A Multinuclear Low Field Magnetic Resonance Minitomograph
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ICAL INSTRUMENTS FOR ECOLOGY, MEDICINE, AND BIOLOGY
A Multinuclear Low Field Magnetic Resonance Minitomograph V. V. Frolova, K. V. Tyutyukina,*, S. A. Shubinb, S. A. Lavrova, and Yu. V. Bogachevc a St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia b Intelligent IT Systems LLC, St. Petersburg, 199034 Russia cSt. Petersburg State Electrotechnical University (LETI) ul. Professor Popov, 5, St. Petersburg, 197022 Russia * e-mail: [email protected]
Received March 18, 2020; revised April 5, 2020; accepted April 10, 2020
Abstract—A laboratory magnetic resonance imager for small objects that operates in a field of 7 mT is described. The hardware of the tomograph makes it possible to perform experiments on different nuclei and to use double irradiation methods. The high degree of absolute uniformity of the constant magnetic field allows the use of relatively weak gradients to obtain images. The tomograph can be used to develop new methods of magnetic resonance imaging for the purpose of training physicists and engineers in the methods of obtaining magnetic resonance images and for the study of small objects. DOI: 10.1134/S0020441220050127
INTRODUCTION In the last decade, there has been a renewed interest in research in the field of nuclear magnetic resonance (NMR), including magnetic resonance imaging (MRI), in very weak magnetic fields compared to those used in common devices (millitesla units and below) [1, 2]. Interest in such studies is caused, on the one hand, by the extremely high cost of equipment that operates in strong magnetic fields and uses liquid helium or magnetic materials based on rare-earth elements. On the other hand, as the authors of [3] noted, 80% of all diagnostic examinations can be performed in much weaker fields. It should be noted that in addition to high cost, there are other negative factors caused by the use of a very strong magnetic field and, therefore, high radio frequencies (up to hundreds of megahertz). Since a living organism is a conducting medium, with increasing frequency the risk of overheating of tissues and exceeding the specific absorption rate (SAR) increases [4]. In addition, the conducting medium becomes an additional source of noise [5], which weakens the effect of improving the signal-to-noise ratio with increasing field level. One of the negative factors is also a decrease in relaxation contrast due to the phenomenon of frequency dispersion of relaxation times [2, 6]. In addition, a strong magnetic field and high frequency create difficulties in examining some groups of patients [4]. It is impossible to examine patients with metal implants and pacemakers and there are difficulties with people who suffer from claustrophobia, while
some people do not tolerate the noise made by the gradient system. This work describes a low-frequency magnetic resonance imager developed at the Department of Nuclear Physical Research Methods at St. Petersburg State University for small objects with the possibility of irradiation at the resonance frequencies of
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