| The traditional nuclear magnetic resonance(NMR)detection needs a huge magnet to surround the whole human body,which increases the production and maintenance cost of the instrument and limits the application and promotion of NMR technology in medicine.Unilateral magnetic resonance uses small volume magnets to detect large samples of magnetic resonance signals,which promotes the development of portable magnetic resonance technology.Based on the theory of unilateral permanent magnet design,special unilateral permanent magnets are designed to solve the portable unilateral NMR testing problems for important diseases such as breast cancer,blood sugar and fatty liver.The specific results achieved are as follows.(1)Development of portable unilateral magnet for non-invasive detection of human breast with large target area.From the perspective of non-invasive detection of human breast,a new large target area unilateral magnet based on semi ellipse is proposed.The magnetic field distribution is improved by adding iron yoke and optimizing structural parameters.In the hemispherical target area with a radius of 5.5cm,the minimum value of magnetic field is51.8m T,the gradient is 0.42T/m and the magnet mass is 24.1kg.To reduce the overall mass,a unilateral magnet based on multiple groups of rectangular magnetic rods is obtained by unrolling the Halbach magnet.After structural parameter optimization and truncation compensation,the minimum value of magnetic field in the hemispherical target area with a radius of 5.5cm is 50.4m T,the gradient is 1.35T/m,and the magnet mass is reduced to 10.9kg.(2)Development of high homogeneous unilateral magnet for human blood glucose detection.From the magnetic field distribution of two-dimensional rectangular permanent magnet with uniform saturation magnetization,a magnetic field distribution of single-sided magnet structure composed of multiple rectangular magnetic rods with the same magnetization direction is deduced.The first and second derivatives of the magnetic field in the threedimensional target region are zero.Through finite element simulation,in the cylindrical target area with diameter of 3mm and height of 1mm,the magnetic field intensity is 54.38 m T and the inhomogeneity is 442 ppm.After assembly,the measured magnetic field intensity in the target area is 46.67 m T,and the inhomogeneity is as high as 6255 ppm.To compensate the error,stainless steel screws and nuts are used for passive shimming.After passive shimming,the magnetic field intensity in the target area is 46.7m T and the nonuniformity is 1713 ppm,which is 72.6% lower than that before shimming.To build the small unilateral NMR sensor,the duplexer,RF coil and other components are independently developed,and the small unilateral NMR sensor is assembled.The experimental research shows that the designed magnet can meet the needs of portable magnetic resonance detection of blood glucose.(3)Development of portable unilateral magnet for equipotential distribution of magnetic field in human liver.From the perspective of noninvasive detection of human liver fat,a new unilateral magnet with high detection depth is proposed.A pair of magnetic rods are added on both sides of the bottom of the magnet to accurately control the distribution of magnetic field equipotential surface on the magnet surface.The measured magnetic field intensity in the target area is 70 m T,the gradient is 0.9T/m,and the magnetic field equipotential surface is focused in the target area and open on the magnet surface.The results show that the unilateral NMR sensor has a good ability to distinguish liver molds with different oil content under the interference of simulated subcutaneous fat,and can quantitatively detect the oil content of molds.Finally,through the noninvasive detection of volunteers,the application potential of the designed unilateral permanent magnet in portable noninvasive NMR detection of human liver fat is proved. |
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