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