nuclear magnetic resonance, MRI
Nuclear magnetic **** vibration full name is nuclear magnetic **** vibration imaging (MRI), is the magnetic moment is not zero of the atomic nucleus, the role of the external magnetic field under the spin energy level of the Seiman splitting, *** vibration of the absorption of radiofrequency radiation of a certain frequency of the physical process. Nuclear magnetic *** vibration spectroscopy is a branch of spectroscopy, its *** vibration frequency in the radio frequency band, the corresponding leap is the nuclear spin in the nuclear Seeman energy level.
Nuclear magnetic **** vibration is a physical phenomenon that occurs when the nucleus of an atom in a static magnetic field is under the action of another alternating magnetic field. Usually people say nuclear magnetic **** vibration refers to the use of nuclear magnetic **** vibration phenomenon to obtain molecular structure, the internal structure of the human body information technology.
Not all atomic nuclei can produce this phenomenon, atomic nuclei can produce nuclear magnetic **** vibration phenomenon is because of the nuclear spin. Atomic nuclear spin generates a magnetic moment, when the nuclear magnetic moment is in a static external magnetic field produces the incoming nucleus and energy level splitting. Under the action of an alternating magnetic field, the spin nucleus absorbs electromagnetic waves of a specific frequency and leaps from a lower energy level to a higher energy level. This process is nuclear magnetic **** vibration.
Magnetic **** vibration (MRI), also known as magnetic **** vibration imaging technology. It is another major advancement in medical imaging after CT. Since its application in the 80s, it has been developed at an extremely rapid rate. Its basic principle: the human body is placed in a special magnetic field, radio frequency pulse excitation of hydrogen nuclei in the human body, causing hydrogen nuclei *** vibration, and absorption of energy. After stopping the radio frequency pulse, the hydrogen nucleus sends out radio signals at a specific frequency and releases the absorbed energy, which is recorded by the receiver outside the body and processed by the electronic computer to obtain an image, which is called nuclear magnetic **** vibration imaging.
Nuclear magnetic **** vibration is a physical phenomenon, as a means of analysis is widely used in the field of physics, chemistry biology, etc., to 1973 it will be used for medical clinical testing. To avoid confusion with radiographic imaging in nuclear medicine, it is referred to as magnetic *** vibration imaging (MRI).
MRI is a biomagnetic spin imaging technology, it is the use of atomic nuclei spin motion characteristics, in the applied magnetic field, by radio frequency pulse excitation after the generation of signals, detected by a detector and input into the computer, after processing and conversion in the screen to display images.
The amount of information provided by MRI is not only greater than that of many other imaging techniques in medical imaging, but also different from existing imaging techniques, so it has a great potential superiority in the diagnosis of diseases. It can directly make cross-sectional, sagittal, coronal and various oblique images, and will not produce the artifacts of CT detection; does not require injection of contrast medium; no ionizing radiation, no adverse effects on the body.MR is very effective in detecting common cranio-cerebral disorders, such as intracerebral hematomas, extracerebral hematomas, brain tumors, intracranial aneurysms, arterio-venous vascular malformations, cerebral ischemia, intradural tumors, spinal cavernous disease, and hydrocele, etc. It is also effective in detecting lumbar discs, and in detecting lumbar discs.
MRI also has shortcomings. Its spatial resolution is not as good as that of CT, and patients with pacemakers or certain metallic foreign bodies cannot be examined with MRI, which is also expensive.
History of nuclear magnetic **** vibration technology
In the 1930s, physicist Isidor Rabi found that the nuclei of atoms in a magnetic field would be arranged in a forward or backward order parallel to the direction of the magnetic field, and after the application of radio waves, the direction of the atomic nuclei's spin was flipped. This was the earliest human understanding of the interaction of atomic nuclei with magnetic fields and applied radio frequency fields. For this research, Rabi was awarded the Nobel Prize in Physics in 1944.
In 1946, two U.S. scientists Bloch and Purcell found that the nucleus with an odd number of nuclei (including protons and neutrons) placed in a magnetic field, and then applied to a specific frequency of the radio frequency field, the nucleus will be absorbed by the phenomenon of the radio frequency field energy absorption, which is the initial understanding of the phenomenon of nuclear magnetic **** vibration. For this the two of them won the 1952 Nobel Prize in Physics.
People in the discovery of nuclear magnetic **** vibration phenomenon soon after the practical use of chemists to use the molecular structure of hydrogen atoms around the magnetic field generated by the development of nuclear magnetic **** vibration spectroscopy, used to analyze the structure of the molecule, over time, the nuclear magnetic **** vibration spectroscopy technology continues to evolve from the initial development of a one-dimensional hydrogen spectra to the 13C spectroscopy, two-dimensional nuclear magnetic *** vibration spectroscopy, and other high-level spectroscopy. The ability of NM***Vib technology to analyze molecular structure is also getting stronger and stronger, and after entering the 1990s, people even developed the technology to determine the tertiary structure of protein molecules by relying on NM***Vib information, which makes it possible to accurately determine the molecular structure of solution-phase proteins.
In 1946, Purcell of Harvard University and Bloch of Stanford University announced their discovery of NMR, which earned them the 1952 Nobel Prize. Nuclear magnetic **** vibration is the magnetic moment of the nucleus in the constant magnetic field and high-frequency magnetic field (in the radio wave band) at the same time, when certain conditions are met, will produce *** vibration absorption phenomenon. Nuclear magnetic **** vibration soon became a kind of exploration, research material microstructure and nature of high-tech. At present, nuclear magnetic *** vibration has been widely used in physics, chemistry, materials science, life science and medicine and other fields.
The nucleus of an atom consists of protons and neutrons, both of which have an intrinsic magnetic moment. It can be commonly understood that their behavior in a magnetic field is like a small magnetic needle. Atomic nuclei under the action of an applied magnetic field, the nuclear magnetic moment and the magnetic field interaction leads to the splitting of energy levels, the energy level difference is proportional to the strength of the applied magnetic field. If you then add an alternating electromagnetic field corresponding to the energy level spacing at the same time, you can cause the energy level jump of the atomic nucleus, resulting in nuclear magnetic **** vibration. It can be seen that its basic principle is similar to the atom's *** vibration absorption phenomenon.
Early nuclear magnetic **** vibration is mainly used for the study of nuclear structure and properties, such as the measurement of the nuclear magnetic moment, electric quadrupole distance, and nuclear spin, etc., and later widely used in molecular composition and structure analysis, biological tissue and living tissue analysis, pathological analysis, medical diagnosis, non-destructive monitoring of the product and other aspects. For the isolated hydrogen nucleus (that is, proton), when the magnetic field is 1.4T, *** vibration frequency of 59.6MHz, the corresponding electromagnetic wave for the wavelength of 5 meters of radio waves. However, in compound molecules, this *** vibration frequency is also related to the chemical environment in which the hydrogen nucleus is located, in different chemical environments in the hydrogen nucleus has a different *** vibration frequency, called the chemical shift. This is caused by the shielding effect of the electron cloud outside the nucleus against the magnetic field, the induced effect, the ****ear effect and so on. Also spin-coupling splitting occurs due to the interactions of the atoms between the molecules. Using the number of chemical shifts and splits, it is possible to speculate on the molecular structure of compounds, especially organics. This is the spectral analysis of nuclear magnetic **** vibration.In the 1970s, the pulsed Fourier transform nuclear magnetic **** vibrometer appeared, which makes the application of C13 spectrum is also increasing. Material composition and structure analysis by NM***vibration has the advantages of high accuracy, less restriction on the sample, and no damage to the sample.
The earliest nuclear magnetic **** vibration imaging experiments were published by Lauterbur in 1973, and immediately attracted widespread attention, just 10 years into the clinical application stage. Acting on the sample has a stable magnetic field and an alternating electromagnetic field, after removing the electromagnetic field, in the excited state of the nucleus can jump to a low energy level, radiating electromagnetic waves, at the same time can be induced in the coil of the voltage signal, known as nuclear magnetic **** vibration signal. Human tissue due to the presence of large amounts of water and hydrocarbons and contains a large number of hydrogen nuclei, generally with hydrogen nuclei to get the signal than other nuclei more than 1000 times larger. Normal tissue and lesion tissue voltage signal is different, combined with CT technology, that is, electronic computed tomography, you can get any cross-section of human tissue images, especially for soft tissue lesion diagnosis, it shows its advantages, and the lesion site is very sensitive, the image is also very clear.
Nuclear magnetic **** vibration imaging research, a cutting-edge subject is the function of the human brain and advanced thinking activities for the study of functional nuclear magnetic **** vibration imaging. People already know a lot about brain organization, but little is known about how the brain works and why it has such advanced functions. Bell Labs in the United States in 1988 began research in this area, the U.S. government also identified the 1990s as the "decade of the brain". With nuclear magnetic **** vibration technology can be directly on the living organism for observation, and the object being measured conscious, but also has no radiation damage, imaging speed, high spatial and temporal resolution (can be up to 100 μm and dozens of ms, respectively), can detect a variety of nuclides, chemical shifts have the advantage of selectivity and so on. The U.S. Hospital of Wisconsin has taken thousands of live images of the human brain at work, and is expected to unravel the mysteries of the human brain at work in the near future.
If the frequency variations of NMR*** vibration are increased to two or more, two-dimensional or multi-dimensional NMR*** vibration can be realized, thus obtaining more information than one-dimensional NMR*** vibration. At present, the application of nuclear magnetic **** vibration imaging is limited to the hydrogen nucleus, but from the practical application of the need, but also requires that some other nuclei such as: C13, N14, P31, S33, Na23, I127, etc. nuclear magnetic **** vibration imaging. C13 has entered the practical stage, but still need to be further expanded and in-depth. The combination of nuclear magnetic **** vibration and other physical effects such as the Musburger effect (γ-ray absorption effect without recoil **** vibration), electron spin **** vibration, etc. can obtain more valuable information, both theoretically and in practical applications are of great significance. Nuclear magnetic *** vibration has a wide range of application prospects, accompanied by pulse Fourier technology has made a breakthrough, so that the C13 spectrum into the application of the stage, there is reason to believe that the spectra of other nuclei into the application of the stage should not be far away.
On the other hand, medical scientists have found that hydrogen atoms in water molecules can produce nuclear magnetic **** vibration phenomenon, the use of this phenomenon can be obtained from the distribution of water molecules in the body of information, so as to accurately map the internal structure of the human body, on the basis of the theory of 1969, State University of New York, Southern Medical Center of the Medical Doctor Damadian through the measurement of nuclear magnetic **** vibration of the relaxation time of the success of the mouse Inspired by Damadian's new technique, Paul Lauterburgh, a physicist at the State University of New York at Stony Brook, developed an imaging technique based on the phenomenon of nuclear magnetic **** vibration (MRI) in 1973, and applied his equipment to successfully map the internal structure of a living clam. After Lauterpacht, MRI technology has become increasingly sophisticated and widely used as a routine medical test for the treatment and diagnosis of Parkinson's disease, multiple sclerosis and other brain and spinal lesions, as well as cancer. 2003, Paul Lauterpacht and Peter Mansfield, a professor at the University of Nottingham in the United Kingdom, were awarded the Nobel Prize in Physiology or Physiology in 2003 for their contributions to MR*** vibrational imaging. Nobel Prize in Physiology or Medicine that year. The basic principle: the human body is placed in a special magnetic field, radio frequency pulses to stimulate the hydrogen nucleus in the body, causing the hydrogen nucleus *** vibration, and absorbing energy. After stopping the radio frequency pulse, the hydrogen nucleus sends out radio signals at a specific frequency and releases the absorbed energy, which is recorded by the receiver outside the body and processed by an electronic computer to obtain an image, which is called nuclear magnetic **** vibration imaging.
Principle of nuclear magnetic **** vibration
The nuclear magnetic **** vibration phenomenon originates from the spin angular momentum of the atomic nucleus under the action of an applied magnetic field.
According to the principle of quantum mechanics, the atomic nucleus, like the electron, also has spin angular momentum, and the specific value of its spin angular momentum is determined by the spin quantum number of the nucleus, and the experimental results show that different types of nuclei with different spin quantum numbers:
The nucleus of the nucleus with an even number of masses and protons has a spin quantum number of 0
The nucleus of the nucleus with an odd number of masses. Half-integer spin quantum number
Nuclei with an even number of masses and an odd number of protons have an integer spin quantum number
So far, only nuclei with a spin quantum number equal to 1/2 can be utilized, and the nuclei that are often utilized are: 1H, 11B, 13C, 17O, 19F, 31P
. p>Because the atomic nucleus carries an electric charge, when the atomic nucleus spin, will be generated by the spin of a magnetic moment, the direction of this magnetic moment and the direction of the spin of the nucleus is the same, the size of the nucleus and the spin of the angular momentum is proportional to the atomic nucleus. The nucleus will be placed in the applied magnetic field, if the magnetic moment of the nucleus and the direction of the applied magnetic field is different, the magnetic moment of the nucleus will rotate around the direction of the external magnetic field, this phenomenon is similar to the gyroscope in the rotation process of the rotating axis of the swing, known as the into motion. This phenomenon is similar to the oscillation of the rotating axis of a gyroscope during the rotation process, which is called the in-motion. The in-motion has energy and a certain frequency.
The frequency of the atomic nucleus into action by the strength of the applied magnetic field and the nature of the atomic nucleus itself, that is to say, for a particular atom, in a certain strength of the applied magnetic field, the frequency of the atomic nucleus spin into action is fixed.
The energy of the atomic nucleus is related to the magnetic field, the magnetic moment of the nucleus, and the angle between the magnetic moment and the magnetic field, according to the principle of quantum mechanics, the magnetic moment of the nucleus and the angle between the applied magnetic field is not a continuous distribution, but by the magnetic quantum number of the nucleus is determined by the magnetic moment of the nucleus, the magnetic moment of the nucleus of the nucleus of the direction can only be in the magnetic quantum number of the jumps between the magnetic moment of the nucleus, and can not be smooth change, so that the formation of a series of energy levels. When an atomic nucleus receives energy input from other sources in an applied magnetic field, an energy level jump occurs, which means that the angle between the magnetic moment of the nucleus and the applied magnetic field changes. This energy level jump is the basis for obtaining the nuclear magnetic **** vibration signal.
In order to make the atomic nucleus spin in the progress of the energy level jump, you need to provide the atomic nucleus for the energy required for the jump, this energy is usually through the external radio frequency field to provide. According to the principle of physics, when the frequency of the applied radio frequency field and the frequency of the atomic nucleus spin progress is the same, the energy of the radio frequency field can be effectively absorbed by the atomic nucleus, for the energy level jump to provide assistance. Therefore, a particular nucleus, in a given applied magnetic field, only absorbs the energy provided by a particular frequency of the RF field, which creates a nuclear magnetic **** vibration signal.
Applications of NMR
NMR Technology
NMR Spectroscopy
NMR technology, i.e., NMR spectroscopy, is a technology that applies the phenomenon of NMR to the determination of molecular structures. For the determination of organic molecular structure, NMR spectroscopy plays a very important role, and NMR spectroscopy, together with ultraviolet spectroscopy, infrared spectroscopy and mass spectrometry, is called the "four famous spectra" by organic chemists. At present, the study of NMR spectroscopy is mainly focused on the 1H and 13C atomic nuclei.
For isolated nuclei, the same nucleus in an external magnetic field of the same strength is sensitive only to a radio-frequency field of a particular frequency. But in the molecular structure of the nucleus, due to the molecular distribution of the electron cloud and other factors, the actual felt strength of the external magnetic field tends to change to a certain extent, and is in the molecular structure of the nucleus in different positions, the felt strength of the applied magnetic field is also different, this molecular electron cloud on the strength of the applied magnetic field will lead to the molecules of different positions of the nucleus of the different frequencies of the This effect of the electron cloud in the molecule on the strength of the applied magnetic field causes the nuclei at different locations in the molecule to be sensitive to different frequencies of the radio frequency field, which leads to differences in the NMR*** vibration signals. The distribution of chemical bonds and electron clouds in the vicinity of the nucleus is known as the chemical environment of the nucleus, and the change in the frequency and position of the NMR signal due to the influence of the chemical environment is known as the chemical shift of the nucleus.
The coupling constant is another important information provided by NMR spectroscopy in addition to the chemical shift. The so-called coupling refers to the interaction of the spin angular momentum of neighboring nuclei, and the interaction of this nuclear spin angular momentum will change the distribution of energy levels of the nucleus' spin in the external magnetic field, resulting in the cleavage of the energy levels, which will cause a change of the shape of the peaks of the signal in the NMR spectrum, and the change of the shape of the peaks can be resolved by analyzing these peaks. By analyzing the changes in the shape of these peaks, the connection between the atoms in the molecular structure can be deduced.
Finally, the signal intensity is the third important information of NMR spectra. Nuclei in the same chemical environment will be displayed as the same signal peak in the NMR spectra, and by analyzing the intensity of the signal peaks, the number of these nuclei can be obtained, which will provide important information for the analysis of the molecular structure. The intensity of the peaks is characterized by the integral of the area under the curve of the peaks, which is particularly important for 1H-NMR spectra, whereas for 13C-NMR spectra, the intensity of the peaks is not very important because of the insignificant correspondence between the intensity of the peaks and the number of nuclei.
Early NMR spectra were mainly focused on hydrogen spectra because the 1H atoms capable of generating NMR signals were very abundant in nature, and the NMR signals generated by them were strong and easy to detect. With the development of Fourier transform technology, the NM***Vibrometer can simultaneously emit radiofrequency fields of different frequencies within a short period of time, so that repeated scans of the sample can be performed to distinguish the weak NM***Vibrometry signals from the background noise, which makes it possible to collect the 13C NM***Vibrometry signals.
In recent years, two-dimensional NM**** vibrational spectroscopy has been developed, which allows one to obtain more information about the structure of the molecule, and two-dimensional NM**** vibrational spectroscopy is now capable of resolving the spatial structure of protein molecules with small molecular weights.
MRI technology
Nuclear magnetic **** vibration imaging
Nuclear magnetic **** vibration imaging technology is the application of nuclear magnetic **** vibration in the medical field. The human body contains very rich water, different organizations, the water content varies, if you can detect the distribution of these water information, you can draw a more complete image of the internal structure of the human body, nuclear magnetic **** vibration imaging technology is through the identification of water molecules in the distribution of hydrogen atoms in the distribution of signals to speculate on the distribution of water molecules in the body, and then detect the internal structure of the human body's technology.
Unlike the NMR***Vibration Spectroscopy technique used to identify the molecular structure, the NMR***Vibration Imaging technique adapts the strength of the applied magnetic field rather than the frequency of the radio frequency field. Nuclear magnetic **** vibration imaging instrument in the direction perpendicular to the main magnetic field will provide two mutually perpendicular gradient magnetic field, so that the distribution of the magnetic field in the human body will change with the change of spatial location, each location will have a different intensity, direction of the magnetic field is different, so that hydrogen atoms located in different parts of the human body will react to different radio frequency field signals, through the recording of this reaction, and computational processing. Information about the distribution of water molecules in space can be obtained, thus obtaining an image of the internal structure of the human body.
Nuclear magnetic **** vibration imaging technology can also be combined with X-ray tomography (CT) to provide important data for clinical diagnosis and physiological and medical research.
Nuclear magnetic **** vibration imaging technology is a non-invasive detection technology, compared with X-ray fluoroscopy and radiography, MRI has no radiation effects on the human body, compared with ultrasound detection technology, nuclear magnetic **** vibration imaging is more clear, can show more details, in addition, compared with other imaging technologies, nuclear magnetic **** vibration imaging not only can show the tangible physical lesions, but also It is also able to accurately determine the functional responses of the brain, heart and liver. MRI technology plays a very important role in the diagnosis of Parkinson's disease, Alzheimer's disease, cancer and other diseases.
MRS technology
Nuclear magnetic **** vibration bathymetry
Nuclear magnetic **** vibration detection is an extension of MRI technology in the field of geological exploration, through the detection of water distribution information in the strata, you can determine whether there is groundwater under a certain stratum, the height of the water table, the water content of the aquifer and porosity and other information on stratigraphic structure.
At present, MRS technology has become a complementary means of traditional drilling detection technology and is applied in the prevention of geological disasters such as landslides, but compared with traditional drilling detection, the purchase, operation and maintenance costs of MRS equipment are very high, which seriously restricts the application of MRS technology in geoscience.
Characteristics of nuclear magnetic **** vibration
①*** vibration frequency is determined by the structure of the electrons outside the nucleus and the nuclear nearest-neighbor grouping; ② the strength of the **** vibration peaks is determined by the proportion of this grouping in the alloy; ③ the resolution of the spectral lines is very high.
Advantages of magnetic **** vibration imaging
Compared with ordinary X-rays, which won the Nobel Prize for Physics in 1901, or computerized tomography (CT), which won the Nobel Prize for Medicine in 1979, the biggest advantage of magnetic **** vibration imaging is that it is one of the few safe methods that do not cause any harm to the human body, It is a safe, fast and accurate clinical diagnostic method that does not cause any harm to the human body. Nowadays, at least 60 million cases are examined by MRI every year worldwide.
No free radiation damage to the human body;
A variety of parameters can be used for imaging, and multiple imaging parameters can provide a wealth of diagnostic information, which makes medical diagnosis and the study of metabolism and function in the human body convenient and effective. For example, the T1 values of hepatitis and cirrhosis become larger, while the T1 values of hepatocellular carcinoma are even larger, and T1-weighted images can be made to distinguish benign tumors from malignant tumors in the liver;
The desired profile can be freely selected by adjusting the magnetic field.
The magnetic field can be freely selected by adjusting the magnetic field, and the images of the parts that are inaccessible or difficult to access can be obtained by other imaging techniques. For intervertebral discs and spinal cord, sagittal, coronal, and cross-sectional imaging can be performed to visualize nerve roots, spinal cord, and ganglia. Can obtain three-dimensional images of the brain and spinal cord, unlike CT (can only obtain perpendicular to the long axis of the human body) layer by layer scanning and may miss the lesion;
Can diagnose cardiac lesions, CT due to the slow speed of scanning is difficult to perform;
The soft tissues have excellent resolution. It is superior to CT for bladder, rectum, uterus, vagina, bones, joints, and muscles;
In principle, all nuclear elements with non-zero spin can be used for imaging, e.g., hydrogen (1H), carbon (13C), nitrogen (14N and 15N), and phosphorus (31P).