| Traumatic brain injury, intracranial space-occupying lesions, intracranial inflammation, cerebrovascular disease and cerebral anoxia, all of these can cause encephaledema directly or indirectly. The development of this kind of disease is unexpected and fast course. It’s inappropriate to move the patients and they can’t get real-time detection. Patients can’t be treated in time, so this kind of disease leads to a high mortality.At present, nuclear magnetic resonance(NMR) instruments have complex structures, large volume, inconvenient to be moved, and the diagnosis is expensive. It is difficult to achieve real-time monitoring of clinical. Besides, they are large enclosed equipment, it’s inapplicable to the patients with claustrophobia and cardiac pacemaker or have some metal objects in body, etc. At the same time, considering the specific conditions of our country, primary health care is promoting currently. Configuring noninvasive real-time monitoring equipment which is small and cheap in basic medical units has a great effect on relieving the tension of large medical resources. Therefore, a small, portable, cheap equipment that can provide real-time monitoring by the bed in clinical is needed urgently. It can provide patients’ condition change for doctors in time, so doctors can determine and change the treatment plan to save the lives of patients.In this paper, open nuclear magnetic resonance(ONMR) measurements and imaging about encephaledema detection were studied, a set of ONMR system to detect brain edema was designed. It’s small and can be moved easily, at the same time, it has a low price. It meets the demand of clinical needs and provides real-time monitoring for patients with brain diseases.The main work are as follows:(1) NMR theory research and the main magnet field research. NMR imaging principle was studied deeply, the system was designed on the basis of the principle. The strength of the NMR signal is related to the density of hydrogen nuclei, and the density of hydrogen nuclei is related to water content; water content change can cause tissue morphological change(the proportion of free water and bound water is changed), so transverse relaxation time T2 is different.The encephaledema can be reflected by the signal strength and T2. On this basis, the system was designed and the experiment was conducted. The magnetic field of main magnet was measured in needed area, the data was analyzed and processed for the RF coils’ design and experiment.(2) Design of RF coils. According to the main field, a variety of RF coils were designed(cage coil, single-layer splayed coil, double-layer splayed coil, circular spiral coil), magnetic field of the coils were studied. Coils were modeled and simulated in Maxwell, and the magnetic field of the coils were analyzed qualitatively. Double-layer splayed coil and circular spiral coil were selected according to the uniformity of the magnetic field, parallelism and strength. The calculation method of circular spiral coil magnetic was established through algorithm programming, different factors(coil turns, turn spacing, distance between the two coils, outer radius) on the influence of the magnetic field were studied. Double-layer splayed coil was optimized on the basis of circular spiral coil research, the printed circuit boards(PCB) were produced of coils under different sizes, then further optimized in the experiment.(3) Design of the NMR system. The system design principle of each part was introduced, including the matching circuit, frequency regulation and parameter setting methods, design scheme of the whole system was given. Calculation and processing method of all kinds of data(the average magnetic field B/m T, resonance frequency f/MHz, resistance R/Ω, inductance L/μH, matching capacitor Cm/p F, CT/p F) at different heights were presented. Then calculated Cm, CT and the circuit board was welded, frequency was matched twice. Changing the calculation parameters to change the structure of the coil, until a good NMR signal was obtained.(4) NMR experiment. NMR system was established with double-layer splayed coil. First, experiments with flour and pork as testing samples, T2 was measured under different water content by changing injected water volume of each sample. Different T2 reflected the change of water content, T2 was proportional to water content. Second, with cosmetic cotton as testing sample, one-dimensional layered experiment was carried out. NMR signal strength changed with water content change, which is representated through the area surrounded by echo signal and horizontal axis. Two-dimensional figure of signal was drawn out at the same time, the water content can be read easily. Third, with paste as testing sample, the NMR signals at different angular positions were measured, this measurement method can well solve the problem of measuring depth of the RF coil. Measuring depth is limited for double-layer splayed coil, it is only 3 mm in the experiment. But the signal strength was stronger and the accuracy up to 0.01 m L. Fourth, considering the limitation of double-layer splayed coil measuring depth, NMR system was established with double-layer splayed coil, problem of the coil measuring depth was solved. The measuring depth is up to 10 mm. These experiments verified the practicality and feasibility of the system in this paper. |
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