The Magnet Design And Experiment Research Of Semi-ring Single-sided NMR Sensor

Single-sided NMR has been widely used in medical field as a nondestructivemethod. Although the nuclear magnetic resonance imaging (MRI) technology andother imaging diagnosis and treatment which based on other imaging methods aredeveloping rapidly, and largely reduce the patient’s pain, they still can not meet thedemand of the reality of clinical.Skin burn is a common disease, and the current method for judging the depth ofburn is relatively rough and subjective. At present, the degree of skin heat and burntime is the main judgment method, at the same time, skin symptoms and with orwithout pains being as a second judgment.This subjective judgment may cause the internal organization worse rapidly, burndegree being further strengthened. Now, to judge the burn and recovery degree, andmake treatment and rehabilitation plan, a new quantitative and accurate method isrequired in clinical.Considering no appropriate method in clinical to judge the degree of skin burnand its recovery after diagnosis, which mainly judged by doctor’s subjective judgmentand patients feel at present, the main purpose of this paper lies in designing a small andhandheld single-sided magnet in order to monitor the skin burn real-time. The magnetand figure8RF coil form the NMR sensor which is used to do the corresponding NMRexperiments. Specific content includes the following several aspects:①Calculation of permanent magnet magnetic field and design single-sidedmagnet. The source of the magnetic field is seen as magnetic charge, scalar magneticpotential φmis the solving variable. To derive the magnetic potential at any point in thespace, ten nodes tetrahedron element is introduced to discrete the whole area, withinthe quadratic model of scalar field φmbeing established in the element. Based onsecond-order finite element method, a single-sided magnet with semi-ellipticalstructure which consists of seven magnets is equivalent to elliptical mathematicalmodel. The size of the final magnet is4.5cm×10.5cm×10.5cm, and weights about1.5kg. It is a handheld magnet. The magnetic field in the horizontal plane is flat andhas a constant gradient in the vertical direction. The B0field decreases from96mT to57mT by a constant gradient of3.9T/m in the vertical direction in ROI. Compared withthe simulation field values, the measured field values which measured by a gauss meter have an error about1%.②Calculation of radio frequency field. Based on Biot-Savart law, the magneticfield which produced by a long straight wire is acquired at any position in the space.The RF magnetic field of the RF coil which has4.5turns is calculated and its RF fieldsdistribution are shown in the paper. As the results shown, RF field is flat in a big areain the horizontal plane, and has a gradient in the vertical direction, but it is not constant.In order to get the maximum transmission power, RF coil is connected to a tuning andmatching circuit.③NMR experiments. Three experiments are done by NMR experiment platform：1）Performance test of NMR sensor. Measuring the echo signal of rubber, and it is clear;The sensor can get clear relaxation time decay curve, and the measured T2effof purewater is131.4ms, rubber of12.3ms; The result of testing RF coil of received signalexperiment shows that the RF coil can work throughout the area in the plane, but themaximum measured depth of RF coil is within3mm, and in this range,one-dimensional profiling figure is clear.2）Measuring the liquid diffusion coefficientD. The value of D is close to the test environment temperature. Take pure water as anexample, the result is D=2.2×10-9m2/s.3）Aging detection method for silicone rubbercomposite insulator based on NMR principle. Three kinds of silicone rubber compositeinsulators with different running years are tested, and the results show that the top andbottom surface of the same silicone rubber composite insulator have differentequivalent transverse relaxation time T2eff; T2effdecreases as the service time of theinsulator increases; T2effdecreases as the measurement moves from the middle part tothe surface of the shed; Compared with the change trend of static contact angle, theyhave the same change trend, but the change trend of T2effis more obvious.A variety of NMR experiments in this paper show that the design method and themagnet structure based on second-order finite element method are available.