The most commonly used nucleus for MAGNETIC ****VIBRATION is the hydrogen nucleus, the proton (1H), because it has the strongest signal and is widely present in human tissues. Factors affecting magnetic **** vibration imaging 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 the magnetic **** vibration, and less brightness when the signal of the magnetic **** vibration is weak, ranging from white, to gray, to black.
Various tissue magnetic *** vibration image gray scale characteristics are as follows: adipose tissue, cancellous bone is white; cerebrospinal cord, bone marrow is white-gray; viscera, muscle is gray-white; liquid, 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 blood vessels easy to separate from soft tissue. 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 shows up as a white, strongly signaling structure.
Magnetic **** vibration (MRI) has been used to image and diagnose systems throughout the body. The best results are the cranial brain, and its spinal cord, the heart large blood vessels, joints bones, soft tissues and pelvis. For cardiovascular diseases, it can not only observe the anatomical changes of the chambers, great vessels and valves, but also make ventricular analysis, qualitative and semi-quantitative diagnosis, and can make multiple cross-sectional maps, with high spatial resolution, displaying the whole picture of the heart and lesions, and their relationship with the surrounding structures, which is superior to other X-ray imaging, two-dimensional ultrasound, nuclide and CT examination. In the diagnosis of cerebral spinal cord lesions, coronal, sagittal and cross-sectional images can be made.
MRI not only provides more information than many other imaging techniques in medical imaging, but is also different from existing imaging techniques, so it has a great potential superiority for the diagnosis of disease. 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.MRI is very effective in detecting common cranio-cerebral disorders, such as intracerebral hematomas, extracerebral hematomas, brain tumors, intracranial aneurysms, arterial and venous vascular malformations, cerebral ischemia, intradural tumors, spinal cavernous disease, and hydrocephalus, etc. It is also effective in detecting lumbar spine, and in detecting lumbar vertebrae. It is also effective in the diagnosis of lumbar intervertebral disc posterior protrusion, primary liver cancer and other diseases.
The purpose of the examination: cranial brain and spinal column, spinal cord lesions, diseases of the five senses, heart disease, mediastinal mass, bone and joint and muscle lesions, uterus, ovary, bladder, prostate, liver, kidney, pancreas and other parts of the lesions.
Advantages:
1. MRI has no ionizing radiation damage to the human body;
2. MRI can obtain native three-dimensional cross-sectional imaging without the need for reconstruction to obtain multi-directional images;
3. The soft tissue structure is clearly shown on the central nervous system, the bladder, rectum, uterus, vagina, joints, muscles, and other checks are better than the CT.
4. Multi-sequence Imaging, a variety of image types, to clarify the nature of the lesion to provide richer imaging information.
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 obtain diagnosis of both imaging and pathology;
2. The examination of the lungs is not superior to X-ray or CT, and the examination of liver, pancreas, adrenal glands, and prostate gland is not superior to CT, but the cost is much higher;
3. lesions of the gastrointestinal tract are not as good as endoscopy;
4. diagnosis of bone fractures is less sensitive than CT and X-ray radiographs;
5. people with metal objects in their bodies should not undergo MRI.
6. critically ill patients should not undergo it.
7. people in their third trimester of pregnancy are not recommended to undergo MRI unless it is necessary.
8. People with pacemakers should not undergo MRI or be near the MRI equipment
9. Most MRI equipment has a closed examination space, and some patients are unable to cooperate with the examination due to fear
10. The examination takes a long time
Cautions
Because of the strong magnetic fields in the MRI machine and MRI room, patients with pacemakers should not undergo MRI unless they have a pacemaker. Generally in hospitals, outside the door of the nuclear magnetic *** vibration examination room, there are red or yellow eye-catching signs indicate that absolutely strictly prohibited to carry out the nuclear magnetic *** vibration examination of the situation.
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.
MRI is a powerful and powerful magnetic field that can be used for a variety of purposes.
MRI
In recent years, with the progress and development of science and technology, there are many orthopedic internal fixation, especially for 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 titanium-made internal fixators are expensive, which to some extent affects its popularization.