N.V. Anisimov – Dr.Sc.(Phys.-Math.), Senior Research Scientist, 
Faculty of Fundamental Medicine, Lomonosov Moscow State University
E-mail: anisimovnv@mail.ru
A.A. Tarasova – Student, 
Department of Phisics, Lomonosov Moscow State University
E-mail: arina.tarasova99@mail.ru
Yu.A. Pirogov – Dr.Sc.(Phys.-Math.), Professor, 
Department of Phisics, Lomonosov Moscow State University E-mail: yupi937@gmail.com

In the article, the question of the possibility of registering sodium (23Na) signals at low field MR scanner for medical diagnostic applications was studied. The experiments were carried out on a clinical 0.5T scanner, which only included additional coils tuned to the 23
Na NMR frequency. Proprietary receive-only coils for registration of proton signals (21.1 MHz) were taken as a basis. They were modified to record sodium signals (5.6 MHz). To do this, they were retuned in frequency by changing their inductances and capacitances. Inductances of coils were changed by removing inter-turn capacitances. In addition, coils belonging to different quadrature channels were connected in series, due to it the quadrature (two-channel) coils were transformed into single-channel ones. In addition, receive-only coils were transformed into transceivers. To do this, low-voltage and low-current elements, such as varicaps, etc., intended for electronic tuning of the receiving circuit, were removed from the electronic nodes of the coils. They were replaced by multi-turn high-voltage capacitors. For testing coils, scanning of human organs was carried out on the example of three healthy volunteers. It was noted that the scanning efficiency can be improved if the parameters of the elements of the transmitting channel (high-power amplifier, transmit/receive switch) are optimized on the NMR frequency of sodium, though in the proprietary version they were optimized on the NMR frequency of protons. The parameters of the receiving path can be improved (SNR increased by 1.4 times) when restoring quadrature schemes of signal registration. It is concluded that the use of large-size coils for low-field 23Na MRI is inefficient. In our case, volume saddle-type coils belong to these. More promising is an use of coils, turns of which can be placed close to the zone of interest, as well as coils of small size and adapted to organs, the placement of which in the coil ensures its high filling factor. In our case, this applies to solenoidal, surface and frame coils. An assumption is made about the productivity of using 23
Na NMR spectroscopy to evaluate the sodium content in various organs.

Anisimov N.V., Tarasova A.A., Pirogov Yu.A. Transceiver coils for recording sodium signals on a 0.5 T magnetic resonance scanner. Electromagnetic waves and electronic systems. 2020. V. 25. № 4. P. 28−36. DOI: 10.18127/j15604128-202004-04. (in Russian)

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