TOMOGRAPHY

From Big Medical Encyclopedia

TOMOGRAFYYa (Greek tomos a piece, a layer - j-graphd to write, represent; synonym: layer-by-layer X-ray inspection, a laminografiya, a stratigraphy) — the method of X-ray inspection consisting in obtaining the shadow image of the separate layers of the studied object lying at a different depth.

For the first time idea layer-by-layer rentge-nol. researches were put forward in 1921 by the French scientist of A. Bocage. Practical development of this method was carried out in 1930 in Italy by A. Vallebona, in 1931 in Holland Tsidzes de Plantom (V. Ziedses des Plantes), in 1935 in the USSR V. I. Feoktistov and in Germany G. Grossmann. In a crust, time of T. — one of widespread methods of X-ray inspection (see).

T. make by means of special X-ray diagnostic devices — tomographs (fig. 1). The tomograph consists of the x-ray feeding device, a radiator, the receiver of radiation (the cartridge with a X-ray intensifying screen and a film or a selenic plate), devices for fixing of the patient, and also the mechanism for synchronous movement of a radiator and the receiver or the patient and the receiver of radiation.



Fig. 1. Diagrammatic representation of the horizontal tomograph: 1 — a radiator

(X-ray tube); 2 — a pendulum (the core fastening a radiator and the receiver of radiation); z — a rack for fixing of an axis of swing; 4 — the operating console; 5 — the motor drive (the mechanism for synchronous movement of a radiator and the receiver of radiation); 6 — the receiver of radiation; 7 — a table.


At the heart of T, the principle of synchronous movement in space lies during x-ray shooting of two or three components of system a X-ray emitter — the studied object — the receiver of radiation. Preferential distribution was gained by T., at a cut the studied object is not mobile, and a X-ray tube and the cartridge with



Fig. 2. The diagrammatic representation of movement of mobile parts in linear and circular tomographs: 1 — a radiator (X-ray tube); 2 — the receiver of radiation; 3 — the allocated layer; shooters designated a trajectory of the movement of mobile parts.


a film move in opposite directions. At the synchronous movement of a radiator and the receiver and turn of a bunch of radiation concerning the certain center lying at the set depth of the studied object there is «spreading» of shadow images of the details located above and lower than the plane in a cut this center lies. Such «spreading» on a x-ray film is resulted by a sharp image of the details which are in the plane of a cut in the depth of the studied object.

T. classify by orientation of the studied layers of rather longitudinal axis of a body of the patient (longitudinal, cross, panoramic T.), on a trajectory of the movement of system a radiator — the receiver (linear, nonlinear, combined), by space position of the patient during the research (horizontal, vertical, inclined). Respectively distinguish also types of tomographs: about

submultiple, cross and panoramic. The last provide the image of layers, shaped curved surfaces. Tomographs happen also horizontal, vertical or universal (rotary). On the nature of movement of mobile parts distinguish the linear, nonlinear, circular and combined tomographs (fig. 2).

Key parameters of T.


the size of a tilt angle and a trajectory of the movement of a radiator are determining thickness in ydo l of a mute layer and efficiency «a razmazyva a niya» the disturbing shadows. Optimum «spreading» of the disturbing shadows is reached by movement of system a radiator — the receiver on difficult curvilinear trajectories in the form of a circle, an ellipse or a spiral. The greatest distribution in rentgenol. to practice received the tomographs providing rectilinear «spreading». They allow to receive horizontal longitudinal linear tomograms by means of a support of pictures and a table of X-ray diagnostic stationary devices of the general purpose equipped with the special mechanism for movement of a radiator and the cartridge. Such mechanical prefixes supply all domestic stationary X-ray diagnostic devices and the majority foreign (see. X-ray apparatus), belong also domestic M-1, prefix tomograph for a longitudinal tomography of Ts-1402 and Ts-1404 To linear tomographs. Common fault of horizontal tomographs is the impossibility to conduct researches in vertical and inclined provisions of the patient. This defect is eliminated in universal tomographs, to the Crimea the domestic Ts-1730 tomograph giving linear «spreading» belongs. In the vertical cross Ts-1875 tomograph synchronously move a chair with the sitting patient and the receiver with a film. Use panoramic nonlinear tomographs to receiving panoramic exposures of jaws and other parts of a skull, to the Crimea the domestic Ts-5045 tomograph, and also OP-5, OP-6 orthopan-tomographs (Finland), etc. belong. The horizontal panoramic OP-6 tomograph, the most perfect of this class of tomographs, has 5 programs for receiving panoramic exposures of jaws, cervical vertebrae, Highmore's bosoms, a midface and eye-sockets.

Main characteristic of T., op r to food of l yayushche y d news agency gn wasps of t iches I forge

informational content of a method, thickness of the allocated layer (cut), i.e. distance between two parallel planes of section of a body of interest is, in a zone to-rogo elements of an object are displayed subjectively sharply. The term «thickness of the allocated layer» is conditional since includes subjective criterion — assessment of sharpness of the image. The tilt angle of a radiator is considered the main technical factor determining thickness of the allocated layer. In rentgenol. practice can allocate 4 layers of various thickness: superthick

(a tilt angle of a radiator 5 — 9 °),


thick (a tilt angle 10 — 20®), average (a tilt angle 25 — 30 °) and thin (a tilt angle 35 — 50 °). The choice of a layer of necessary thickness depends on character of a body of interest and specific diagnostic objectives. Thickness of a layer is determined also by other factors: a ratio of distances between a X-ray emitter, the receiver and an object of a research, the volume, density and dimensional orientation of the structural elements of an object which are especially located in the studied layer and near it. So, the tomographic effect will decrease with increase in density and size of anatomic details, at coincidence of extent of structural elements of an object (bronchial tubes, vessels, bone beams, etc.) with the direction of the movement of a radiator. Thus, the real tomographic layer is not limited by a plane surface, and has more irregular shape. Diagnostic value T. depends also on quality of the tomographic image. It shall have the optimum optical density and the minimum unsharpness.

For obtaining the simultaneous image of several layers of the studied object the so-called simultaneous T is offered. with use of the special cartridge, in a cut at a certain distance, separated from each other by laying, there are several films placed between X-ray intensifying screens with the increasing degree of a luminescence. Thus it is possible to offset loss of intensity of x-ray emission owing to its absorption in X-ray intensifying screens.

For upgrading of T. special X-ray Expos-nometry are offered. The disturbing shadows on the tomogram can be eliminated with method of subtraction (see). For objectification of these T. use densitometry (see). The analysis of fine details of an object is made by means of direct blowup. T. it is possible to combine with other methods rentgenol. researches: a bronchography (see) — tomo-

a bronchography, an angiography (see) — a tomoangiografiya, fluorography (see) — a tomoflyuorografiya, a kimogra-fiya (see) — a tomokimografiya, an electrox-ray analysis (see) etc.

More often than T. apply at diseases of lungs. Depending on research problems of T. lungs carry out at various tilt angles of a radiator: from minimum (5 — 9 °) — a zonografiya to maximum (40 — 50 °) — a thin layer

tomography. The plane and level of the allocated layer choose on the basis of the preliminary analysis


of Fig. 3. The tomogram of a thorax (a direct projection) at the abscessing pneumonia of an upper share of the left lung: the arrow

specified a cavity of disintegration with the sequester.

roentgenograms of a thorax. At the same time T. it is possible to make in frontal (direct tomograms), sagittal (side tomograms), or a slanting, non-standard projection. When patol. education is localized in the central sites of a lung (a kernel of a lung) or its peripheral departments (a raincoat of a lung), it is necessary to apply T. in direct and side projections. At the same time the level of a layer-by-layer research is chosen proceeding from the sizes patol. educations. At localization patol. process in sites easy, inconvenient for rentgenol. researches (a top, near a pulmonary furrow of a thorax, at the basis of a lung), T. make in a slanting projection.

On tomograms details patol are displayed. process, indistinctly differentiable or hidden owing to superposition in a survey picture. So, at T. tubercular cavities, usually indiscernible among densely located focal and extensive infiltrative changes, covered with a shadow massive pleural shvart, and also normal anatomic formations of a thorax — edges, clavicles, bodies of a mediastinum can be revealed. On tomograms cavities of disintegration during the abscessing (fig. 3) clearly are visible. At a research such patol. educations in lungs as peripheral cancer, a tuberkuloma, a cyst, etc., on tomograms it is possible to find important differential diagnostic characters — small cavities of disintegration, calcificats, the knotty nature of education and also to study a condition of surrounding pulmonary fabric.

In layer-by-layer pictures big detailing of the pulmonary drawing is possible that it matters at inspection of patients with developments of stagnation in lungs and diffusion changes of inflammatory character. For identification of metastasises of malignant tumors, small, invisible on the survey roentgenogram, in lungs use so-called continuous, or total, T. lungs, at a cut carry out a series of tomograms through all thickness of a thorax with an interval of 1 — 2 cm.

At a research of a trachea and large bronchial tubes of T. make in a characteristic frontal projection. T. segmental and subsegmental bronchi carry out in a slanting projection. At the same time the patient is stacked in different provisions according to certain schemes. Tomographic studying of a gleam of bronchial tubes and bronchial walls plays a large role at recognition of tumors and inflammatory processes in easy, foreign bodys in bronchial tubes, etc. A tomography — an obligatory component rentgenol. researches intrathoracic limf, nodes at patients with a tubercular bronchadenitis and malignant tumors of lungs.

T. is a valuable method rentgenol. researches of a throat, allowing not only to study a pestilence foul. structure of this body, but also odnovrekhmenno to estimate elasticity of anatomic elements, first of all phonatory bands. T. throats make in a direct projection, the allocated layer is located

2 — 3 cm more deeply than the most acting point of a thyroid cartilage. Usually carry out a series of tomograms at various functional trials: during a long breath, at phonation of a sound «and», at an expiratory natuzhivaniye (see Valjsaljva experience). T. throats use not only for diagnosis of malignant tumors (fig. 4), but also for control of efficiency of radiation therapy.


Fig. 4. The tomogram of a throat (a direct projection) at throat cancer: the arrow specified tumoral infiltration of phonatory bands.,


Fig. 5. Tomogram of the left half of a thorax (direct projection): the arrow specified calcification of a fibrous ring of the left atrioventricular opening.

T. allows to solve a number of problems in cardiology. At rheumatic heart diseases of T. helps to reveal signs of increase in separate cameras of heart, first of all the left auricle, endocardiac calcifications of valves of heart, fibrous rings (fig. 5), endocardiac blood clots, etc., to study a condition of a small circle of blood circulation. A lot of additional information is supplied by T. at inspection of patients with inborn heart diseases. By means of T. specify diagnosis of aortic aneurysms and a pulmonary trunk, find the place of narrowing (coarctation) of an aorta, define area of amputation of a trunk and pulmonary arteries at their thromboembolism.

T. considerably expands diagnostic opportunities rentgenol. researches of zhelchevydelitelny system. In layer-by-layer pictures it is possible to reveal the stones which are not seen on holetsistogramma and holegramma, tumors and inflammatory strictures.

In urology of T. is an obligatory component of infusional urography (see) — a nefrotomografiya, edges allows to reveal the defects of a renal parenchyma, small on volume, caused by tumors, cysts or sclerous process. On nefrotomogramma the rentgeno-grammetriya (see) important in diagnosis of pyelonephritis, anomalies of development, a renovascular hypertension can be more precisely made.

Range of application of T. bones and joints it is limited generally to a research of a skull and backbone, is more rare than other sites of a skeleton. On tomograms it is possible to find the details of a structure of bones which are not seen on usual roentgenograms, their relationship, and also a row rentgenol. symptoms: osteosclerosis, osteonecrosis, destruction, disturbance of integrity of a bone, patol. reorganization, etc. (fig. 6).

For receiving more sharp image of nek-ry bodies of T. combine with artificial contrasting of surrounding space gas. So, T. a thymus (fig. 7) make in the conditions of


Fig. 6. The tomogram of adnexal bosoms of a nose (a direct projection) at a malignant tumor of the left Highmore's bosom: homogeneous intensive blackout of a bosom, destruction of its roof and internal wall (it is specified by shooters).


Fig. 7. The tomogram of a thorax (the left side projection) in the conditions of a pneumomediastinum — a pnevmomediastinotomogra-fiya: the arrow specified the increased thymus.

a pneumomediastinum (see), a pancreas, kidneys and adrenal glands — in the conditions of a pneumoretroperitoneum (see), intracranial tumors — at a pneumoencephalography (see).

Despite development of other methods layer-by-layer rentgenol. researches (computer x-ray, emission, ultrasonic tomography), classical x-ray T. did not lose the value and it is still widely applied in a complex diagnostic rentgenol. researches and during the planning of radiation therapy.

See also Tomography a computer, Emission computer tomography.

Bibliography: And d at r and with at l about in D. M. and Nikishin of K. E. Tomografiya of a normal skull, Tashkent, 1966; Of l hell y sh B. Tomografiya in clinical practice, the lane with polsk., Warsaw, 1965, bibliogr.; To and and D. V., Perelman V. M. and Segal A. S. Zonogra-fiya Kidneys, Vestn. rentgenol. and radio-gramophones., No. 2, page 59, 1977; Kevesh L. E. and Lindenbraten L. D. Layer-by-layer X-ray inspection of heart and large vessels of a chest cavity, in the same place, No. 3, page 19, 1961; Kovac F. and e-@ yo to 3. X-ray anatomic bases of a research of lungs, the lane with it is mute., Budapest, 1962; To about r about l yu to I. P. Zonografiya of lungs, M., 1984; Corot I. P.'s hatch, etc. The directed (selection) zonografiya of a tracheobronchial tree, Vestn. rentgenol. and radio-gramophones., No. 1, e. 13, 1982; Lindenbraten L. D. and N and L. B minds. Methods of X-ray inspection of bodies and systems of the person, Tashkent, 1976; M and m and l I-e in R. M. Znacheniye of a zonografiya and bron-hozonografiya in diagnosis of chronic nonspecific diseases of lungs, Vestn. rentgenol. and radio-gramophones., No. 4, page 57. 1979; P and l of e e in N. R., P and to and N I.Kh! and Borodulin V. I. Introduction to a clinical electrox-ray analysis, M., 1971; Rybakova N. I. and Kuznetsov S.A. To a question of a technique of a tomographic research of a bronchial tree, Vestn. rentgenol. and radio-gramophones., Ns 2, page 36, 1968; Technical means of radiodiagnosis, under the editorship of I. A. Peryoslegin, M., 1981; Hajj and G.'s dek and B from e in B. S. Tomografiya of bones, the lane with Bol, Sofia, 1959, bibliogr.; H i'k and E. G. r-dynes, Stoltser S. M. and F. A. Residents of Astrakhan. X-ray tomographic apparatus, M., 1976, bibliogr.; Es se of S. of Topographische Ausdeutung der Bronchien im Rontgenbild, Stuttgart, 1957, Bibliogr.; Evans J. A. Nephrotomography, Radiology, at. FROM, p. 483, 1974; W e s t r a D. Zonography, The narrow-angle tomography, Amsterdam, 1966, bibliogr.

I. P. Korolyuk; E. B. Kozlowski (tekhn.).,

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