| With the increasing incidence of diabetes year by year,there is an urgent demand for noninvasive monitoring of blood glucose.The development of middle and low field nuclear magnetic resonance(NMR)technology provides a new possibility for the non-invasive detection of blood glucose.The key technologies involved in the portable NMR instrument for the non-invasive detection of human finger blood glucose were studied in the thesis.Some new methods and technical improvements were proposed.The important achievements of the thesis are as follows:(1)A novel radio frequency(RF)coil-T coil with high RF field homogeneity used for the signal detection of finger blood glucose was designed and developed.First,the Loop-gap coil structure was determined as the basic structure.An improved model T coil based on the Loopgap coil was proposed through theoretical calculation and numerical analysis.The agglomeration effect of current density at the coil end was strengthened.The optimal parameters of the coil were optimized by the finite element analysis method.Then,the production of the RF probe based on the T coil was completed.The experimental results verify that the T coil has the optimal RF field homogeneity and has the smallest distortion of the measured human finger relaxation signal.The special mechanism of the relaxation signal in an inhomogeneous RF field was analyzed theoretically and the reason for the distortion was explained.(2)A novel Halbach magnet with low length-to-inter diameter ratio and excellent magnetic field homogeneity for the signal detection of finger blood glucose was designed and developed.First,the basic theory of the Halbach magnet with a low length-to-inner diameter ratio and the factors affecting the magnetic field homogeneity were studied.A multi-layer magnetic ring structure for magnetic field homogeneity compensation was proposed.The optimal size was determined by the parameter and algorithm optimization of the compensation structure.Then,based on the simulation method of magnetic field inhomogeneous terms,a novel passive shimming method was proposed by analyzing the spatial distribution of small magnetic blocks and the characteristics of the magnetic field harmonic inhomogeneous terms.This method avoided the demagnetization of the magnetic blocks which were placed reverse in the near remaining magnetic strength environment(The magnetic field in the thesis is 1.08 T).Magnetic block diversity combinations compensate for the problems brought by spatial constraints.The actual shimming work proved that the proposed shimming method had a high shimming efficiency.Finally,the development of the new Halbach magnet was completed by designing the magnet assembly process and analyzing the workflow of the new passive shimming method.The magnetic field in (?)20 mm × 10 mm region was 47.7 ppm and the magnetic field in (?)5 mm× 1 mm region was 1.98 ppm.(3)A portable NMR instrument for the signal detection of finger blood glucose was developed.First,a high-precision magnet temperature control system was designed.A resonant frequency drift of only 6.6 ppm within 2 hours was achieved.Combined with the developed magnet and probe,an MRI instrument with the gradient coil(homemade),preamplifier(homemade),duplexer(homemade),spectrometer and power amplifier was completed,which was suitable for the signal detection of finger blood glucose.Then,the instrument performance was experimentally tested.The magnetic field 5 Gs line of the instrument is on the sphere with the origin as the instrument center and a radius of 40 cm.It meets the environmental safety requirements of the magnetic field strength.Magnetic resonance imaging(MRI)of the okra was performed,and the obtained images were clear with a resolution of 156 μm and 156 μm.Finally,the good test stability of the finger signal was proved,and the correlation between the relaxation signal of human fingers and the blood glucose value was explored. |
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