What Is the Difference between an MRI and a CT Scan?
MRI is Magnetic Resonance Imaging. The full English name is: Magnetic Resonance Imaging. The nucleus often used by people are: 1H, 11B, 13C, 17O, 19F, 31P. It was called NMR imaging at the beginning of this technology. By the early 1980s, the term NMR imaging, a new medical technology, was becoming more and more familiar to the public. With the installation of large magnets, some people began to worry that the letter "N" might have a negative impact on the development of magnetic resonance imaging. In addition, the word "nuclear" could easily lead hospital staff to another association of nuclear medicine in the magnetic resonance room. Therefore, in order to highlight the advantages of this inspection technology in that it does not produce ionizing radiation, and to distinguish it from nuclear medicine using radioactive elements, radiologists and equipment manufacturers have agreed to abbreviate MRI as simply MRI ) ".
- Magnetic resonance imaging is a type of tomography, which uses magnetic resonance phenomena to obtain electromagnetic signals from the human body and reconstruct human information. 1946
- Nuclear magnetic resonance is a physical phenomenon. As an analytical method, it is widely used in the fields of physics, chemical biology, and so on. It was not used in clinical clinical testing until 1973. To avoid with
- NMR imaging principle: the atomic nucleus is positively charged, and many elements
- The most commonly used nucleus for magnetic resonance is the hydrogen atom proton (1H), because it has the strongest signal and is also widely present in human tissues. Affects magnetic resonance
- What are the clinical applications of MRI?
- The magnetic resonance imaging image is very similar to the CT image, both of which are "digital images", and show cross-sectional images of anatomy and pathology with different structures in different gray levels. Like CT, magnetic resonance imaging is also suitable for almost all diseases of the whole system, such as tumors, inflammation, trauma, degenerative diseases, and various congenital diseases.
Magnetic resonance imaging is free of bone artifacts, and can be used for direct multi-directional (transverse, coronal, sagittal, or any angle) slice. The anatomy and lesions of the brain, spine, and spinal cord are displayed better than CT. Magnetic resonance imaging can show the structure of blood vessels without the use of angiographic agents due to its "empty effect", so it shows blood vessels (except small blood vessels) "without damage" and distinguishes between tumors, lymph nodes and blood vessel structures. In terms of aspects, there are unique features. Magnetic resonance imaging has soft tissue resolution several times higher than that of CT. It can sensitively detect changes in water content in tissue components, so it can often detect lesions more effectively and early than CT. The progress made through the research of magnetic resonance blood flow imaging technology enables the measurement of blood flow and the use of blood flow gating in the living body, so that magnetic resonance imaging can clearly and comprehensively show the heart, myocardium, pericardium and other small hearts in the heart. The structure provides a reliable method for the non-destructive examination and diagnosis of various acquired and congenital heart diseases (including coronary heart disease, etc.), and the examination of cardiac function. With the research and successful application of various fast scanning sequences and three-dimensional sampling scanning technologies, new technologies of magnetic resonance angiography and cinematography have entered the clinic and are becoming more and more perfect. The combination of magnetic resonance imaging and local spectroscopy (that is, the combination of MRI and MRS) and magnetic resonance imaging of atomic nuclei other than hydrogen protons such as fluorine, sodium, phosphorus, etc. have been achieved. These achievements will more effectively improve The specificity of resonance imaging diagnosis also broadens its clinical use.
The main disadvantage of magnetic resonance imaging is that it takes a long time to scan, so it is often difficult to check some uncooperative patients. It is often not clear about the lack of suitable contrast agents for sports organs, such as the gastrointestinal tract. ; For the lungs, imaging results are also unsatisfactory due to respiratory movements and low hydrogen proton density in the alveoli. Magnetic resonance imaging is not as accurate and sensitive as CT in the display of calcified lesions and bone lesions. The spatial resolution room of magnetic resonance imaging needs to be further improved.
1. MRI of the craniocerebral and spinal cord is more sensitive than CT in the diagnosis of brain tumors, encephalitis, white matter lesions, cerebral infarction, and congenital abnormalities of the brain. The lesions at the base of the skull and brainstem can be more clearly shown without artifacts. MRI can show cerebral blood vessels without contrast agents, and find the presence of aneurysms and arteriovenous malformations. MRI can also directly display some cranial nerves, and early lesions that occur on these nerves can be found. MRI can directly display the whole picture of the spinal cord, so it has important diagnostic value for spinal cord tumors or spinal canal tumors, spinal white matter lesions, spinal cavities, and spinal cord injuries. For disc disease, MRI can show degeneration, protrusion or bulging. The spinal stenosis was also better. For the cervical and thoracic spine, CT often shows dissatisfaction, while MRI shows clearly. In addition, MRI is also very sensitive to showing metastatic tumors of the vertebral body.
2. The head and neck MRI shows good tumorous lesions in the eyes, ear, nose, throat, and throat. For example, nasopharyngeal carcinoma invades the skull base and cranial nerves. MRI can also do angiography of the neck, showing abnormal blood vessels. For neck masses, MRI can also show its range and characteristics to help characterize it.
3. Chest MRI can directly display the myocardium and left and right ventricular cavities (controlled by ECG gating), can understand the situation of myocardial damage and can measure heart function. The condition of the large vessels in the mediastinum can be clearly displayed. It is also very helpful for qualitative localization of mediastinal tumors. Can also show the situation of pulmonary edema, pulmonary embolism, lung tumors. Can distinguish the nature of pleural effusion, distinguish between vascular section or lymph node.
4. Abdominal MRI can provide very valuable information for the diagnosis of liver, kidney, pancreas, spleen, adrenal gland and other solid organ diseases, which is helpful to confirm the diagnosis. It is also easier to show small lesions, so early lesions can be found. MR pancreaticobiliary angiography (MRCP) can show bile ducts and pancreatic ducts, and can replace ERCP. MR urography (MRU) can show dilated ureters and renal pelvis and calyces, and is especially suitable for patients with poor renal function and undeveloped IVU.
5. Pelvic MRI can show pathological changes of uterus, ovary, bladder, prostate, seminal vesicle and other organs. You can directly see the endometrium and muscle layer, which is very helpful for the early diagnosis of uterine tumorous lesions. It is also of great value for the qualitative diagnosis of ovarian, bladder, and prostate lesions.
6. Retroperitoneal MRI is of great value for showing tumors in the retroperitoneum and its relationship with surrounding organs. Can also show abdominal aorta or other large blood vessel lesions, such as abdominal aortic aneurysm, Budd-Jackson syndrome, renal artery stenosis and so on.
7, musculoskeletal system MRI damage to the cartilage discs, tendons, ligaments in the joints, the display rate is higher than CT. Because it is more sensitive to changes in bone marrow, bone metastases, osteomyelitis, aseptic necrosis, and bone marrow infiltration in leukemia can be detected early. The soft tissue mass of bone tumors is clearly displayed. It also has certain diagnostic value for soft tissue injury.
- The amount of information provided by MRI is not only greater than
- 1. Nervous system diseases:
- Sweep
- Scanning without contrast injection
- Enhanced MRI scan
- A type of diagnostic agent that reduces the resonance time of tissues under the action of external magnetic fields, increases the difference in contrast signals, and improves the contrast and sharpness of imaging by injecting MRI contrast agents. It is an inspection method that can effectively change the local water proton relaxation rate in biological tissues, shorten the relaxation time of protons in water molecules, and accurately detect the difference between normal tissues and diseased parts.
- SE spin echo sequence
- The order of applying pulses in MRI is to first give a 90 ° excitation pulse, and then give a 180 ° phase refocusing pulse, so there is only one 180 ° pulse in a TR, which is called a spin-echosequence (SE) .
- FSE / TSE fast spin echo sequence
- The FSE sequence is a sequence based on the SE sequence. The order of applying pulses in MRI is to first give 90 ° excitation pulses, and then give multiple 180 ° phase refocusing pulses in the same direction to form an echo chain (ETL). Therefore, the scanning time is shortened, which is referred to as a spin-echo sequence (FSE).
- IR fast reverse sequence
- By transmitting 180 ° reverse pulses, some protons in the tissue reach saturation first, and then 90 ° -180 ° -180 ° one pulse is emitted. Since the protons that have reached saturation do not generate a signal, the suppression effect is achieved. Suppression) and FLAIR (Free Water Suppression).
- GE / GRE gradient echo sequence
- in
- According to the magnetic composition, MRI contrast agents can be divided into three categories: paramagnetic, ferromagnetic and superparamagnetic. The tritium contrast agents commonly used in clinical practice are paramagnetic contrast agents.
- At present, there are six small-molecule europium complex contrast agents used in clinical practice, respectively: (NMG) 2 [Gd (DTPA) H2O)] (Magnevist), Gd (DTPA-BMA) (Omniscan), (NMG) [Gd (DOTA) (H2O)] (Dotarem), Gd (HP-DO3A) (Prohance), (NMG) 2 [Gd (BOPTA) (H2O)] (MultiHance), Gd (DO3A-butrol) (H2O) ( Gadovist)