From Big Medical Encyclopedia


(Greek tomos a piece, a layer - f grapho to write, represent; English computer, from armor. to consider computo, to calculate; synonym: an axial computer tomography, a computing x-ray tomography, a tomodensito-metriya) — the method of X-ray inspection consisting in circular raying of an object x-ray emission and the subsequent creation by means of the high-speed computer of the layer-by-layer image of this object.

Basic advantage Since before usual rentgenol. by methods of a research (see. X-ray inspection) is a possibility of gravity test of fabrics and environments of an organism by means of densitometry (see Rentge-nodensitometriya) that allows to differentiate thinly studied substrate, napr, the liquid and turned blood filled with liquid a cyst and a tumor, borders of hypostasis of fabrics, etc. The computer tomography gives the chance to establish localization and prevalence patol. process in body and different body tissues to track dynamics various patofizi-ol. processes to estimate results of treatment. Since allows to carry out a tonometriya of the studied objects during the planning of radiation therapy, to choose approaches and volume of an operative measure, to carry out a stereotaxic biopsy of intracranial tumors, etc.

The mathematical principles of a method were proved by Cormac (And. M of Cormack) in the 60th 20 century. The first official statement about use Since for a research of the head of the person is made Haunsfil-dom and Ambrous (G. Hounsfield, J. Ambrose) in 1972. The first computer tomograph for all body was created by R. Ledley in 1974. For development of a method of a computer tomography in 1979 Mr. to Haunsfildu and Cormac the Nobel Prize was awarded.

Since make by means of the computer tomographs having the scanner consisting of a source of x-ray emission, detectors, perceiving it and the system providing their movement; system of transformation of information registered by detectors; the specialized COMPUTER making images of calculation, necessary for creation, on the set algorithm; system of record and reproduction of the reconstructed images of interior of thin coats of an object in axial (cross) section.

Fig. 1. Schematic diagram of the device of the computer tomograph (a) and habit view of its x-ray part (b): 1 — a X-ray tube (shooters designated the direction of movement of a tube); 2 — a set of scintillation detectors; 3 — the layer of fabrics allocated on the computer tomogram; 4 — a frame in which the X-ray tube and detectors move; <5 — an opening in a frame for the patient; 6 — a table.

The scanner of the modern computer tomograph represents a circular frame, in a cut the rotating X-ray tube and numerous scintillation detectors (fig. 1) located a ring are established. In process Since the X-ray tube rotates around a motionless object (the explored area of a body of the person which is in a frame of the scanner), at the same time the posterior collimated pyramid of x-ray emission passes through the illuminated layer under different corners. During the passing of a bunch of radiation through fabrics of various density intensity of a bunch is weakened, it is registered detectors, data with to-rykh are transferred for processing to the COMPUTER. Various bodies and tissues of the person absorb x-ray emission in unequal degree, i.e. have various absorbtion coefficients. The COMPUTER establishes value of an absorbtion coefficient of x-ray emission for each point of the scanned layer. Gives results of difficult processing of all array of absorbtion coefficients in the illuminated layer of the COMPUTER in a conditional scale of integers (a scale of units of density of Haunsfild, or KT-units), at the same time the size of an absorbtion coefficient of x-ray emission is accepted by water equal to zero. The scale of a scale of density is chosen so that the fabrics which are contained in a human body and are Wednesdays in the range of conventional units from — 1000 (air) to + 1000 (bone). Density on a cut can be measured both in one point, and in the set area of any form; the histogram of density for a certain body, a profile of density along the set line in the chosen zone of a research can be constructed.

For visualization of the image the computer gives out on the screen of the television device of size of absorption of x-ray emission not only in conditional KT-units, but also will transform them to gradation of light brightness, and to great values of density there corresponds lighter image and vice versa. On the screen of the computer tomograph 16 — 20 gradation of the gray image perceived by a human eye at the same time are reproduced. However at a research of a layer (cut) special methods of densitometry (modulation of brightness) giving the chance to catch 0,5% distinction in an absorbtion coefficient can be used.

For receiving more sharp image of bodies is normal and patol. the centers at Since use an enhancement effect of contrast, to-ry arises at intravenous administration of iodinated radiopaque substance. Strengthening of contrast is connected with increase in an absorbtion coefficient of blood, accumulation of a contrast agent nek-ry tumors, etc.

Modern computer tomographs allow to allocate layers from 2 to 10 mm thick at a speed of scanning of one layer of 2 — 5 sec., with instant reproduction of the image in black-and-white or color option.

The image of the illuminated layer from the television screen can be made a copy by the camera of instant action «Polaroid» or is reproduced on a sheet x-ray film by means of the special device. The format of the image can be changed randomly.

The absorbed dose of x-ray emission at Since on average does not exceed 1 — 2 is glad (0,01 — 0,02 Gr). Depending on research problems and the sizes of the studied area make various quantity of axial cuts at different distance from each other. According to the data entered into computer memory in addition to the finished shooting axial, images side, direct, and sometimes and slanting paraaksi-alny projections of the studied area can be reconstructed.

Since carry out, as a rule, in position of the patient lying on spin. There are no contraindications to Since

Fig. 2. The computer tomogram of the head (cross section) is normal: 1 — bones of a skull; 2 — structures of a brain; 3 — a median crack of a brain and a crescent shoot of a meninx in it.

(except intolerance of X-ray contrast agents, use to-rykh optional). Patients easily postpone a research therefore it can be made in out-patient conditions, and also at seriously ill patients.

Advanced computer tomographs of the third and fourth generations give the chance to make Since both the head, and all body (a neck, bodies of a chest cavity, abdominal cavity, small pelvis, spinal cord, mammary glands, a backbone, bones and joints) and to solve complex diagnostic challenges. In the Soviet Union computer tomographs for a research of the head and all body are also created.

The greatest experience is accumulated at researches of the head (fig. 2). Since allows to receive on one cut the image of bones of a skull, structures of a brain, ventricular system of a brain, a subarachnoid space, etc. Since the heads make according to indications, after full a wedge, inspections of the patient with suspicion on defeat of c. N of page. In urgent cases (a craniocereberal injury, an acute disorder of cerebral circulation, etc.) the computer tomography is carried out right after survey of the doctor who established the condition of the patient menacing for life. Data Since in these conditions play a crucial role for establishment of indications to operation, its tactics or scheduling of the conservative actions directed to rescue of life of the patient. In all cases planned Since the heads it is a research make to pneumo-tsisternografii (see Pnevmoentsefalografiya), an encephalography (see), ventrikulografiya (see) and all types of a straight line and a retrograde cerebral angiography (see).

At a craniocereberal injury with the help Since reveal such posttraumatic changes as fractures of bones of the arch and base of skull, pneumocephalus, Epi - and subdural or intracerebral hematomas, local bruises of a brain, the phenomenon of local or generalized wet brain, dislocation of structures of a brain, etc. Repeated researches with use of tomo-densitometry allow to track evolution of contusional damages of a brain during the different periods of posttraumatic process, to define in a complex with data of clinical trials severity of a craniocereberal injury and its wedge, a form, to specify medical, including surgical, tactics. Since gives the chance to estimate a condition of ventricular system, tanks of the basis of a brain and other subshell spaces, and also compensatory opportunities of «reserve» intracranial spaces. Before implementation in a wedge, practice Since there were no methods allowing to watch visually dynamics of such complex process as wet brain.

Epidural hematomas on computer tomograms come to light as zones of the increased density biconvex, is more rare than a convexo-plane form; acute and subacute subdural hematomas — as the zones of the increased density of a crescent form extending to the most part or to all surface of a hemisphere (fig. 3). Upon termination of the acute period in rezul-

Fig. 3. The computer tomogram of the head (cross section) at a subdural hematoma: 1 — a crescent zone of the increased density (hematoma) in the left parencephalon, adjacent to a bone of a skull; 2 — a normal right side cerebral cavity; the left side ventricle because of a prelum is not differentiated by a hematoma.

Fig. 4. The computer tomogram of the head (cross section) at the bruise of a brain which is followed by hemorrhage: 1 — a zone of the increased density

in the left frontal lobe (hematoma); 2 and z — zones of the lowered density respectively around a hematoma and in the right frontal lobe, caused by local hypostasis in the field of a bruise of a brain.

the Tat of retraction of a clot of the streamed blood there is a gradual decrease in density of hematomas and absorbtion coefficients of the changed blood in a hematoma and the substance of a brain, next to it, become identical (an isodensity subdural hematoma). In these cases the diagnosis is based on secondary signs: a prelum of a side ventricle on the party of a hematoma, an obliteration or medial shift of subarachnoid konveksitalny furrows and dislocation of median structures of a brain. Chronic subdural hematomas can be the lowered or diverse density.

At bruises of a brain a picture on cuts of a polimorfn: depending on degree of hypostasis and existence of hemorrhages to the area of a bruise the centers of the lowered, increased or mixed density (fig. 4) can come to light.

Since allows to differentiate a heart attack and a hematencephalon. At the same time in the pool of blood supply of this or that vessel there can be a zone of density lowered (heart attack) or increased (hemorrhage). However for specification of level of occlusion or a stenozirovaniye of a vessel at a heart attack of a brain or establishment of the reason of hemorrhage the angiographic research is shown.

With the help Since it is possible to reveal (especially after contrasting) malformations of vessels (malfor-mation) and big meshotchaty aneurisms, to-rye have an appearance gyrose, roundish or an oval form of formations of the increased density.

At tumors of a brain with the help Since define the provision of a tumor, its relation to the vital formations of a brain, reveal a source of growth and prevalence of a tumor, degree of its operability, choose tactics of treatment and presumably establish gistol. structure of a tumor. At a tomodensitometriya of tumors of a brain allocate direct and indirect signs. Local change of density of substance of a brain belongs to straight lines, at the same time density of the center can be both is increased, and lowered (evenly or unevenly). A secondary sign is the so-called mass effect — the shift of structures of the centerline, a vascular texture, a prelum and deformation of side cerebral cavities, blockade of likvoroprovodyashchy ways, and also hydrocephaly, wet brain both near a tumor, and on a distance. Symptoms of intracerebral benign tumors are homogeneous or heterogeneous and granular decrease in density in limits patol. the center without change of density after administration of contrast medium or the homogeneous increase in density amplifying after administration of contrast medium. The centers of uneven density with a zone of low density (necrosis) in the center (fig. 5) are signs of a malignant tumor; this irregularity especially accurately comes to light after administration of contrast medium when there is a so-called crown effect — strengthening of density on borders of the center.

Meniignoma have an appearance of the center of the increased homogeneous density with accurate contours; sometimes in a tumor zones of disintegration, to ist, pet-are visible

to Riye. 5. The computer tomogram of the head (cross section) at an anaplastic astrocytoma in the left temporal area:

the arrow specified the ring-shaped zone of the increased density caused by existence of a tumor; in the center of a tumor density is lowered at the expense of a necrosis.

Fig. 6. The computer tomogram of the head (cross section) at an intra ventricular meningioma: 1 — the zone of sharply increased density with a clear boundary and extensive sites of calcification caused by existence of a tumor; 2 and 3 — the front and back horns of side ventricles expanded and deformed respectively.

rifikat (fig. 6), local wet brain is quite often expressed.

Metastasises of tumors in a brain on the tomogram look as the centers of uneven density which are well accumulating a contrast agent. It is quite often possible to find several metastasises at different stages of development (gomogenno dense nodes, nodes with signs of a necrosis opukholr1 inside) extensive hypostasis of white matter of a brain and the expressed mass effect, as a rule, comes to light.

Since allows to diagnose different types of inflammatory processes of a brain, napr, local meningoentsefalita,

to-rye on the tomogram have an appearance of the center of low density without clear boundary; the abscesses of a brain which are shown as formations of a round form with a zone of low density inside, with contours of the capsule of high density, edges considerably raises after contrasting (fig. 7); subdural empyemas, on the tomogram similar to hematomas, etc.

At parasitic diseases (cysticercosis, echinococcosis) on tomograms there are characteristic changes: an echinococcus has an appearance of the round center with a density close to density of water (cyst), various size, with the scarcely noticeable capsule having slightly increased density; at cysticercosis multiple come to light more often, single small knots of high density are more rare, at the same time symmetric or asymmetric hydrocephaly quite often is found.

Since plays a part in diagnosis of such diseases of c. N of cm as Alzheimer's disease (see Alzheimer a disease), a disease of Peak (see Peak a disease), a generalized leukodystrophy (see), an alcoholism (see an alcoholism), at to-rykh come to light symmetric zones of the lowered density in white matter of a brain, testimonial of atrophic process and hypoxemic injuries of a brain. At multiple sclerosis (see) on computer tomograms it is quite often possible to find the small centers with the reduced or increased density, shaped rings (a so-called plaque). At epilepsy, especially at so-called late forms of epilepsy, with the help Since quite often reveal volume intracranial processes. Since allows to diagnose surely orbital, kranioorbitalny and kraniofatsialny tumors. Important range of application Since is the research of c. N of page at children with malformations of a brain, hydrocephaly, a porencephalia, arachnoidal cysts, etc.

Fig. 7. The computer tomogram of the head (cross section) at abscess of a brain: 1 —

ring-shaped, with a clear boundary a zone of the increased density in the field of a pole of the left frontal lobe (the capsule of abscess); 2 ~ a zone of the lowered density (abscess cavity); 3 — the zone of uneven decrease in density of a brain caused by wet brain.

With the help kompyyuthe terny tomographs allowing to make researches of all body recognition of nek-ry diseases of a backbone and spinal cord is possible. Malformations of c. N of page at the spinal level, such as dip-lomiyeliya, diastematomyelia,

meningomyelocele and others (see. A spinal cord), well are defined at Since. Tumors of a spinal cord, especially extra silly woman lny and extramedullary (neurinoma, meningiomas), also as well as losses of intervertebral disks, are well visible at Since. Intramedullary

Fig. 8. The computer tomogram of a trunk (cross section at the level of VI of a chest vertebra) is normal: 1 — the ascending aorta; 2 — the descending aorta; 3 — a pulmonary trunk; 4 — the right pulmonary artery; 5 — a retrosternal fatty tissue; 6 — a vertebra.

tumors differ extremely difficult. Narrowing of the vertebral channel comes to light at Since it is much easier, than at a spondilografiya.

Since all body has the broad range of use. At a research of bodies of a thorax bodies of a mediastinum, the main vessels, heart (fig. 8), and also the lungs increased limf, nodes are well visible. In a front mediastinum the retrosternal craw having the accurate contours delimited from adjacent bodies and fabrics, the expressed capsule is easily diagnosed. At a malignancy its contours become indistinct, there is a shift and germination of the next bodies. Dermoid cysts on the computer tomogram look as the roundish educations delimited from other structures of a mediastinum and lungs. On the computer tomogram are differentiated a tumor of a mediastinum and aneurysm of chest department of an aorta, especially after intravenous administration of a contrast agent, a cut causes increase in an absorbtion coefficient in a gleam of aneurism. It is possible to see tumors of lungs and their metastasises in a mediastinum. Modern computer

Fig. 9. The computer tomogram of a trunk (cross section at the level of XII of a chest vertebra) is normal: 1 — a liver; 2 — a pancreas; 3 — a left kidney; 4 — a spleen; 5 — a ventral aorta; in — ■ the lower vena cava; 7 — a stomach; 8 — a vertebra; 9 — edges.

tomographs allow to distinguish nek-ry heart diseases. At bystry intravenous administration of 20 — 40 ml of a contrast agent on defect of contrasting on the computer tomogram it is possible to reveal a tumor of an auricle (myxoma), an exudate in a pericardium, blood clots in the left auricle, aneurisms of heart. Existence of a prefix of start of the tomograph from an ECG considerably expands diagnostic opportunities Since in this area.

At a research of abdominal organs and retroperitoneal space it is possible to receive the image of a spleen, liver, pancreas and kidneys (fig. 9). The ratio of density of a pancreas and the fabrics surrounding it allows to visualize all departments of gland. At the same time the tumor of a pancreas is determined not only by increase in body, but also by change of its density. At pancreatitis diffusion increase in gland or increase only in its head is noted. The differential diagnosis of chronic indurative pancreatitis and tumor of a pancreas is complicated. Cysts of a pancreas (fig. 10) are shown by increase in the size of body and existence of sites of decrease in density, and sometimes and calcifications. Since allows to define metastasises in a liver, to-rye can sometimes not have a clear boundary, and as if diffuzno infiltrirovat its fabric. Cysts of a liver (fig. 11) have an appearance of limited zones of the lowered density. At Since it is possible to distinguish fatty dystrophy of a liver and cirrhosis, diagnosis to-rykh is carried out densitometrically according to density of a parenchyma of a liver. The single vnut-ripechenochny formations of various nature located deeply in a liver are defined as patol. the center irrespective of whether they are a parasitic cyst, a benign tumor or abscess. Educations with a diameter from 5 — 10 mm are distinguished. The disseminated processes in a liver come to light, at the same time differential diagnosis of high-quality and malignant processes is complicated. Because of anatomic options the percent of false positive results at diffusion changes of a liver is especially high. The diagnostic value of a method increases during the use of strengthening of contrast.

Fig. 10. The computer tomogram of a trunk at the level of I lumbar vertebra at a cyst of a pancreas: 1 — a liver; 2 — a pancreas; z — a right kidney; 4 — a left kidney; 5 — a vertebra; in — muscles of a back; the arrow specified the zone of the lowered density in a pancreas having rounded shape and accurate contours (a cyst of a pancreas).

Fig. 11. The computer tomogram of a trunk, cross section at the level Of X of a chest vertebra at multiple cysts of a liver: 1 — a liver; 2 — basal departments of lungs; 3 ~ spleen; 4 — cavities of cysts; 5 — a vertebra.

Fig. 12. The computer tomogram of a trunk, cross section at the level of II of a lumbar vertebra at cholelithiasis: 1 — a liver; 2 — a gall bladder and which gleam the multiple centers of high density — stones of a gall bladder are visible; z — a right kidney; 4 — a left kidney; 5 — a vertebra.

With the help Since it is possible I bury to see a gall bladder, to reveal changes of its sizes and a form, expansion of the intra hepatic courses at disturbances of outflow of bile. Accurately shadows of concrements (fig. 12) are defined. The diagnosis of the disconnected

Fig. 13. The computer tomogram of a trunk (cross section at the level of IV of a lumbar vertebra) at aneurism of a ventral aorta: 1 — aneurism of a ventral aorta; 2 — a vertebra; about — a big lumbar muscle.

a gall bladder establish on the basis of increase in its sizes and a thickening of walls.

A research of kidneys more informatively at artificial contrasting. It is possible to define a tumor of a kidney or its cyst. In the latter case the center having low density comes to light.

Satisfactory results are received at Since retroperitoneal space. Lumbar muscles, fatty tissue, an aorta, the lower vena cava are normal accurately visible. In the presence patol. processes in retroperitoneal space of border of these structures are erased. In case of increase retroperitoneal limf, nodes it is not possible to see outlines of an aorta, the lower vena cava. At inflammatory processes in retroperitoneal cellulose contours of lumbar muscles are badly differentiated, subphrenic postoperative abscesses can be revealed. At diagnosis of aortic aneurysms (fig. 13) it is possible to see an aneurysmal bag, calcification or consolidation of a wall of an aorta, blood clots in a gleam of an aorta, anguishes of a vascular wall with existence of retroperitoneal hemorrhage. Apply a technique of strengthening of contrast to more accurate visualization.

The programs of calculations which are specially put in the COMPUTER of the latest computer tomographs allow to investigate along with obtaining images of anatomical structures and dynamic processes, i.e. to make also functional diagnosis. The most important premises of such dynamic scanning (with administration of radiopaque substances) is small time of measurements, big frequency of registration of images (to 21 shots in 1 min.), immediate obtaining the ready tomogram, a possibility of obtaining the chart density — time.

Use of data Since during the planning of radiation therapy plays a large role in increase in its efficiency at treatment of tumors of various localizations, first of all owing to increase in accuracy of volume localization and definition of contours of the target which is subject to radiation. The possibility of work with the COMPUTER in the dialogue mode allows in the presence of the programs of calculation of isodoses put in her memory to use data Since for the choice of optimum programs of radiation as for remote, and interstitial radiation therapy.

Since is a safe diagnostic method and does not give complications. Since as the high-informative method of a research does not exclude use of usual methods of clinical and X-ray inspection, it supplements their data and allows to obtain more complete information about the studied objects.

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r-m and with k A. M of Reconstruction of densities from their projections with applications in radiological physics, Phys. Med. Biol., v. 18, p. 195, 1973; Gambarelli J. o. Computerized axial tomography, B. — N. Y., 1977; H an a g a J.

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