NUCLEAR MAGNETIC RESONANCE

From Big Medical Encyclopedia

The NUCLEAR MAGNETIC RESONANCE (NMR) — the selective absorption substance of electromagnetic radiation caused by reorientation of magnetic moments of the atomic kernels which are in constant magnetic field. The method of studying of structure and molecular movement in various substances, including in biol is based on the phenomenon of nuclear magnetic resonance. objects. By means of nuclear magnetic resonance, in particular, studying of a structure of various bodies, distributions of various substances directly in an organism is possible.

The phenomenon of nuclear magnetic resonance is based that atomic nuclei of the majority of chemical elements (except for kernels with an even number of protons and neutrons) possess so-called spin, i.e. the moment of number of the movement and the constant magnetic moment caused by it (see Atom, the Molecule). During the room in constant magnetic field magnetic moment of system of kernels it is similar to the rotating top brought out of vertical position, H0 where at — a constant for each type of kernels, and H0 — tension of constant magnetic field moves on a surface of a cone of rotation around an axis of the direction of the field (the precession movement) with a frequency with = at •. Influence of external variable electromagnetic radiation with this frequency on the kernels which are in constant magnetic field leads to selective (resonant) absorption of energy of electromagnetic radiation and emergence of a signal of nuclear magnetic resonance (see. Electromagnetic radiation, Resonant phenomena). To different kernels there correspond various frequencies of a resonance which are ranging from units to hundreds of megahertz in magnetic fields tension about 1 — 10 T. This area of frequencies belongs to the radio-frequency range of electromagnetic waves therefore nuclear magnetic resonance is one of methods of radiospectroscopy (see Radiations, the Electronic paramagnetic resonance). For studying biol. systems usually use nuclear magnetic resonance of kernels of hydrogen —

protons of HN (a proton magnetic 2nd

resonance) and a deuterium of HN, carbon

? With, sodium, phosphorus and other kernels.

Use of nuclear magnetic resonance for structural researches is based that in addition to external magnetic zero the kernel in substance is affected by various internal fields. They lead to a frequency shift of a resonance, splitting to several or set of resonant lines, i.e. to formation of a range of nuclear magnetic resonance, to change of a form of lines, time of a relaxation (see. Relaxation phenomena). Studying of ranges of nuclear magnetic resonance allows to draw a conclusion on chemical and spatial structure of various substances without carrying out the chemical analysis.

The equipment for registration of ranges of nuclear magnetic resonance includes the magnet creating the field tension to 10 T and more, the generator of radio-frequency fluctuations, the receiver in the coil to-rogo the studied object, and the chart recorder is located. Record of ranges is carried out or at change of size of magnetic field and consecutive creation of resonant conditions for different lines in a range of nuclear magnetic resonance, or by excitement of a resonance in all spectral band by means of a powerful radio-frequency impulse at once that sharply reduces time of measurements. An initial range of nuclear magnetic resonance then receive according to the special program by means of the COMPUTER.

In medicobiological researches the nuclear magnetic resonance method is used for establishment of structure of biologically active agents and studying of mechanisms of their action. Determine features of structure of biopolymers in an aqueous medium by ranges of nuclear magnetic resonance and its changes at interaction with substrate and biologically important substances. Ranges of nuclear magnetic resonance apply to the analysis of lipidic structure of membranes, their phase state, interaction of lipids with proteins and other substances, to definition of situation in membranes of various connections, permeability of membranes, a condition of ions in cells, to definition of products of biochemical reactions etc. By means of the nuclear magnetic resonance method became possible to measure amount of ATP and other makroer-tichesky connections and their change directly in an organism (fig. and, b). Important feature of the nuclear magnetic resonance method, especially for biology and medicine, low energy of pspolzuyemy radiations in nuclear magnetic resonance is that significantly reduces their harmful effects on an organism.

A picture of spacing of separate types a pier -


Fig. Ranges of nuclear magnetic resonance of the newborn with a tumor of the left cerebral hemisphere (on phosphorus 31P): on abscissa axis million shares (m of) from the size of the enclosed constant magnetic field, on ordinate axis — values of amplitude of a signal in conventional units are postponed (conventional unit.). Separate peaks correspond to levels of concentration of phosphoric groups of molecules of adenosine triphosphoric acid (ATP) and creatine phosphate (KF). In the left hemisphere (b) unlike right concentration of ATP and KF is sharply reduced.

cool in an organism receive by method of a nuclear magnetic resonance nondestructive testing (YaMR-tomogra-fii). Creation by means of consistently enclosed gradients of magnetic field in various directions of such distribution of magnetic field that at present to various elements of volume within the studied section there corresponded the, determined for their location frequencies of a resonance is its cornerstone. Change of gradients in time and processing of results of measurements with the COMPUTER allow to receive a space picture of distribution of the molecules containing, e.g., hydrogen atoms or phosphorus (at observation of magnetic resonance from protons or kernels of phosphorus) within the studied section.

At registration YaMR-izobrazhe-niya amplitude of a resonance in each element of volume can be expressed through intensity of lighting or in a color scale. So, blood vessels in the nuclear magnetic resonance image look dark owing to outflow of blood from the studied volume during measurement. For magnetic moments of kernels time of a relaxation, in particular on reduction of amplitude of a resonance which is not in time to be recovered completely with rather big frequency of following of impulses can be measured in various elements of volume. It increases contrast in the image of various fabrics that is used, e.g., for distinguishing of the image of gray matter of a brain from white or tumor cells from healthy. The advantage of a method of a nuclear magnetic resonance nondestructive testing is its high sensitivity in the image of soft tissues (see tsvetn. the tab., Art. 400, fig. 16 — 19), and also

high resolving power, up to shares of millimeter. Unlike a x-ray tomography (see) The nuclear magnetic resonance nondestructive testing allows to receive images of the studied object in any section. On this basis volume images of separate bodies can be reconstructed. Obtaining the image by means of a nuclear magnetic resonance nondestructive testing can be synchronized with certain cycles fiziol. processes (e.g., with cycles of cardiac performance, teeth of an ECG etc.). Bibliogratsarkin A. V., etc. A nuclear magnetic resonance nondestructive testing, At the joint venture. fizich. sciences of t. 135, century 2, page 285, 1981, bibliogr.;

Günter X. Introduction to a course of spectroscopy of nuclear magnetic resonance, the lane with English, M., 1984, bibliogr.; C y A. F., etc. Medical nuclear magnetic resonance — spektro-and a nondestructive testing, achievements and perspectives, Medical radio-gramophones of t. 28, No. 6, page 86, 1983; Emsli D.,’ Finey D. and Sutcliffe JI. Spectroscopy of nuclear magnetic resonance of high-res, the lane with English, t.

1 — 2, M., 1968 — 1969; Casy A. F. PMR spectroscopy in medicinal and biological chemistry, L. — N. Y., 1971; G a d i-a n D. G. Whole organ metabolism studied by NMR, Ann. Rev. Biophys. Bioeng. v. 12, p. 69, 1983, bibliogr.; Klaus R.’ NMR-Tomographie und-Spektroskopie in der Medizin, B. u. a., 1984;

Mans field P. Morris P. G. NMR imaging in biomedicine, N. Y. — L., 1982 * NMR in biology, ed. by R. A. Dwek a. o’ L. a. o., 1977.

S. I. Aksenov; V. I. Krutsky (author tsvetn. slides).

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