Nuclear magnetic resonance is a nuclear nucleus with a non-zero magnetic moment. The spin energy level undergoes Zeeman splitting under the action of an external magnetic field, and the resonance absorbs the physical process of radio frequency radiation of a certain frequency. Nuclear magnetic resonance spectroscopy is a branch of spectroscopy whose resonance frequency is in the radio frequency band, and the corresponding transition is the transition of the nuclear spin at the nuclear Zeeman level.
Nuclear magnetic resonance imaging: Magnetic resonance imaging (MRI) has become a common imaging method. As a new imaging technique, MRI does not affect human health, but it is not suitable for nuclear magnetic resonance in six groups. Check: people who have a pacemaker, people with or suspected metal foreign bodies in the eyeball, people with aneurysm silver clip ligation, people with metal foreign bodies remaining in the body or metal prosthesis, critically ill patients at risk, claustrophobia Phobia patients, etc. It is not possible to bring monitoring instruments, rescue equipment, etc. into the MRI laboratory. In addition, pregnant women who are less than 3 months pregnant, it is best not to do MRI.
Nuclear magnetic resonance
Found lesion
MRI is a new medical imaging technology using the principle of nuclear magnetic resonance. It is excellent for brain, thyroid, liver, gallbladder, spleen, kidney, pancreas, adrenal gland, uterus, ovary, prostate and other essential organs as well as heart and large blood vessels. Diagnostic function. Compared with other auxiliary inspection methods, NMR has many advantages such as more imaging parameters, faster scanning speed, higher tissue resolution and clearer image. It can help doctors “see” early lesions that are not easily noticeable. It has become a tumor, heart disease and A tool for early screening of cerebrovascular diseases.
It is understood that because the metal will interfere with the external magnetic field, the patient must remove all the metal objects on the body before performing the MRI. Do not wear magnetic objects such as watches, metal necklaces, dentures, metal buttons, metal rings, etc. for MRI. In addition, with a cardiac pacemaker, there are paramagnetic metal implants in the body, such as metal clips, brackets, plates and screws, etc., can not be magnetic resonance imaging. For the upper abdomen (such as liver, pancreas, kidney, adrenal gland, etc.) magnetic resonance examination must be fasting, but can drink enough water before the examination, which is conducive to clearer boundaries between the stomach and liver and spleen.
Found tumor
Nuclear magnetic resonance is the most effective imaging diagnosis method for diseases such as brain and spinal cord. It can not only detect tumors, cerebral infarction, cerebral hemorrhage, brain abscess, cerebral cysticercosis and congenital cerebral vascular malformation, but also determine the type of hydrocephalus. And reasons, etc. For the first gynecological disease that harms women’s life and health in China, breast cancer, through the accurate screening of nuclear magnetic resonance, can help to find early breast cancer lesions; for the “high blood pressure, high blood fat, high blood sugar” and other three high population, can Through the nuclear magnetic examination of the head and heart, early detection of high-risk diseases such as heart disease and cerebral infarction before the physical health has not yet issued a red light warning. In addition, NMR can also be used for abdominal and pelvic examinations, such as liver, gallbladder, pancreas, uterus, etc., abdominal aorta and extremity vascular imaging can clearly diagnose true, pseudoaneurysm, dissection aneurysm and limb blood vessels Various lesions. NMR is very sensitive to the diagnosis of various types of joint tissue lesions, and is very sensitive to aseptic necrosis of bone marrow and bone.
Harmless to people
Since nuclear magnetic resonance is a magnetic field imaging and has no radioactivity, it is harmless to the human body and is very safe. It is understood that there is currently no report on the use of MRI in the world, and no increase in the incidence of genetic mutations or chromosomal aberrations caused by MRI. Although MRI is unique in screening early lesions, any examination is limited. For example, some patients are not suitable for MRI, so do not over-examine. He appealed that any patient should be examined according to the doctor’s advice. Do not think that the more expensive the image examination, the better. Only the examination that suits you is the best.
Continuous wave nuclear magnetic resonance spectrometer CW-NMR
The nuclear magnetic resonance instruments used today have two forms of continuous wave (CW) and pulsed Fourier (PFT) transformation. The continuous wave nuclear magnetic resonator is mainly composed of a magnet, a radio frequency transmitter, a detector, an amplifier, and a recorder (see the following figure). Magnets are used to generate magnetic fields. There are three main types: permanent magnets, electromagnets [magnetic induction strength up to 24000 Gs (2.4 T)], and superconducting magnets [magnetic induction strength up to 190000 Gs (19 T)].
The resolution of a nuclear magnetic resonance spectrometer is often expressed in terms of frequency (also called “mega”), which is defined as the frequency of the electromagnetic wave required to excite hydrogen atoms under the instrument’s magnetic field. For example, in a superconducting nuclear magnetic field with a magnetic field strength of 9.4T, the excitation frequency of hydrogen atoms is 400MHz, then the instrument is a “400 mega” instrument. High frequency instruments with good resolution, high sensitivity, and simple and easy to analyze maps. The magnet is provided with a scanning coil, which is used to ensure that the magnetic field generated by the magnet is uniform and can be continuously and accurately varied within a narrow range. The RF transmitter is used to generate a fixed frequency electromagnetic radiation detector and amplifier for detecting and amplifying the resonance signal. The recorder plots the resonance signal as a resonance map.
CW-NMR is inexpensive, temperature, easy to handle, but poorly sensitive. Therefore, it is necessary to measure a large number of samples, and only a nuclear with a high degree of natural abundance such as 1H/19F/31P can be measured, and a low-abundance core such as 13C cannot be determined.
PFT-NMR
The pulsed Fourier NMR spectroscopy appeared in the mid-1970s, and its emergence enabled the rapid development of 13C NMR research.
Pulse Fourier transform-NMR (pulse Fourier transform-NMR) is different from continuous wave instrument in that it adds a pulse program controller and data acquisition and processing system, using a strong and short (1~50μs) pulse to treat all the Simultaneous excitation is performed, and the receiving system is turned on in time when the pulse is terminated, and the free induction attenuation signal (FID) is collected. When the nuclear to be excited returns to the equilibrium state through the relaxation process, the next pulse is excited. The obtained FID signal is a time domain function, which is a superposition of signals of several frequencies, which can be recognized by people after being transformed into a frequency domain function by Fourier transform in a computer. PFT-NMR is often sampled multiple times during the test, and then the resulting total FID signal is Fourier transformed to improve sensitivity and signal-to-noise ratio (n-times accumulation, signal-to-noise ratio is improved by n⁰.5 times).
PFT-NMR is highly sensitive and can be used for low abundance nucleuses. The test time is short (one to several seconds) and the relaxation time of the nucleus can be determined.
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