Definitions and differentiation of T1 and T2 in MRI [conversion]

Source: Internet
Author: User
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A. MRI terms refer to T1 weighted imaging and T2 weighted imaging, which are often referred to in the report of MRI. Many non-professionals do not understand what they mean. To understand what T1 weighted imaging and T2 weighted imaging mean, please first understand several basic concepts: 1. Magnetic Resonance (mageticresonancemr); the electromagnetic energy absorption and release of the nucleus in a constant magnetic field after the corresponding RF Pulse is stimulated, called magnetic resonance. 2. tr (repetitiontime), also known as the repetition time. MRI signal is very weak. To improve the signal-to-noise ratio of Mr, the same pulse sequence must be used repeatedly. The interval of this repeated excitation is called tr. 3. Te (echedelaytime): it is also called the echo time, that is, the time between the RF pulse radiation and the collected echo signal. 4. sequence: refers to the pulse Program-combination used in the check. Commonly used spin echo (SE), fast spin echo (FSE), gradient echo (GE), reverse recovery sequence IR), and plane echo sequence (EP ). 5. weightimage. Wi: Adjust the repetition time tr to judge the parameters of the detected tissue. The echo time te can be used to obtain an image that highlights a certain organizational feature parameter. This image is called a weighted image. 6. flowingvoid effect: because of the rapid flow of blood in the cardiovascular, the hydrogen proton emitted from the MR signal is removed from the acceptance range, but the MR signal is not measured. 7. Mr vascular imaging: There are two vascular imaging modes: Time overflight, time offlight, and TOF; and phase contrast, phase contrast, or PC. The former is imaged by longitudinal vector changes between the proton group and the static tissue of the blood flow, and the latter distinguishes the surrounding static tissue through phase contrast changes, highlighting the reconstruction of vascular images. Currently, the top method is widely used in clinical applications. 8. Mr water imaging: Based on TW2 images, it can inhibit other tissues and only show static water. This technique can be used for ventricular imaging, biliary imaging, and urinary tract imaging. 9. Relaxation: Under the excitation of RF pulse, the absorption energy of hydrogen proton in the human body is in the excitation state. After the RF Pulse is terminated, the hydrogen proton in the excitation state restores to its original state. This process is called relaxation. After understanding the above concepts, the magnetic resonance imaging process is described as follows: the nucleus (containing base proton or neutron, generally hydrogen proton) in the human body is magnetized in a strong magnetic field, after the gradient field is given Spatial positioning, the RF Pulse inspires the hydrogen proton at a specific inactive frequency to generate resonance, and the energy is released during the excitation of the hydrogen proton relaxation process, that is, the magnetic resonance signal, the computer collects Mr signals, converts them to black and white gray scales by intensity, and forms two or three dimensions by position to form MR images. In short, magnetic resonance imaging is an imaging technique that uses signals produced by resonance of the nucleus in the magnetic field for re-imaging. B. After explaining the above basic concepts, t1 and t2 can further understand what T1 and T2 weighted imaging means. The so-called weighted is the meaning of "prominent" T1 weighted imaging (T1)-highlight tissue T1 relaxation (longitudinal relaxation) Difference T2 weighted imaging (T2) ---- highlight the differences between the T2 relaxation (Transverse Relaxation) of the tissue. In any serial image, the larger the horizontal magnetization vector at the time of signal collection, the stronger the MR signal. T1 weighted image short TR, short TE--T1 weighted image, T1 image features: the shorter the Organization T1, the faster the recovery, the stronger the signal; the longer the Organization T1, the slower the recovery, the weaker the signal. T2 weighted image long TR, long TE--T2 weighted image, T2 image features: the longer the T2 tissue, the slower the recovery, the stronger the signal; the shorter the T2 tissue, the faster the recovery, the weaker the signal. Proton density weighted images: long TR and short te-proton density weighted images. image features: the larger the Rh of the tissue, the stronger the signal. The smaller the RH, the weaker the signal. The high signal generation mechanism of T1 weighted images is generally considered that the high signal on T1 weighted images is mostly caused by bleeding or fat tissue. However, recent studies have shown that T1-weighted high signal is still common in many types of intracranial lesions, including tumors, cerebrovascular diseases, metabolic diseases, and some normal physiological conditions. Under the excitation of RF pulse, the absorption energy of hydrogen proton in human tissue is in the excitation state. In the relaxation process, the hydrogen proton releases the energy it absorbs to the surrounding environment. If the proton and the proton in the lattice are also inactive at a frequency similar to the larmor frequency, then the energy of the hydrogen proton is quickly released, and the longer the T1 Relaxation Time of the tissue is, the higher the signal strength of the T1 weighted image. There are three kinds of T1 relaxation time shortening: first, water binding effect; second, maleic acid, and third, lipid molecules. C. differentiate t1 and t2 Method 1: 1. compared with the Mr films of the SE sequence, the short (<500 ms) (<25 ms) and short (> 2000 ms) of TR tet1wi can be determined based on the relationship between Tr, TE and weighted image) longer (> 75 ms) PDWI longer (> 2000 ms) shorter (<25 ms) 2. compared to the GRE gradient echo sequence (usually the gradient echo sequence is very small in TR and Te parameters), it is difficult to determine the film relying on parameters, which depends on indirect signs, for example, the signal level of the bladder, pelvis, ureter urine and cerebrospinal fluid containing a large amount of water is determined by the signal level, the water is bright to the t2nd, the water is dark to the low signal. 3. As for the pressure fat sequence, you can determine by the subcutaneous fat or peripheral fat signal. If it turns black, it indicates the pressure sequence. I hope these skills will help you !!!! Method 2: the liquid is bright on to t2nd, the liquid is dark to T1 from:

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