be used only when examining stationary objects,
mostly skeletal.
A significant effect on the geometric unsharpness is exerted by
distance "tube focus - film" and distance "object - film".
As the focal length increases, the sharpness of the image increases and,
on the contrary, with increasing distance "object - film" - decreases.
The total geometric unsharpness can be calculated from
where H - geometric unsharpness, mm; f- optical focus width
tubes, mm; h is the distance from the object to the film, cm; F - distance
"tube-film focus", cf.
confusion in each particular case. So, when shooting with a tube with a focus
spot 2 X 2 mm of an object located 5 cm from the radiographic
film, from a focal length of 100 cm geometric unsharpness
will be about 0.1 mm. However, when deleting the object of study on
20 cm from the film, the blur will increase to 0.5 mm, which is already well distinguished
chimo eye. This example shows that we should strive
bring the investigated anatomical area as close as possible to the film.
D ynamic blur is due to motion
object under study during X-ray examination. More often
all it is due to the pulsation of the heart and large vessels,
breathing, peristalsis of the stomach, the movement of patients during shooting
due to an uncomfortable position or motor excitation. When researching
thoracic organs and gastrointestinal tract dynamic
unsharpness in most cases is of the most significant importance.
To reduce dynamic blur, you need (if possible)
take pictures with short exposures. It is known that the linear speed
contraction of the heart and fluctuations of adjacent areas of the lung
approaches 20 mm/s. Amount of dynamic blur when shooting
organs of the chest cavity with a shutter speed of 0.4 s reaches 4 mm. Practically
only a shutter speed of 0.02 s allows you to completely eliminate the distinguishable
eye blurring of the image of the lungs. When examining the gastrointestinal
intestinal tract exposure without compromising image quality can
be increased to 0.2 s.
Rice. 488. Laying for radiography of the ribs during breathing with fixation of the chest with an elastic belt.
a significant increase in the pulmonary pattern (for example, stagnation in the pulmonary circulation).
To overcome the negative influence of the superposition of the lung pattern on the image of the ribs, it is recommended to take pictures of the ribs during the act of breathing.
At the same time, it is necessary to fix the chest. Under such conditions, it is possible to obtain a clear image of the ribs against the background of a blurred lung pattern.
Most often, a prefix proposed by S. I. Finkelstein (1967) is used to fix the chest. It is shown schematically in Fig. 484. Laying is carried out as follows. The patient lies on his stomach. Attachments placed under the chest and hips cause the abdomen to sag and the chest to be fixed by the weight of the body (Fig. 485). Shooting is performed with a shutter speed of 2.5-3 s (normal exposure), without holding the breath. As a rule, during this time the patient manages to take a shallow breath and exhale, without a pause between them. On images taken under such conditions, against the background of a fuzzy ("blurred") image of the lung pattern, the structure of the ribs is more clearly displayed (Fig. 486, 487).
However, in the presence of damage to the ribs, it is usually not possible to put the patient on the stand with the breast; in such cases, the methodological technique proposed by A. Ya. Sheimanidze (1974) can be used. The patient lies on his back. The chest is fixed with an elastic compression belt. Shooting is carried out in the same way as in the previous case (Fig. 488).
The accumulated experience has shown that in case of severe chest injuries with multiple fractures of the ribs, the patient switches to the abdominal type of breathing due to severe pain syndrome,
AT in such cases, when examining the ribs, there is no need to resort to
to special techniques for fixing the breast. Enough
448 STYLING
A picture of the sternum is usually performed in two projections: anterior oblique and lateral. Shooting in a direct projection, as a rule, is not effective, since the image of the sternum against the background of intense shadows of the mediastinal and spinal organs is not differentiated.
WHEN X-RAY OF THE BREAST
Anterior oblique shot of the sternum
In order to exclude the combination of the image of the sternum with the image of the organs of the mediastinum and spine, the right half of the chest is raised above the table so that the frontal plane of the body makes an angle of 25-30 ° with the plane of the cassette (it is not advisable to raise the left half of the chest with emphasis on the right side , since under these conditions it is impossible to avoid the combination
they blow under the sternum, along the table, so that its middle line coincides with the median plane of the patient's torso, and the upper edge is 3-4 cm above the upper edge of the sternum. The central radiation beam is directed vertically, to the center of the cassette, between the inner edge of the scapula and the spine at the level of the body of the fifth thoracic vertebra (Fig. 489, a, b).
Similar ratios are maintained with radiography of the sternum in the patient's standing position.
Rice. 489. Laying for radiography of the sternum in the anterior oblique projection with the patient turned to the left side,
a - the position of the patient; b - schematic representation of the relationship between the central X-ray beam, the region under study and the cassette.
Rice. 490. Laying for radiography of the sternum in the anterior oblique projection without turning the patient.
a - the position of the patient; 6 is a schematic representation of the relationship between the central x-ray beam, the region of interest and the cassette.
Rice. 491. A picture of the sternum in the anterior oblique projection.
Fracture of the sternum with lateral displacement of the body of the sternum to the left.
Anterior oblique sternum imaging can be performed without turning the patient. The patient lies on his stomach. The anterior surface of the chest and the heads of both humerus fit snugly against the cassette. The neck is somewhat elongated, the head is straight, without any turns. The chin rests on the deck of the table. The arms are extended along the body. The central X-ray beam is directed to the sternum region, obliquely from right to left, at an angle of 30 ° to the plane of the cassette, which is placed along the table so that the axis of the sternum passes
dila 5-7 cm to the right of the median longitudinal line of the cassette. This is necessary so that the image of the sternum is in the center of the radiograph (Fig. 490, a, b).
Informative picture. On the anterior oblique images of the sternum,
all its departments, upper, right and left contours are clearly displayed. In this projection, as a rule, lateral displacements of various parts of the sternum are clearly visible, which are usually caused by trauma (Fig. 491).
The criterion for the correctness of the technical conditions of shooting and the correctness laying is a clear isolated image of all parts of the sternum, without imposing images of the organs of the mediastinum and spine on it.
The most common mistakes when taking a picture are inaccurate centering of the X-ray beam, incorrect tilt of the patient's torso or X-ray tube, and incorrect position of the cassette.
STERNUM LATERAL IMAGE
The purpose of the image is to study the state of the anterior, central and posterior sections of the sternum.
Laying the patient to take a picture. X-ray of the sternum is carried out in the position of the patient on his side. The sagittal plane of the body should be parallel, and the frontal plane should be perpendicular to the plane of the table. Hands are laid back as much as possible. Cassette size 24X30 cm is located along the table, its upper edge is 3-4 cm above the jugular notch of the sternum. The radiation beam is directed vertically tangentially to the body of the sternum to the center of the cassette (Fig. 492).
The picture can be taken in the vertical position of the patient. In this case, the relationship between the sternum, the central beam of x-ray radiation and the cassette does not change (Fig. 493).
Rice. 492. Laying for radiography of the sternum in the lateral projection in a horizontal position on the side.
a - the position of the patient; 6 is a schematic representation of the relationship between the central x-ray beam, the region of interest and the cassette.
Rice. 495. Tomogram of the body of the sternum in direct projection.
Informative picture. The lateral view of the sternum clearly shows the anterior and posterior surfaces of the sternum. The sternum has the appearance of a convex anterior plate 1.5-2 cm wide. Front and back, it is delimited by a clear strip of the cortical layer. Usually, the junction of the sternum handle with its body (handle-sternal synchondrosis) is clearly visible, which has the form of a narrow transverse band of enlightenment with even contours, located on the border of the upper and middle thirds of the bone. With fractures of the sternum in such pictures, the displacement of bone fragments anteriorly or posteriorly is clearly defined (Fig. 494).
STERNUM TOMOGRAPHY
In the presence of clinical indications (mainly in order to identify small foci of destruction and damage), they resort to a layered study (tomo-, sonography of the sternum) in direct and lateral projections.
On layered images, as a rule, the structure of the studied sternum is clearly displayed (Fig. 495). The anatomical landmarks used in this case are given in Table. eighteen.
IS TABLE |
||||
Landmarks used |
||||
with tomography of the sternum (according to |
||||
V. A. Sizov) |
||||
Field of study |
Landmarks |
Projection |
||
The handle of the sternum and sternum |
Jugular notch of the sternum: 0.5- |
straight front |
||
physical joints |
2 cm posterior |
|||
Body of sternum |
Anterior sternum: |
|||
xiphoid process |
0.5-1 cm posteriorly |
|||
Anterior surface of the xiphoid |
||||
Handle, body and xiphoid |
process: 0.5-1 cm posteriorly |
|||
Median plane: 2-2.5 cm in |
||||
eostok sternum |
||||
GENERAL PRINCIPLES OF LUNG X-RAY EXAMINATION
X-ray examination of the lungs is the most common type of X-ray examination. It is widely used for the purpose of diagnosing various diseases and injuries of the lungs, objective monitoring of the dynamics of the pathological process, as well as for the timely diagnosis of latent diseases (essentially, in the preclinical phase).
The main methods of X-ray examination of the lungs are radiography, fluoroscopy, verification and diagnostic fluorography (in the USSR, every adult person once every 2 years, and in some organized groups, verification fluorograms of the lungs are performed annually). In addition, if necessary, they resort to a number of special research methods (tomography, sonography, bronchography, angiography, etc.).
The effectiveness of X-ray examination in each case is largely determined by the information content of the images, which, in turn, largely depends on the observance of certain general principles of radiography methods and techniques.
Special preparation for radiography or other methods of obtaining a picture (fluorography, electroroentgenography, tomography, etc.), as a rule, is not required. It is only necessary to expose the chest. Sometimes shooting is carried out in underwear. In such cases, it is necessary to check whether there are buttons, pins, and other objects on it that can cause shadows to appear in the picture. In women, the transparency of the upper lung fields may be reduced by a thick tuft of hair. Therefore, they must be collected and strengthened so that their image does not overlap on the lungs.
Distinguish survey and aiming pictures of the lungs. The study, as a rule, begins with a survey radiography, which is usually performed in standard projections (front and side). Targeted shots are more often taken in atypical positions that are optimal for detecting
15 A. N. Kishkovsky and others.
As is known, the total blurring in radiography of the organs of the chest cavity depends mainly on the dynamic blurring. It is possible to completely eliminate the dynamic blur due to the pulsatory movements of the heart and large vessels only at shutter speeds of 0.02-0.03 s. Therefore, it is necessary to strive to take images of the lungs at minimum shutter speeds (no more than 0.1-0.15 s), using sufficiently powerful X-ray installations for this.
To eliminate pronounced projection distortions, it is advisable to shoot at a focal length of 1.5-2 m (teleroentgenography). This requirement is due to the fact that the chest of an adult is of considerable size: on average, the anteroposterior size is 21 cm, the frontal (width) is about 30 cm. Under such conditions, various anatomical structures (including pathological ones) can be at a considerable distance from the film, which causes a less clear image of their contours in the image compared to similar structures adjacent to the film. When shooting from a relatively short focal length (100 cm or less), the difference in image clarity of structures located at different distances from the image sensor will be especially noticeable, which can create a prerequisite for a diagnostic error.
However, an increase in the focal length is permissible only in cases where it does not lead to a significant increase in shutter speed (above 0.1-0.15 s).
Pictures of the lungs are usually performed on an average breath, with a held breath. However, in the presence of special indications (detection of small accumulations of gas or liquid in the pleural cavity, the performance of functional tests), they resort to shooting after forced expiration.
In addition to conventional radiographs, in clinical practice, it is often sought to obtain deliberately "hard", "superexposed" lung images. On such radiographs, the image of the elements of the pulmonary pattern is often lost, however, the structure of pathological shadows, the trachea, large bronchi, as well as the bronchi located in the infiltrate, are displayed more clearly. To obtain "hard" images, increase the voltage on the tube by 10-15 kV or the exposure by 1.5-2 times.
PLANTS FOR LUNG RADIOGRAPHY
IMAGE OF THE LUNGS
AT DIRECT FRONT PROJECTION
The purpose of the image is to study the condition of the lungs if any of their disease or damage is suspected.
Laying for taking a picture (Fig. 496, a, b). Usually the picture is taken
nyat in the position of the patient standing (or sitting, depending on the condition) at a special vertical rack. The patient presses his chest tightly against the cassette, slightly bending forward. It is very important that both halves of the chest fit evenly (symmetrically) against the cassette. With the aim of
Rice. 496. Laying for radiography of the lungs in a direct anterior projection in the position of the patient standing.
a - view from the side of the tube; b - side view.
the removal of the shoulder blades for the pulmonary fields, the hands are pressed to the hips, and the elbows are directed forward. In this case, the shoulders of the subject should be lowered. The head is straight. The chin is slightly raised, stretched forward and is in contact with the upper edge of the cassette or is at its level (if the cassette is inserted into the screening grill housing). The optimal size of the radiographic film is 35X35 cm. A film of 30X40 cm in size can be used. Depending on the technical parameters of the study, shooting is carried out with or without a screening grid. So, when the voltage on the tube is 60-65 kV, the grating is not used, and when X-raying with hard beams (115-120 kV), the use of a grating is necessary.
The cassette is installed in such a way that its upper edge is at the level of the body of the VII cervical vertebra. The central X-ray beam is directed to the center of the cassette along the midline of the patient's body to the region of the VI thoracic vertebra (the level of the lower angle of the scapula). Exposure is made after a shallow breath with a delayed breath. During the shooting, the patient should not strain.
Rice. 497. A snapshot of the lungs in a direct anterior projection
(a) and the diagram for this picture
5 - root of the right lung (arteries are shaded, the contours of the aenas are shown by dots); 6 - congur of the right mammary gland; 7- rib body; 8- joint of the tubercle of the rib; 9 - front contour of the rib; 10 - contour of the left mammary gland; 11-diaphragm circuit.
Informative picture. On the radiograph of the lungs in the anterior direct projection, in addition to the lung tissue that forms the so-called lung fields, the soft tissues of the chest, chest and mediastinal organs are displayed (Fig. 497, a, b). The lung fields are conventionally divided into upper, middle and lower sections. The first is located between the upper edge of the lung and the line passing along the lower edge of the anterior end of the II rib, the second - between this line and the line drawn along the lower edge of the anterior end of the IV rib, the third - occupies the rest of the lung to the diaphragm.
In addition to these departments, three zones are distinguished in the lungs: internal (radical), middle and external. The conditional boundaries between them pass along vertically directed, parallel lines, crossing the clavicle, respectively, the boundaries between its third
transcript
1 A. N. Kishkovsky, L. A. Tyutin
2 UDC BBK A11 A11 A. N. Kishkovsky Atlas of laying in X-ray studies / A. N. Kishkovsky, L. A. Tyutin M .: Book on Demand, p. ISBN ISBN Edition in Russian, designed by YOYO Media, 2012 Edition in Russian, digitized, Book on Demand, 2012
3 This book is a reprint of the original that we have created especially for you using our patented reprint and print-on-demand technologies. First, we scanned every page of the original of this rare book on professional equipment. Then, with the help of specially designed programs, we cleaned the image from spots, blots, and folds and tried to whiten and even out each page of the book. Unfortunately, some pages cannot be restored to their original state, and if they were difficult to read in the original, then even with digital restoration they cannot be improved. Of course, automated software processing of reprinted books is not the best solution for restoring the text in its original form, however, our goal is to return to the reader an exact copy of the book, which may be several centuries old. Therefore, we warn about possible errors in the restored reprint edition. The publication may be missing one or more pages of text, there may be indelible stains and blots, inscriptions in the margins or underlining in the text, unreadable fragments of text or page folds. It is up to you to buy or not to buy such publications, but we do our best to make rare and valuable books, recently lost and unfairly forgotten, once again become available to all readers.
5 X-RAY IMAGE AND ITS PROPERTIES MAIN PROPERTIES OF X-RAY IMAGE As already noted, an X-ray image is formed when an X-ray beam passes through the object under study, which has an uneven structure. In this case, the radiation beam on its way crosses many points, each of which, to one degree or another (according to the atomic mass, density and thickness), absorbs its energy. However, the total attenuation of the radiation intensity does not depend on the spatial arrangement of individual points absorbing it. This regularity is schematically presented in fig. 4. It is obvious that all points that cause in total the same attenuation of the X-ray beam, despite the different spatial arrangement in the object under study, are displayed on the same plane in the image taken in one projection in the form of shadows of the same intensity. This pattern indicates that the X-ray image is planar and summative. The summation and planar nature of the X-ray image can cause not only summation, but also subtraction (subtraction) of the shadows of the studied structures. So, if there are areas of both compaction and rarefaction in the path of X-ray radiation, then their increased absorption in the first case is compensated by the reduced absorption in the second (Fig. 5). Therefore, when examining in one projection, it is not always possible to distinguish true compaction or rarefaction in the image of one or another organ from summation or, conversely, subtraction of shadows located along the X-ray beam. This implies a very important rule of X-ray examination: in order to obtain a differentiated image of all the anatomical structures of the study area, one should strive to take pictures in at least two (preferably three) mutually perpendicular projections: direct, lateral and axial (axial) or resort to targeted shooting by turning the patient behind the screen of the translucent device (Fig. 6). It is known that X-ray radiation propagates from the place of its formation (the focus of the emitter anode) in the form of a divergent beam. As a result, the x-ray image is always magnified. The degree of projection magnification depends on the spatial relationship between the X-ray tube, the object under study and the image receptor. This dependence is expressed as follows. At a constant distance from the object to the image receiver, the smaller the distance from the focus of the tube to the object under study, the more pronounced the projection magnification. As the focal length increases, the size of the X-ray image decreases and approaches the true size (Fig. 7). The opposite pattern is observed with an increase in the “image-receiving object” distance (Fig. 8). With a significant distance of the object under study from the radiographic film or other image receptor, the image size of its details significantly exceeds their true dimensions.
6 10 METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE Fig. 4. Identical summary image of several points on the image with different spatial arrangement of them in the object under study (according to V.I. Feoktistov). Rice. 5. The effect of summation (a) and subtraction (b) of shadows. The projection magnification of the x-ray image in each particular case can be easily calculated by dividing the distance "the focus of the image receiver" by the distance "the focus of the tube the object under study". If these distances are equal, then the projection increase is practically absent. However, in practice, there is always some distance between the object under study and the X-ray film, which causes the projection magnification of the X-ray image. In this case, it should be borne in mind that when shooting the same anatomical region, its various structures will be at different distances from the focus of the tube and the image receiver. For example, in a direct anterior chest x-ray, the anterior ribs will be less magnified than the posterior ones. The quantitative dependence of the projection magnification of the image of the structures of the object under study (in %) on the “film tube focus” distance (RFTP) and the distance from these structures to the film is shown in Table. 1 [Sokolov V. M., 1979].
7 X-RAY IMAGE AND ITS PROPERTIES 11 Pic. 6. X-ray examination performed in two mutually perpendicular projections. and the summation; 6 separate image of shadows of dense structures. Rice. Fig. 7. Dependence between the focus distance of the object tube and the projection magnification of the x-ray image. As the focal length increases, the projection magnification of the x-ray image decreases. Rice. 8. Dependence between the distance of the image receiver object and the projection magnification of the x-ray image. With increasing distance from the object to the image receiver, the projection magnification of the X-ray image increases.
8 12 METHODOLOGY AND TECHNIQUE OF OBTAINING X-RAY IMAGE TABLE 1 Dependence of the projection magnification of the structures of the object under study (in %) on RFTP and the distance from these structures to the RFTP film, cm .7 2.6 2.2 2.0 1.6 1.4 1.2 1.0 8.7 6.6 6.0 5.6 5.2 4.6 4.2 3.3 2.7 2.3 2.0 13.6 10.2 9.4 8.7 8.1 7.1 6.4 5.0 4.2 3.6 3.9 11.9 11.1 9.8 8, 7 6.8 5.6 4.8 4.2 16.6 15.4 14.3 12.5 11.1 8.7 7.1 6.0 5.2 42.8 30.0 27.2 25 .0 23.0 20.0 17.6 12.6 11.1 9.3 8.1 66.6 44.4 40.0 36.4 33.3 28.5 25.0 19.0 15.4 12.9 11.5 56.6 50.0 45.4 38.4 33.3 25.0 20.0 16.6 14.7 60.0 50.0 42.8 31.6 25.0 20, 0 17.6 233.3 116.5 77.7 63.6 53.8 38.8 30.0 25.0 21.2 400.0 160.0 133.3 114.2 100.0 80.0 66 .6 47.0 36.4 29.6 25.0 9. Change in the edge-forming areas of the skull with increasing focal length. ab edge-forming points at the minimum focal length (fi); aib] edge-forming points at a significant focal length (b). From the foregoing, it is obvious that in those cases where it is necessary that the size of the x-ray image be close to the true, it is necessary to bring the object under study as close as possible to the cassette or translucent screen and remove the tube to the maximum possible distance. When the latter condition is met, it is necessary to take into account the power of the X-ray diagnostic apparatus, since the radiation intensity varies inversely with the square of the distance. Usually, in practical work, the focal length is increased to a maximum of 2 2.5 m (teleroentgenography). Under these conditions, the projection magnification of the x-ray image is minimal. For example, an increase in the transverse size of the heart when shooting in a direct anterior projection will be only 1 2 mm (depending on the distance from the film). In practical work, it is also necessary to take into account the following circumstance: when the RFTP changes, various parts of it take part in the formation of the contours of the shadow of the object under study. So, for example, in the pictures of the skull in direct anterior projection
9 X-RAY IMAGE AND ITS PROPERTIES 13 Pic. 10, Projection reduction of the x-ray image of linear structures depending on their location in relation to the central x-ray beam. Rice. 11. Image of a planar formation with the direction of the central X-ray beam perpendicular to it and to the image detector (a) and with the direction of the central beam along the planar formation (b). at a minimum focal length, the edge-forming areas are those located closer to the tube, and at a significant RFTP, those located closer to the image receiver (Fig. 9). Despite the fact that the X-ray image is in principle always enlarged, under certain conditions, a projection reduction of the object under study is observed. Typically, such a reduction concerns the image of planar formations or structures that have a linear, oblong shape (bronchi, vessels), if their main axis is not parallel to the plane of the image receiver and not perpendicular to the central X-ray beam (Fig. 10). It is obvious that the shadows of the bronchi, as well as blood vessels or any other objects of an oblong shape, have a maximum size in cases where their main axis (in a parallel projection) is perpendicular to the direction of the central beam. As the angle formed by the central beam and the length of the object under study decreases or increases,
10 14 METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE Fig. 12. Distortion of the image of the ball during X-ray examination with an oblique beam (a) or with an oblique location (in relation to the central beam) of the image receiver (b). Rice. 13. "Normal" image of spherical (a) and oblong (b) objects in the study in an oblique projection. The position of the tube and cassette is changed so that the central X-ray beam passes through the center of the object perpendicular to the cassette. The longitudinal axis of the oblong object runs parallel to the plane of the cassette. the size of the shadow of the latter gradually decreases. In the orthograde projection (along the central beam), a blood-filled vessel, like any linear formation, is displayed as a dotted homogeneous shadow, while the bronchus looks like a ring. The combination of such shadows is usually determined on the pictures or on the screen of the X-ray machine when transilluminating the lungs. In contrast to the shadows of other anatomical structures (compacted lymph nodes, dense focal shadows), when turning, they become linear. Similarly, the formation of an x-ray image of planar formations occurs (in particular, with interlobar pleurisy). The maximum dimensions of the shadow of a planar formation are
11 X-RAY IMAGE AND ITS PROPERTIES in those cases when the central radiation beam is directed perpendicular to the plane and film under study. If it passes along a planar formation (orthograde projection), then this formation is displayed on the image or on the screen as an intense linear shadow (Fig. 11). It should be borne in mind that in the variants considered, we proceeded from the fact that the central X-ray beam passes through the center of the object under study and is directed to the center of the film (screen) at a right angle to its surface. This is usually sought in radiodiagnosis. However, in practical work, the object under study is often located at some distance from the central beam, or the film cassette or screen is not located at a right angle to it (oblique projection). In such cases, due to the uneven increase in individual segments of the object, its image is deformed. So, bodies of spherical shape are stretched mainly in one direction and acquire the shape of an oval (Fig. 12). Such distortions are most often encountered when examining certain joints (head of the femur and humerus), as well as when performing intraoral dental imaging. To reduce projection distortions in each particular case, it is necessary to achieve optimal spatial relationships between the object under study, the image receiver, and the central beam. To do this, the object is installed parallel to the film (screen) and through its central section and perpendicular to the film, the central X-ray beam is directed. If for one reason or another (forced position of the patient, peculiarity of the structure of the anatomical region) it is not possible to give the object the necessary position, then normal shooting conditions are achieved by correspondingly changing the position of the focus of the tube and the image receiver of the cassette (without changing the position of the patient), as shown in rice. 13. INTENSITY OF THE SHADOWS OF THE X-RAY IMAGE The intensity of the shadow of a particular anatomical structure depends on its "radio transparency", i.e. the ability to absorb x-rays. This ability, as already mentioned, is determined by the atomic composition, density and thickness of the object under study. The heavier the chemical elements that make up the anatomical structures, the more they absorb X-rays. A similar relationship exists between the density of the objects under study and their X-ray transmission: the greater the density of the object under study, the more intense its shadow. That is why an x-ray examination usually easily identifies metal foreign bodies and it is very difficult to search for foreign bodies that have a low density (wood, various types of plastic, aluminum, glass, etc.). Depending on the density, it is customary to distinguish 4 degrees of transparency of media: air, soft tissue, bone and metal. Thus
12 16 METHOD AND TECHNIQUE OF OBTAINING X-RAY IMAGE It is obvious that when analyzing an X-ray image, which is a combination of shadows of different intensity, it is necessary to take into account the chemical composition and density of the studied anatomical structures. In modern X-ray diagnostic complexes that allow the use of computer technology (computed tomography), it is possible to confidently determine the nature of tissues (fat, muscle, cartilage, etc.) by the absorption coefficient in normal and pathological conditions (soft tissue neoplasm; cyst containing fluid, etc.). ). However, under normal conditions, it should be borne in mind that most tissues of the human body differ slightly from each other in their atomic composition and density. So, muscles, parenchymal organs, brain, blood, lymph, nerves, various soft tissue pathological formations (tumors, inflammatory granulomas), as well as pathological fluids (exudate, transudate) have almost the same “radio transparency”. Therefore, a change in its thickness often has a decisive influence on the intensity of the shadow of a particular anatomical structure. It is known, in particular, that with an increase in body thickness in arithmetic progression, the X-ray beam behind the object (output dose) decreases exponentially, and even slight fluctuations in the thickness of the structures under study can significantly change the intensity of their shadows. As seen in fig. 14, when shooting an object that has the shape of a trihedral prism (for example, the pyramid of the temporal bone), the shadow areas corresponding to the maximum thickness of the object have the highest intensity. So, if the central beam is directed perpendicular to one of the sides of the base of the prism, then the intensity of the shadow will be maximum in the central section. In the direction towards the periphery, its intensity gradually decreases, which fully reflects the change in the thickness of the tissues located in the path of the X-ray beam (Fig. 14, a). If, however, the prism is rotated (Fig. 14, b) so that the central beam is directed tangentially to any side of the prism, then the maximum intensity will have the edge section of the shadow corresponding to the maximum (in this projection) thickness of the object. Similarly, the intensity of shadows that have a linear or oblong shape increases in cases where the direction of their main axis coincides with the direction of the central beam (orthograde projection). When examining homogeneous objects that have a round or cylindrical shape (heart, large vessels, tumor), the thickness of the tissues along the X-ray beam changes very slightly. Therefore, the shadow of the object under study is almost homogeneous (Fig. 14, c). If a spherical or cylindrical anatomical formation has a dense wall and is hollow, then the X-ray beam in the peripheral sections passes through a larger volume of tissues, which causes the appearance of more intense blackout areas in the peripheral sections of the image of the object under study (Fig. 14, d). These are the so-called "edge borders". Such shadows, in particular, are observed in the study of tubular bones, vessels with partially or completely calcified walls, cavities with dense walls, etc. It should be borne in mind that in practical work for the differentiated perception of each specific shadow,
13 X-RAY IMAGE AND ITS PROPERTIES 17 Pic. 14. Schematic representation of the intensity of the shadows of various objects, depending on their shape, position and structure. a, b trihedral prism; into a solid cylinder; g hollow cylinder, has not absolute intensity, but contrast, i.e., the difference in the intensity of the given and surrounding shadows. At the same time, physical and technical factors that affect the contrast of the image become important: radiation energy, exposure, the presence of a screening grating, raster efficiency, the presence of intensifying screens, etc. Incorrectly selected technical conditions (excessive voltage on the tube, too high or, conversely, insufficient exposure, low raster efficiency), as well as errors in the photochemical processing of films, reduce the image contrast and thus have a negative effect on the differentiated detection of individual shadows and an objective assessment of their intensity. FACTORS DETERMINING THE INFORMATIVITY OF THE X-RAY IMAGE The informativeness of the X-ray image is estimated by the amount of useful diagnostic information that the doctor receives when examining the image. Ultimately, it is characterized by the visibility of the details of the object under study on the photographs or on a translucent screen. From a technical point of view, the quality of an image is determined by its optical density, contrast and sharpness. Optical density. As is known, the action of X-ray radiation on the photosensitive layer of an X-ray film causes changes in it, which, after appropriate processing, appear in the form of blackening. The intensity of blackening depends on the dose of X-ray radiation absorbed by the photosensitive layer of the film. Usually, the maximum blackening is observed in those areas of the film that are exposed to a direct beam of radiation passing by the object under study. The intensity of blackening of other sections of the film depends on the nature of the tissues (their density and thickness) located in the path of the X-ray beam. For an objective assessment of the degree of blackening of the developed X-ray film, the concept of "optical density" was introduced.
14 18 METHODOLOGY AND TECHNIQUE OF OBTAINING X-RAY IMAGE The optical density of film blackening is characterized by the attenuation of the light passing through the negative. To quantify the optical density, it is customary to use decimal logarithms. If the intensity of the light incident on the film is denoted as / 0, and the intensity of the light transmitted through it is 1, then the optical blackening density (S) can be calculated by the formula: Photographic blackening is taken as the unit of optical density, when passing through which the luminous flux is attenuated by 10 times (Ig 10 = 1). Obviously, if the film transmits 0.01 part of the incident light, then the blackening density is 2 (Ig 100 = 2). It has been established that the visibility of X-ray image details can be optimal only at well-defined, average values of optical densities. Excessive optical density, as well as insufficient blackening of the film, is accompanied by a decrease in the visibility of image details and the loss of diagnostic information. In a good quality chest x-ray, the nearly transparent shadow of the heart has an optical density of 0.1 0.2 and a black background of 2.5. For a normal eye, the optimal optical density ranges from 0.5 to 1.3. This means that in this range of optical densities, the eye can well detect even slight differences in the degree of blackening. The finest details of the image differ within blackening 0.7 0.9 [Katsman A. Ya., 1957]. As already noted, the optical density of the blackening of the x-ray film depends on the magnitude of the absorbed dose of x-ray radiation. This dependence for each photosensitive material can be expressed using the so-called characteristic curve (Fig. 15). Typically, such a curve is drawn on a logarithmic scale: logarithms of doses are plotted along the horizontal axis; along the vertical values of optical densities (blackening logarithms). The characteristic curve has a typical shape, which allows you to select 5 sections. The initial section (up to point A), almost parallel to the horizontal axis, corresponds to the veil zone. This is a slight blackening that inevitably occurs on the film when exposed to very low doses of radiation or even without radiation as a result of the interaction of a part of the silver halide crystals with the developer. Point A represents the blackening threshold and corresponds to the dose required to induce visually distinct blackening. Segment AB corresponds to the underexposure zone. Densities of blackening here increase slowly at first, then rapidly. In other words, the nature of the curve (gradual increase in steepness) of this section indicates an increasing increase in optical densities. The BV section has a rectilinear shape. Here, an almost proportional dependence of the density of blackening on the logarithm of the dose is observed. This is the so-called zone of normal exposures. Finally, the upper portion of the SH curve corresponds to the overexposure zone. Here, as well as in the AB section, there is no proportional relationship between the optical density and the radiation dose absorbed by the photosensitive layer. As a result, distortions occur in the transmission of the x-ray image. From what has been said, it is obvious that in practical work it is necessary to use such technical conditions of the film that would provide
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The distance from the lens to the actual image of the object is n =.5 times the focal length of the lens. Find the magnification G with which the object is depicted .. The distance from the object to the collecting
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Block 11. Optics (geometric and physical Lecture 11.1 Geometric optics. 11.1.1 Laws of light propagation. If light propagates in a homogeneous medium, it propagates in a straight line. This
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96 GEOMETRIC OPTICS Task 1. Choose the correct answer: 1. The proof of the rectilinear propagation of light is, in particular, the phenomenon ... a) interference of light; b) shadow formation; c) diffraction
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3. Tsesler L.B. Small-sized ultrasonic device "Quartz-5" for measuring the wall thickness of parts of complex shape. In the book: Problems of non-destructive testing. K: Nauka, 1973. 113-117s. 4. Grebennik V.S. Physical
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Optics Optics is a branch of physics that studies the laws of light phenomena, the nature of light and its interaction with matter. A light ray is a line along which light travels. Law
GEOMETRIC OPTICS Many simple optical phenomena, such as the appearance of shadows and the formation of images in optical instruments, can be explained on the basis of the laws of geometrical
Exam Polarizers based on Nicol and Wollaston prisms Nicol are made from a natural crystal of Icelandic spar, which has the shape of a rhombohedron:
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