APPLICATION OF WIRELESS COILS IN FLUORINE-19 MAGNETIC RESONANCE IMAGING

 

N. V. Anisimov ¹, M. V. Gulyaev ¹, D. V. Volkov ², O. S. Pavlova ^1,2, Y. A. Pirogov ²

¹ Lomonosov Moscow State University, Faculty of Fundamental Medicine

² Lomonosov Moscow State University, Faculty of Physics

 

The paper is received on November 13, 2016

 

Abstract. It is described how to use the wireless coils for NMR signal amplification in magnetic resonance imaging (MRI), including in vivo experiments using small laboratory animals. Interest in such coils is due to the fact that they can be implanted in the body of a living object. In this case, they can be located very close to the investigated organ. If this coil is tuned exactly on the Larmor frequency and inductively linked with two-way transmitting resonator, then registered NMR signals can have significant increase in sensitivity. The effect is achieved, firstly, by increasing the RF field near the coil surface, and secondly, due to the resonant amplification of induction signal from precessing spins. In both cases, the gain is determined by the product of the mutual induction coefficient on wireless coil quality. As wireless coil, the firm surface coil originally designed for recording signals from protons at a frequency of 300.3 MHz was used. This coil was modified – readjusted for work on Larmor frequency of fluorine-19. Such modification was realized as well for branded resonator which creates exciting RF field near by wireless coil and receives spin system response, reinforced by the same coil. Good results by ¹⁹F NMR spectra registration were obtained even with the resonator, which was tuned to the NMR frequency protons and worked like a non-resonant contour. Using it in conjunction with wireless coil allowed to enhance the NMR signal in 18 times. For obtaining MRI images, the modified resonator in conjunction with wireless coil was applied. When a signal from fluorine-containing drug, placed in ampoules, has being registered, a more than fivefold increase in the signal was achieved. A sufficiently large (more than 2 times) gain was obtained during in vivo experiments with using the gradient echo method to register signals. The modified resonator tuned to the fluorine-19 frequency and the tuned to the same frequency wireless coil was used in these in vivo experiments. Without using the latest one, it would be required significantly more time for obtaining MRI images. Thus, the use of wireless coils allows to increase the NMR sensitivity, simplify problems with RF cables wiring to the examined object, and solve the problem with the lack of MRI sensors for nuclei other than protons.

 Key words: implants, wireless coil, resonator, 19F NMR, 19F MRI, fluorocarbons, spin echo, gradient echo.

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