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An essentially new important step towards provision of national medicine with its own high-tech instruments was taken at the Lebedev Physics Institute (FIAN). According to the Scientific Information Agency FIAN-Inform, the institute developed test samples of all components of a unique full-scale magnetic resonance tomograph (MRT) with a helium-free cooling system. In its characteristics the tomograph will compete with similar instruments of foreign companies leading in the world market of medical technology.

Let's point out here that MRT is the most precise, sensitive and safe method of human organism diagnostics based on the phenomenon of nuclear magnetic resonance (NMR) discovered in 1946 by Felix Bloch and

Orthopaedic tomograph MRScaneks developed by FIAN specialists.

стр. 65

Richard Purcell (USA), Nobel Prize winners. Early in the 1970s the American chemist Paul Lauterbur received the world's first NMR image of two glass capillaries filled with liquid. Besides, his British colleague Peter Mansfield developed a mathematical apparatus for a processing of radio signals received from the instrument with their consequent interpretation into a two-dimensional image. It took another eight years to introduce NMR into medical practice, and the first tomographs appeared in clinics only in 1980-1981.

In the last decade the magnetic resonance tomography actually overshadowed all other diagnostic methods. Even today due to this method it is possible to diagnose malignant tumours, inflammations, cysts, cerebral thromboses, multiple sclerosis, Alzheimer's disease, dislocations, fractures and displacement of intervertebral disks. The prospects for this method in future are limited only by the scope of our imagination.

Until recently MRT complexes were produced only abroad. Three years ago a team of the FIAN scientists headed by Yevgeny Demikhov, Dr. Sc. (Phys. & Math.), decided to fill the gap on our medical market and developed the first national orthopaedic tomograph with a helium cooling system for visualization and diagnostics of the state of limbs and joints. Its design is based on a superconducting solenoid which provides for magnetic induction of 1.5 tesla in the working zone. Diagnostic studies under such parameters take only several minutes. Moreover, one managed to achieve an unusual "sharpness of vision" of the device-up to 0.6 mm, which made it possible to differentiate the minutest particulars of the human organism, earlier inaccessible for visualization.

The decrease in liquid helium use for superconducting magnet cooling is one of the global scientific problems of MRT. Helium is expensive (2,000 liters needed for filling one tomograph costs ~1.5 mln rubles). Besides, the management of a clinic has to invite specialists from outside for an initial filling of the tomograph with liquid and its further periodic replenishment. The Russian scientists solved this problem by opposing coolants of a special type to liquid helium with other coolants, the so-called cryo-refrigerators. As a matter of fact it is a modification of refrigerators in which traditional freon is substituted by gaseous helium. While a regular device maintaining low temperature can freeze the contents to - 80 °C, cryore-frigerators cool "the filling" to T = 4 K (about -269 °C), i.e. to a critical temperature for transition to the superconducting state.

The FIAN specialists made provision for a closed cycle cooling system implying utilization of minimum volume of helium in an orthopaedic tomograph. Superconducting solenoid was placed in a cryostat specially developed for such purpose and filled with liquid helium once a year. While the latter evaporated, it condensed on a heat exchanger which was cooled by a low-temperature cryo-refrigerator. Yevgeny Demikhov stated that if there were no leakages through different seal assemblies, there would have been no need in adding helium at all. Such operating principle of the tomograph allows saving up to 400 liters of expensive helium per year. By the way, this is what the Physics Institute consumes on average for a year.

The technologies tested on compact diagnostic systems formed a basis for a full-scale tomograph, which allowed to study man full length. The FIAN specialists have already developed a tomograph model and separate components in the form of experimental samples, including a gradient-correcting module, a complex of control electronic system and radio frequency coils. This innovative system is also called a "dry" tomograph as use of liquid helium is not stipulated there.

The MRT parameters will be handy for physicians. The magnetic field strength is 1.5 tesla, and the diameter of a tunnel for placing a patient is 60 cm (several times more than in the previous model). Demikhov noted: "The new tomograph differs radically in scale from the previous one. The coil mass together with the cryostat makes up ~3 t, and its diameter is ~2 m. It turns out that the sizes increased 3-4 times. This complicates the problem as a whole and first of all calculations of the magnetic field. Therefore, the main thing now is to provide structural strength, software system operation and an optimal distribution of the magnetic field in the tomograph."

According to FIAN specialists, despite the large sizes the new device will be simpler and more reliable than the existing ones. By approximate calculations its cost will be several times less than that the foreign analogs. Implementation of the ambitious project will enable Russia to join the countries-producers of MRT systems.

O. Ovchinnikova, "On the Way to Helium-Free Tomograph", Scientific Information Agency FIAN-Inform, July 30, 2014


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HELIUM-FREE COOLING OF A TOMOGRAPH // Chisinau: Library of Moldova (LIBRARY.MD). Updated: 24.11.2021. URL: https://library.md/m/articles/view/HELIUM-FREE-COOLING-OF-A-TOMOGRAPH (date of access: 18.04.2024).

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