From Big Medical Encyclopedia

X-RAY DENSITOMETRY [rentgeno-(on a name B. X-ray) + densitometry] — the definition of permeability of bodies and fabrics for x-ray emission applied at a research of their structure and function. Distinguish direct R., at a cut directly measure intensity of the x-ray emission which passed through the studied object, and indirect R. (a so-called X-ray photometric method), at a cut measure the optical density of a shadow of the studied object on the roentgenogram or brightness of a luminescence of the respective site of the fluorescent screen.

The river was for the first time carried out in 1927 by P. Stumpf in the form of photometry of teeth on a rentgenokimogramma of heart that was called by it «densografiy». Ya. L. Shik, Yu. N. Sokolov, A. I. Sadofyev dealt with the USSR's first issues P. Now thanks to F. Heuck and Fanzelov's researches (To. Vanselow), Haynttsena (R. of H. Heintzen), W. Rutishauser methods P. reached big accuracy.

The principle P. is used in nek-ry methods of radiodiagnosis — a computer tomography (see. Tomography computer ) and elektrokimografiya (see).

As the independent method P. is applied for differential diagnosis patol. the centers in lungs, overseeing by their evolution under the influence of treatment, definition of ventilating ability of different sites of lungs, studying of movements of heart and large vessels, definition of rate of volume flow of a blood-groove, and also for establishment of content of inorganic matters in bones.

Ventilating ability of various sites of lungs and a condition of focal changes in them throughout a disease are determined by survey roentgenograms by means of a microphotometer of IFO-451 representing a kind of the densitometer (see. Densitometry ). In this device the thin light ray getting through the roentgenogram gets on the photosensor connected with the amplifier and the chart recorder. Uniform advance of a beam allows to analyze the image, fixing sites of various optical density in the form of densitometrical curves. For quantitative assessment of dynamics patol. process use the relations of sizes of optical density, and also the area of the figures formed by densitometrical curves. It is possible to determine degree of clearness of contours by the size of tilt angles of curves patol. educations and vessels. For the correct assessment of dynamics patol. changes in lungs it is necessary to consider possible distinctions of quality of roentgenograms. It is carried out by means of an aluminum plate with in steps decreasing thickness (a so-called step wedge) placed at a X-ray analysis on a film, on to-ruyu make a picture. If the roentgenograms received at different times are identical on quality, then the optical density of a step wedge on each of them will be identical. In the presence of a difference enter a correction factor. Instead of a wedge it is possible to use comparison of optical density of strictly certain sites of anatomical structures (e.g., clavicles, edges).

For the analysis of movements of contours of heart and large vessels, a krovenapolneniye of various sites of lungs use X-ray cinematography (see). The X-ray movie is projected on the transparent opaque screen, on the other hand to-rogo, in the chosen points, the photosensors connected to the amplifier and the chart recorder are strengthened. The same technique is used for determination of speed of a blood flow in vessels. For this purpose by means of the catheter which is carried out through a femoral artery to an aorta or its any branch (renal, coronary arteries) enter 5 — 30 ml of radiopaque substance (e.g., 76% solution of Urotrastum). Change of concentration of radiopaque substance as well as movement of border «radiopaque substance — blood», causes change of intensity of the x-ray emission which passed through a vessel, and respectively change of optical density of certain sites of shots of the X-ray movie. Also determine the speed of a blood-groove by these data. Instead of the movie for the analysis the X-ray television image can be used (see. Videodensitometriya ).

Rubles apply also to determination of amount of mineral substances in a bone tissue by comparison of intensity of a shadow of a bone with a certain thickness of a step aluminum wedge. Relative densitometrical indicators have practical value, to-rye can be used for control of dynamics of maintenance of mineral substances in bones, napr, at an adynamia or local osteoporosis.

Bibliography: Zaretsky V. V. Elektrokimografiya, M., 1963, bibliogr.; The reference book on a radiology and radiology, under the editorship of G. A. Zedgenidze, page 46, M., 1972; Tikhonov K. B. and Fomin Yu. A. Role of densitometry in objectification of the radiological image at patients with various damages of lungs, Vestn. rentgenol. and radio-gramophones., No. 6, page 75,1980; Antonov O. S. u. a. Die densitometrische Beurteilung der Lungen-zeichnung und der Lungendurchblutung im Rontgenogramm bei Patienten mit Herzfeh-lern der Fallotschen Gruppe, Radiol, diagn. (Berl.), Bd 18, S. 55, 1977, Bibliogr.; Den-sitometrie in der Radiologie, hrsg. v. F. Heuck, S. 196, 226, Stuttgart, 1973; Heintzen P. H. A simple method for the recording of radiopaque dilution curves during angiocardiography, Amer. Heart J., v. 69, p. 720, 1965; R u t i s h a u-s e r W. Kreislaufanalyse mittels Ront-gendensitometrie, Bern u. a., 1969; S t and rn p f P., Die objektive, laufende Messung der Schattentiefe von Rontgen-bilden und ihre Bedeutung ftir die Diagno-stik (Densographie), Fortschr. Rontgenstr., Bd 36, S. 695, 1927; W an i b e 1 E. Densi-tometrierung medizinischer Rontgenaufnah-men mit linear Schichtdickenzuordnung, Fortschr. Rontgenstr., Bd 117, S. 207, 1972.

K. B. Tikhonov.