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Nuclear Magnetic Resonance Imaging in longitudinal sections of the human brainNuclear Magnetic Resonance Imaging, or NMRI, is a technique that uses nuclear magnetic *** vibration (NMRI), or also known as spin NMRI, also known as spin imaging, or magnetic resonance imaging (MRI), utilizes the principle of nuclear magnetic resonance (NMR), which is based on the different attenuation of the released energy in different structural environments within a substance, and is performed by means of an external gradient magnetic field. The electromagnetic waves emitted by the external gradient magnetic field detection, you can know the location and type of atomic nuclei constituting this object, according to which the internal structure of the object can be drawn into the image.
Using this technique to image the internal structure of the human body produces a revolutionary medical diagnostic tool. The application of rapidly changing gradient magnetic fields has greatly accelerated the speed of nuclear magnetic **** vibration imaging, making the application of this technology in clinical diagnosis and scientific research a reality, and greatly promoting the rapid development of medicine, neurophysiology and cognitive neuroscience.
From the discovery of the phenomenon of nuclear magnetic **** vibration to the maturity of MRI technology in this period of several decades, the field of research on nuclear magnetic **** vibration in three fields (physics, chemistry, physiology or medicine) has been awarded six Nobel Prizes, which is sufficient to illustrate the importance of this field and its derived technology.
Table of Contents [Hidden]
1 Physical Principles
1.1 Overview of the Principles
1.2 Mathematical Operations
2 System Components
2.1 NMR Experimental Setup
2.2 Components of an MRI System
2.2.1 Magnet System
2.2.2 RF System
2.2.3 Computerized Image Reconstruction System
2.3 Basic Methods of MRI
3 Technical Applications
3.1 Applications of MRI in Medicine
3.1.1 Overview of Principles
3.1.2 Advantages of Magnetic **** Vibration Imaging
3.1.3 Disadvantages of MRI and Possible Hazards
3.2 Applications of MRI in Chemistry
3.3 Other Advances in Magnetic **** Vibration Imaging
4 Contributions of the Nobel Laureates
5 Future Perspectives
6 Related Entries
6.1 Preparation for Magnetization
6.2 Methods of Imaging
6.3 Medical-physiological applications
7 References
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Physical principles
An animation of a continuous slice of the human brain obtained by a magnetic **** vibrational imaging scan, starting at the top of the head and continuing to the base. [edit]
Overview of principles
Magnetic **** vibration imaging is a biomagnetism nuclear spin imaging technique that has developed rapidly with the development of computer technology, electronic circuitry, and superconductor technology. Doctors take into account the patient's fear of "nuclear", so often this technology is called magnetic **** vibration imaging. It is the use of magnetic fields and radiofrequency pulses to make the human tissue into the movement of the hydrogen nucleus (i.e., H +) chapter action to produce radiofrequency signals, computer processing and imaging.
Atomic nucleus in motion, absorption and atomic nucleus in motion frequency of the same radio frequency pulse, that is, the frequency of the applied alternating magnetic field is equal to the Larmor frequency, the atomic nucleus on the occurrence of *** vibration absorption, after removing the radio frequency pulse, the atomic nucleus of the magnetic moment and the absorbed energy in the form of part of an electromagnetic wave emitted, known as *** vibration emission. The process of *** vibration absorption and *** vibration emission is called "nuclear magnetic *** vibration".
The "nucleus" of MRI refers to the nucleus of the hydrogen atom, because the human body is made up of about 70% water, and MRI relies on hydrogen atoms in water. When an object is placed in a magnetic field, it is irradiated with the appropriate electromagnetic waves to make it *** vibrate, and then the electromagnetic waves it releases are analyzed to learn the location and type of nuclei that make up the object, from which precise three-dimensional images of the object's interior can be drawn.
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Mathematical operations
The atomic nucleus is positively charged and has a spin motion, and its spin motion is bound to produce a magnetic moment, called the nuclear magnetic moment. Studies have shown that the nuclear magnetic moment μ is proportional to the spin angular momentum S of the nucleus, that is
The formula γ is the scale factor, known as the atomic nucleus of the spin ratio. In the external magnetic field, the spatial orientation of the nuclear spin angular momentum is quantized, and its projection in the direction of the external magnetic field can be expressed as
m is the nuclear spin quantum number. Based on the relationship between the nuclear magnetic moment and the spin angular momentum, the orientation of the nuclear magnetic moment in the external magnetic field is also quantized, and its projection in the direction of the magnetic field can be expressed as
For different nuclei, m is taken as an integer or half-integer, respectively. In the external magnetic field, the nucleus with magnetic moment has the corresponding energy, the value of which can be expressed as
Where B is the magnetic induction strength. It can be seen that the energy of the nucleus in the external magnetic field is also quantized. Due to the interaction of magnetic moment and magnetic field, the spin energy is split into a series of discrete energy levels, the difference between two adjacent energy levels ΔE = γhB. irradiation of the nucleus with the appropriate frequency of electromagnetic radiation, if the electromagnetic radiation photon energy hν is exactly the difference between the two adjacent nuclear energy levels ΔE, then the nucleus will absorb this photon, the occurrence of the nuclear magnetism*** vibration of the frequency conditions are:
In the formula ν is the frequency, ω is the angular frequency. For a definite nucleus, the spin ratio γ can be determined precisely. It can be seen that by determining the frequency ν of the radiated field at the time of nuclear magnetic *** vibration, the magnetic induction can be determined; conversely, if the magnetic induction is known, the frequency of nuclear *** vibration can be determined.
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System composition
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NMR experimental setup
The nuclear magnetic **** vibration is achieved by using the method of adjusting the frequency. Electromagnetic waves are emitted from a coil to the sample, and the modulating oscillator serves to continuously vary the frequency of the RF electromagnetic waves around the sample **** vibration frequency. When the frequency coincides with the nuclear magnetic *** vibration frequency, the output of the radio frequency oscillator will appear an absorption peak, which can be displayed on the oscilloscope, at the same time by the frequency meter instantly read out the value of *** vibration frequency at this time. Nuclear magnetic *** vibration spectrometer is specially used to observe the nuclear magnetic *** vibration of the instrument, mainly by the magnet, probe and spectrometer three major components. The function of the magnet is to produce a constant magnetic field; probe placed between the magnetic poles, used to detect the nuclear magnetic *** vibration signal; spectrometer is the *** vibration signal amplification and processing and display and record down.
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Components of an MRI system
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Magnet system
Static magnetic field: superconducting magnets currently used in clinical practice, with field strengths ranging from 0.5 to 4.0 T, with 1.5 T and 3.0 T being common, and shim coils to assist in achieving a high degree of uniformity.
Gradient field: Used to generate and control the gradient in the magnetic field for spatial encoding of the NMR signal. This system has three sets of coils that generate gradient fields in the x, y, and z directions, and the magnetic fields of the coil sets are superimposed to obtain gradient fields in any direction.
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Radiofrequency system
Radiofrequency (RF) generator: generates a short, strong RF field, which is applied to the sample in pulses, causing the hydrogen nuclei in the sample to produce NMR phenomena.
Radio Frequency (RF) Receiver: Receives the NMR signal, amplifies it and enters the image processing system.
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Computer image reconstruction system
Signals sent by the RF receiver are converted to mathematical signals by an A/D converter, and according to the correspondence with the various voxels of the observation level, they are processed by a computer to produce the level image data, which is then converted by a D/A converter, and added to an image monitor, which displays images of the desired level of observation according to the magnitude of the NMR in different gray scale The image of the desired observation level is displayed in different gray levels according to the size of the NMR.
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Basic methods of MRI
Selective gradient field Gz
Phase coding and frequency coding
Image reconstruction
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Technical applications
3D MRI[edit]
Medical applications of MRI
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Overview of the principle
Hydrogen nuclei are the preferred nuclei for imaging the human body: various tissues in the human body contain a large amount of water and hydrocarbons, so the NMR*** vibration of the hydrogen nuclei is highly flexible and the signal is strong, which is the reason why hydrogen nuclei are preferred as an imaging element in the human body.The intensity of the NMR signal is related to the density of hydrogen nuclei in the sample, and the proportion of water contained in the human body is different between the various tissues, i.e., the ratio of the number of hydrogen nuclei is different. NMR signal intensity is different from the number of hydrogen nuclei in the human body, using this difference as a characteristic quantity to separate various tissues, which is the NMR **** vibration image of the density of hydrogen nuclei. Between different tissues of the human body, normal tissue and the lesion tissue in that tissue between the hydrogen nuclei density, relaxation time T1, T2 three parameters of the difference, is MRI used for clinical diagnosis of the most important physical basis.
When a radiofrequency pulse signal is applied, the hydrogen nucleus changes its nuclear state, and after the radiofrequency has passed, the hydrogen nucleus returns to its initial energy state, and the electromagnetic wave generated by the *** vibration is emitted. Small differences in the vibration of the nucleus can be accurately detected, and after further computer processing, it is possible to obtain a three-dimensional image of the chemical composition of the reactive tissue, from which we can obtain information that includes differences in the water content of the tissue as well as the movement of water molecules. In this way, pathological changes can be recorded.
2/3 of the body's weight is water, and such a high percentage is the basis for magnetic **** vibration imaging to be widely used in medical diagnostics. The water in organs and tissues in the human body is not the same, and the pathological process of many diseases can lead to changes in the water pattern, which can be reflected by the magnetic **** vibration image.
The images obtained by MRI are very clear and detailed, which greatly improves the diagnostic efficiency of doctors and avoids the need for a thoracotomy or cesarean section for diagnostic surgery. Because MRI does not use harmful X-rays and allergy-inducing contrast agents, there is no damage to the human body.
MRI can be used to image various parts of the human body from multiple angles and planes, with high resolution, and can more objectively and concretely display anatomical tissues and neighboring relationships within the body, allowing for better localization and characterization of the lesions. It is of great value for the diagnosis of systemic diseases, especially for the diagnosis of early tumors.
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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, fast, and reliable 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 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, which can get the images of the parts that are inaccessible or difficult to access 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).
Magnetic **** vibration imaging of human abdominal coronal sections[edit]
Disadvantages and possible hazards of MRI
While MRI is not fatal to the patient, it still causes some discomfort to the patient. Necessary measures should be taken to minimize this negative impact before MRI diagnosis. The main disadvantages are:
Like CT, MRI is an anatomical imaging diagnosis, and many lesions are still difficult to diagnose by MRI alone, unlike endoscopy, which can obtain both imaging and pathologic diagnosis;
The examination of the lungs is not superior to that of X-rays or CT, and the examination of the liver, pancreas, adrenal glands, and prostate gland is no better than that of CT, but it costs much higher;
More importantly, it can be used as a diagnostic tool in the treatment of cancer.
It is not as good as endoscopy for gastrointestinal lesions;
The scanning time is long and the spatial resolution is not good enough;
Because of the strong magnetic field, MRI can not be applied to special patients, such as those who have a magnetic metal in the body or a pacemaker.
Factors that may cause harm from MRI systems include the following:
Strong static magnetic fields: in the presence of ferromagnetic material, either embedded in the patient's body or within the range of the magnetic field, can be a risk factor;
Time-varying gradient fields: can be induced in subjects to produce electric fields that excite nerves or muscles. Peripheral nerve excitation is the upper indicator of the safety of gradient fields. At sufficient intensity, peripheral nerve excitation (such as tingling or percussion) can be produced, and even cardiac excitation or ventricular fibrillation can be induced;
Thermogenic effects of radiofrequency (RF) fields: The large-angle RF fields used in MRI focusing or measurement processes emit electromagnetic energy that is converted to heat in the patient's tissues, causing the tissue temperature to rise.
The thermogenic effects of RF need to be further explored, and the clinical scanner has a so-called thermogenic effect on the amount of RF energy. The thermogenic effect of RF needs to be further explored, and the clinical scanner has the so-called "specific absorption rate" (SAR) limitation for RF energy;
Noise: The various noises generated during the operation of MRI may cause hearing damage in some patients;
Toxicity and side-effects of contrast agents : the contrast agents currently in use are mainly gadolinium-containing compounds, with a side-effect incidence of 2%-4%.
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Applications of MRI in chemistry
The application of MRI in chemistry is not as extensive as in medicine, mainly because of technical difficulties and difficulties with imaging materials, and is currently used in the following areas:
In the field of polymer chemistry, such as the study of carbon-fiber-reinforced epoxy resins, the study of spatial solid-state reaction directionality study, study of solvent diffusion in polymers, polymer vulcanization and homogeneity study of elastomers, etc.;
In metal ceramics, to detect the presence of sand holes in ceramic products through the study of porous structure;
In rocket fuels, for the detection of defects in the solid fuel as well as the distribution of fillers, plasticizers, and propellants;
In petrochemistry In petrochemistry, the main focus is on the study of the distribution state and circulation of fluids in rocks as well as the study of reservoir description and enhanced oil recovery mechanisms.
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Other advances in magnetic **** vibration imaging
Nuclear magnetic **** vibration analysis technique is to analyze the molecular structure and properties of a substance through the determination of characteristic parameters of nuclear magnetic **** vibration spectral lines (e.g., spectral line widths, shape of spectral line profiles, spectral line areas, and positions of spectral lines, etc.). It can be a completely non-destructive detection method without destroying the internal structure of the sample under test. At the same time, it has a very high resolution and accuracy, and can be used for the measurement of the nucleus is also more, all of which are better than other measurement methods. Therefore, nuclear magnetic **** vibration technology has gained wide application in physics, chemistry, medicine, petrochemistry, archaeology and so on.
Magnetic *** vibration microscopy (MR microscopy, MRM/μMRI) is a slightly later development of MRI technology, MRM highest spatial resolution is 4 μm, can be close to the level of the general optical microscope like. MRM has been very commonly used as an animal model of disease and drug research.
In vivo MR spectroscopy (MRS) is the ability to determine the NMR spectrum of a specific part of an animal or a human body in order to directly identify and analyze its chemical composition.
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Contributions of Nobel laureates
On October 6, 2003, the Karolinska Institutet School of Medicine in Sweden announced that the 2003 Nobel Prize in Physiology or Medicine had been awarded to American chemist Paul C. Lauterbur and British physicist Peter Mansfield Mansfield for their groundbreaking achievements in the field of nuclear magnetic **** vibrational imaging techniques used within the field of medical diagnosis and research.
Lauterburgh's contribution was the introduction of gradients into a magnetic field by attaching an inhomogeneous magnetic field within the main magnetic field, thus creating a visual two-dimensional structural image of the internal structure of matter that is not visible using other technical means. He described how a gradient magnet could be added to the main magnet, and then cross sections of test tubes filled with ordinary water immersed in heavy water could be seen. There is no other imaging technique that can distinguish images between ordinary water and heavy water. By introducing a gradient magnetic field, it is possible to change the frequency of the nuclear magnetic **** vibration electromagnetic waves point by point, and by analyzing the emitted electromagnetic waves, it is possible to determine the source of the signal.
Mansfield further developed the theory concerning the use of additional gradient magnetic fields in stable magnetic fields, advancing their practical application. His discovery of a mathematical analysis of magnetic **** vibration signals laid the groundwork for moving the method from theory to application. This led to magnetic ****vibration imaging becoming a realistic and viable method of clinical diagnosis a decade later. He utilized gradients in the magnetic field to more accurately show differences in *** vibration. He demonstrated how to effectively and rapidly analyze detected signals and convert them into images. Mansfield also proposed that extremely rapid gradient changes could yield instantaneous images, a technique known as planar echo-planar imaging (EPI), which became the mainstay of functional magnetic *** vibration imaging (functional MRI, fMRI) research that began to flourish in the 1990s.
Raymond Damadian's "Devices and Methods for the Detection of Cancerous Tissues" is noteworthy for the groundbreaking contributions to the theory of superconductors and superfluids made by the 2003 Nobel Laureates in Physics, which provided the theoretical basis for the development of the fMRI scanner by two of the scientists who were awarded the 2003 Nobel Prize in Physiology or Medicine. vibrational scanners, which provided the theoretical foundation that paved the way for nuclear magnetic **** vibrational imaging technology. As a result of their theoretical work, breakthroughs in MR*** vibration imaging technology have been made, making high-resolution images of the body's internal organs possible.
In addition, a full-page advertisement from Fonar appeared simultaneously in the New York Times and the Washington Post on October 10, 2003: "Raymond Damadian, who should share the 2003 Nobel Prize in Physiology or Medicine. Without him, there would have been no nuclear magnetic **** vibration imaging." The accusation that the Nobel Prize committee had "falsified history" was widely disputed. In fact, the ownership of the invention of MRI has been debated for many years and is quite hotly contested. In the academic world, Damadian is seen as more of a businessman than a scientist.
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Future prospects
How the human brain thinks has always been a mystery. And it's an important topic of concern for scientists. And functional brain imaging using MRI helps us to study the human mind at the in vivo and holistic level. One of the best samples is the study on whether the hands of blind children can replace their eyes. Normal people can see the blue sky and blue water, and then form images in the brain to form a mood, and the blind child who has never seen the world, can touch the words with his hands, and the words tell him about the world, can the blind child also "see" it? Through functional MRI, experts scan the brains of normal and blind children, and find that blind children also have good activation areas in the visual cortex of the brain, just like normal people. From this, we can tentatively conclude that blind children through cognitive education, the hand can replace the eyes "see" the outside world.
The research and application of fast scanning technology will shorten the scanning time of patients by classical MRI imaging methods from several minutes or ten minutes to a few milliseconds, so that the effect of organ movement on the image is negligible; MRI blood flow imaging, using the flow-vacancy effect to make the morphology of blood vessels on the MRI image distinctly, making it possible to measure the direction of the flow of blood in the blood vessels and the flow rate; MRI spectral analysis can use a high magnetic field to analyze the blood flow in the blood vessels and the blood flow rate of the blood vessels. Spectral analysis can use high magnetic fields to achieve the human body's local tissue spectral analysis technology, thus increasing the information to help diagnosis; brain function imaging, the use of high magnetic field **** vibration imaging to study the function of the brain and its mechanism of occurrence is the most important topic in brain science. There is reason to believe that MRI will develop into a thought reader.
The mid-20th century to the present, information technology and life sciences is the development of the two most active areas, experts believe that, as a combination of these two MRI technology, continue to micro and functional examination on the development of the mystery of life will play a greater role in revealing.
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Related entries
Nuclear magnetic **** vibration
Radiofrequency
Radiofrequency coils
Gradient magnetic fields
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Magnetization preparation
Inversion recovery
Saturation reply ( Saturation recovery
Driven equilibrium
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Imaging methods
Spin echo
Gradient echo
Parallel imaging parallel imaging)
Echo-planar imaging (EPI)
steady-state free precession imaging (SSFP)
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Medical Physiological applications
Magnetic resonance angiography (MR angiography)
Magnetic resonance cholangiopancreatography (MR cholangiopancreatogram, MRCP)
Diffusion-weighted image (DRI)
Diffusion tensor image ( diffusion tensor image)
perfusion-weighted image
functional MRI, fMRI
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References
Fu Jieqing < Nuclear magnetic **** vibration - a scientific topic with the highest number of Nobel Prizes〉《Nature Magazine》, 2003, (06):357-261
Bie Yeh-Guang and Lv Hua 《Re-talking about nuclear magnetic **** vibration in medicine〉《Physics and Engineering》, 2004, (02):34, 61
Jin Yong-Jun, the founder of fMRI, has been working on the development of fMRI for the past few years. p>
Jin Yongjun and Ai Yanbao, "NMR***Vibration Technology and Applications" Physics and Engineering, 2002, (01):47-48, 50
Liu Donghua, Li Xianyao, and Sun Zhaohui, "NMR***Vibration Imaging" University Physics, 1997, (10):36-39, 29
Ruan Ping, "NMR***Vibration Imaging and Its Medical Applications" Guangxi Physics, 1999, (10):34-35, 29
Ruan Ping, "NMR***Vibration Imaging and Its Medical Applications" Guangxi Physics, 1999, (11):34, 57
Lauterbur P C Nature, 1973, 242:190
Wei-Hua Huang, 〈Approach to NMR***Vibration〉Medicine and Health Care, 2004, (03):15
Chaohui Ye, 〈New Advances in Magnetic ****Vibration Imaging〉Physics, 2004, (01):17-17, 30
Wei-Hua Huang, 〈NMR***Vibration Imaging and Its Medical Applications 2004, (01):12-17
Jianguang Tian, Buyli Liu, Zhaofan Xia, and Zhaohui Ye, "Safety of Magnetic *** Vibration Imaging," Journal of Spectroscopy, 2002, (06):505-511
Zijiang Jiang, "Application of Nuclear Magnetic *** Vibration Imaging NMRI in Chemistry," Chemistry World, 1995, (11):563-565
New Progress in Magnetic *** Vibration Imaging. 565
Fan Qingfu (Nuclear Magnetic **** Vibration Imaging and the Nobel Prize) Shanghai Biomedical Engineering, 2003, (04):cover 3
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