Optical fiber temperature sensor used in human body temperature monitoring during the working process of nuclear magnetic resonance equipment

Nuclear magnetic resonance imaging (NMRI for short), also known as spin imaging, also known as magnetic resonance imaging (MRI for short), also known as magnetic resonance imaging in Taiwan, and also known as magnetic resonance imaging in Hong Kong, is based on the principle of nuclear magnetic resonance (NMR for short). The released energy attenuates differently in different structural environments inside the substance. By applying a gradient magnetic field to detect the emitted electromagnetic waves, the position and type of the nuclei of the object can be known, and the structure image of the object can be drawn based on this.

Magnetic resonance imaging is a relatively new medical imaging technology that has not been officially used in clinical practice until 1982. It uses static magnetic field and radio frequency magnetic field to image human tissues. In the imaging process, neither electron ionizing radiation nor contrast agent is used to obtain a clear image with high contrast. It can reflect the abnormalities and early pathological changes of human organs from the inside of human molecules. It is superior to X-ray CT in many places. Although X-CT solves the problem of human body image overlap, because the image provided is still the spatial distribution image of tissue absorption of X-rays, it cannot provide information on the physiological state of human organs. When the absorption coefficient of the diseased tissue is the same as that of the surrounding normal tissue, it cannot provide valuable information. Only when the disease develops to change the organ shape, position and enlargement of itself, it can be found. In addition to the anatomical characteristics of X-ray CT, the magnetic resonance imaging device can obtain non-overlapping proton density tomographic images. It can also use the principle of nuclear magnetic resonance to accurately measure the nucleus relaxation time T1 and T2, which can correlate the relationship in human tissues. The information of the chemical structure is reflected. The image reconstructed from this information by the computer is a composition image (chemical structure image), which has the ability to display different chemical structures of the same density and the same tissue through the image display. This makes it easy to distinguish gray matter and white matter in the brain, and has great advantages in early diagnosis of tissue necrosis, malignant diseases and degenerative diseases, and the contrast of soft tissue is more accurate.
The nuclear spin has angular momentum. Because the nuclei are charged, their spin generates a magnetic moment. When the nucleus is placed in a static magnetic field, the originally randomly oriented bipolar magnet is subjected to the force of the magnetic field and oriented in the same direction as the magnetic field. Taking proton, the main isotope of hydrogen, for example, it can only have two basic states: orientation "parallel" and "antiparallel", which correspond to low-energy and high-energy states, respectively. Accurate analysis proves that the spin is not completely aligned with the magnetic field, but is tilted by an angle θ. In this way, the bipolar magnet begins to precess around the magnetic field. The frequency of precession depends on the strength of the magnetic field. It is also related to the type of nucleus. The relationship between them satisfies the Larmor relationship: ω0=γB0, that is, the precession angular frequency ω0 is the product of the magnetic field strength B0 and the magnetic spin ratio γ. γ is a basic physical constant of each nuclide. The main isotope of hydrogen, proton, is abundant in the human body, and its magnetic moment is easy to detect, so it is most suitable for obtaining MRI images from it.
In pure metallic copper, the spontaneous order temperature of nuclear magnetic moment is about 10-7K. When T>10-4K, the change of nuclear magnetization M with temperature obeys Curie's law x=\frac{C}{T}=\frac{bb{M}}{bb{H}_0}, where H0 is an external magnetic field. After M, the temperature T can be determined. From the display in the figure, suppose the external field H0 is in the z-axis direction and the magnetization M is in the same direction. If a pulsed magnetic field Hy is applied in the y-axis direction, the combined magnetic field is Hr=H0 Hy, At this time, M precesses around Hr. Assuming that M precesses to an angle θ with the z-axis, the pulse field exits, then M will precession around H0, and its projection Msinθ on the xy plane will be placed in the x-axis direction A sinusoidal voltage is induced in the receiving coil of, due to the interaction between nuclear spins, the θ angle will gradually decrease, and the induced voltage will present a form of sine wave with attenuated amplitude. Its initial amplitude KaTeX parse error: Undefined control sequence: \piebb at position 10: V=\frac{4\̲p̲i̲e̲b̲b̲{H}_0^2rA\etaNs... Volts, where A is the cross-sectional area of ​​the receiving coil, N is the number of turns of the receiving coil, and η is the magnetic coupling between the temperature measurement body and the coil The fill factor of r is the gyromagnetic ratio of the nucleus. But the molecular part of the relational formula is all constants, so it can be determined by a temperature fixed point, which is a mK-level thermometer.

Finally, I recommend a fiber-optic sensor for temperature monitoring in nuclear magnetic resonance inspections. The fiber-optic temperature sensor-THR-NS-1084A introduced by Gongcai.com from abroad. Based on product design, this temperature probe can meet the needs of overheating all over the world. The operability and reliability required by scientists and developers who are active in the field of hyperthermia. It has the advantages of temperature resolution, small probe size, excellent repeatability, easy insertion, long-term stability and so on.