Nuclear magnetic **** vibration is a physical phenomenon, as a means of analysis is widely used in physics, chemistry biology and other fields, until 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 (MR).
MR 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 signal generated, detected with a detector and input into the computer, after the processing of the converted images displayed on the screen.
The amount of information provided by MR is not only greater than 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 in CT detection; does not require injection of contrast media; 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 hydrocephalus.
MR 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 MR, which is also expensive.
Magnetic **** vibration imaging is a kind of tomography, it uses the magnetic **** vibration phenomenon from the human body to obtain electromagnetic signals, and reconstruction of the human body information. 1946 Stanford University's Flelix Bloch and Harvard University's Edward Purcell independently of each other to discover the phenomenon of nuclear magnetic **** vibration. Magnetic **** vibration imaging is based on this physical phenomenon. 1972 Paul Lauterbur developed a method of spatial coding of nuclear **** vibration signals, which can be used to reconstruct images of the human body.
Magnetic **** vibration imaging and other tomographic techniques (such as CT) have some **** the same point, for example, they can show the distribution of a certain physical quantity (such as density) in space; also has its own characteristics, magnetic **** vibration imaging can be obtained in any direction of the tomographic image, three-dimensional body image, and even can get the spatial - spectral distribution of the four-dimensional image.
Like PET and SPET, the magnetic **** vibration signal used for imaging comes directly from the object itself, and it can be said that magnetic **** vibration imaging is also a kind of emission tomography. However, unlike PET and SPET, magnetic **** vibration imaging does not require the injection of radioisotopes for imaging. This fact also makes the magnetic **** vibration imaging technique safer.
From the magnetic **** vibration image, we can get a variety of physical properties of the material parameters, such as proton density, spin-lattice relaxation time T1, spin-spin relaxation time T2, diffusion coefficient, magnetization coefficient, chemical shifts and so on. Compared with other imaging techniques (e.g. CT ultrasound PET, etc.), magnetic **** vibration imaging is more diverse, the imaging principle is more complex, and the information obtained is more abundant. Therefore, magnetic **** vibration imaging has become a popular research direction in medical imaging.
Nuclear magnetic **** vibration imaging principle: the atomic nucleus is positively charged, and the atomic nuclei of many elements, such as 1H, 19FT and 31P, carry out spin motion. Normally, the arrangement of the spin axis of the nucleus is irregular, but when placed in an applied magnetic field, the nuclear spin space orientation transitions from disorder to order. The magnetization vector of the spin system grows gradually from zero, and when the system reaches equilibrium, the magnetization strength reaches a stable value. If the nuclear spin system is subjected to external effects, such as a certain frequency of radio frequency excitation of the nucleus can cause *** vibration effect. In the radio frequency pulse stops, the spin system has been excited nuclei, can not maintain this state, will return to the magnetic field in the original arrangement of the state, at the same time release a weak energy, become radio signals, the many signals detected, and make it possible to carry out the spatial resolution, you get the distribution of atomic nuclei in the movement of the image. Atomic nuclei from the excited state back to the equilibrium arrangement of the process called relaxation process. The time required for it is called relaxation time. There are two types of relaxation time i.e. T1 and T2, T1 is spin-dot array or longitudinal relaxation time T2 and T2 is spin-spin or transverse relaxation time.
The most commonly used nucleus for magnetic **** vibration is the hydrogen nucleus proton (1H) because it has the strongest signal and is also widely present in human tissues. Factors affecting the magnetic ****vibration image include (a) the density of the proton, (b) the length of the relaxation time, (c) the flow of blood and cerebrospinal fluid, (d) paramagnetic substances (e) proteins. The gray scale of a magnetic **** vibration image is characterized by greater brightness the stronger the signal of magnetic **** vibration, and less brightness when the signal of magnetic **** vibration is weak, ranging from white, gray to black. Various tissue magnetic *** vibration image gray scale characteristics are as follows; adipose tissue, cancellous bone is white; cerebral spinal cord, bone marrow is whitish-gray; viscera, muscle is grayish-white; liquids, the normal rate of flow of blood is black; bone cortex, gas, air-containing lungs is black.
Nuclear magnetic **** vibration of another feature is the flow of liquid does not produce a signal called the flow effect or flow blanking effect. Thus blood vessels are grayish-white tubular structures, while blood is signal-free black. This makes the blood vessels easily soft tissue separated. The normal spinal cord is surrounded by cerebrospinal fluid, which is black, and has white dura mater lined with fat so that the spinal cord appears as a white, strong signal structure. MRI*** vibration has been applied to diagnostic imaging of systems throughout the body. The best results are the cranial brain, and its spinal cord, cardiac blood vessels, joints and bones, soft tissues and pelvic cavity. For cardiovascular disease can not only observe the anatomical changes of the chambers, great vessels and valves, but also make ventricular analysis, qualitative and semi-quantitative diagnosis, can be made for multiple cross-sectional maps, high spatial resolution, showing the whole picture of the heart and the lesion and its relationship with the surrounding structures, is superior to other X-ray imaging, two-dimensional ultrasound, nuclide and CT examination. Coronal, sagittal, and cross-sectional images can be made in the diagnosis of cerebrospinal lesions.
The purpose of the examination: cranial brain and spinal column, spinal cord lesions, pentacameral diseases, cardiac diseases, mediastinal masses, bone joint and muscle lesions, uterus, ovaries, bladder, prostate, liver, kidneys, pancreas, and other parts of the lesions.
Advantages:
1. MRI has no damage to the human body;
2. MRI can obtain three-dimensional images of the brain and spinal cord, unlike CT, which scans one layer at a time and may miss lesions;
3. It can diagnose cardiac pathology, which is difficult to perform due to the slow speed of CT scanning;
4. It is better than CT in the examination of the bladder, rectum, uterus, vagina, bones and joints, muscles and other parts of the body,
Disadvantages:
1. Like CT, MRI is also a diagnostic imaging, and many lesions are still difficult to diagnose by MRI alone, unlike endoscopy, which can be used to obtain diagnosis of both imaging and pathology at the same time;
2. The examination of lungs is not superior to the examination of X-rays or CT, and the examination of liver, pancreas, adrenal glands, and prostate is not superior to CT, but the cost is much higher;
3. Much more expensive;
3. Not as good as endoscopy for lesions in the gastrointestinal tract;
4. People with metal objects left in the body should not undergo MRI.
5. Critically ill patients can not be done
6. Pregnant for 3 months
7. With a pacemaker
Nuclear Magnetic **** vibration examination of the precautions
Because of the very strong magnetic field in the MRI machine and the MRI room, it is absolutely forbidden to perform MRI for pacemakers, or for those who have metal clips or metal stents after vascular surgery, or for those who have undergone metal stent surgery on coronary arteries, esophagus, prostate, or bile ducts, or the metal may be attracted to move by the strong magnetic field, which could have serious consequences and lead to life-threatening situations. Otherwise, due to the movement of metal attracted by the strong magnetic field, it will produce serious consequences that may lead to life-threatening. Generally, outside the door of the hospital's MRI room, there is a red or yellow sign indicating that MRI is strictly prohibited.
The body can not remove other metal foreign body, such as metal internal fixation, artificial joints, metal dentures, stents, silver clips, shrapnel and other metal deposits, for the examination of the relative contraindication, must be examined, it should be closely observed, in order to prevent the examination of the metal in a strong magnetic field in the movement of the neighboring blood vessels and important tissues, resulting in serious consequences, such as the absence of a special need to not accept the nuclear magnetism*** vibration examination. Vibration examination. The metal contraceptive ring and movable metal dentures must be taken out and then examined.
Sometimes, metallic iron ions left in the body may affect the quality of the image or even the correct diagnosis.
Before entering the nuclear magnetic **** vibration examination room, you should remove cell phones, pagers, magnetic cards, watches, coins, keys, lighters, metal belts, metal necklaces, metal earrings, metal buttons, and other metal jewelry or metal objects that you are carrying on your body. Otherwise, the uniformity of the magnetic field may be affected during the examination, resulting in interference with the image and the formation of artifacts, which is not conducive to the display of the lesions; and due to the strong magnetic field, metal objects may be sucked into the NMR*** vibration machine, thus causing damage to the very expensive NMR*** vibration machine; in addition, cell phones, pagers, magnetic cards, watches and other items may also be damaged by the strong magnetic field, which will result in the unnecessary loss of personal belongings.
In recent years, there have been a number of new developments in the field of magnetic fields.
In recent years, with the progress and development of science and technology, there are many orthopedic internal fixation, especially the internal fixation of the spine, began to be made of titanium alloy or titanium metal. Because titanium metal is not attracted by magnetic field, it will not move in the magnetic field. Therefore, patients with titanium internal fixations in their bodies are safe for MR*** vibration examinations; and titanium does not interfere with MR*** vibration images. This is valuable for patients with spinal disorders who require internal spinal fixation surgery. However, titanium alloys and internal fixation made of titanium metal are expensive, which affects its popularization to a certain extent.
Edited Words
Open Category:
Medical, Medical Imaging
References:
1. Medical Imaging Technology
Contributors:
wtrecamel, yo immobility, waterone83, sleeve swallowing qiankun xiaowuhou, dairui725
This entry was mentioned in the following entries Mentioned in:
Heroin, muscular dystrophy lateral sclerosis, primary liver cancer
Explanation of "MRI" in the English-Chinese Dictionary (Source: Baidu Dictionary):
MRI
abbr.
1. = Magnetic Resonance Imaging医磁***振影影
2. = Machine Readable Information 电脑机读able信息