What is the principle of TE magnetic resonance physical imaging

Resonance imaging is an imaging technique that uses the resonance of atomic nuclei in a magnetic field to reconstruct the signal. Magnetic resonance imaging (MRI), as a new medical imaging diagnostic technology, has developed rapidly in recent years. MRI not only provides more information than many other imaging techniques, but also has great potential advantages for diagnosing diseases with its unique information.

Nuclear magnetic resonance (NMR) is a nuclear physical phenomenon. As early as 1946, Block and Purcell reported this phenomenon and applied it to spectroscopy. Lauterbur published the MR imaging technique in 1973, which made NMR not only useful in physics and chemistry.

It is also used in the field of clinical medicine. In recent years, magnetic resonance imaging technology has developed rapidly and has become more and more mature. The scope of the examination basically covers all systems of the whole body, and it is widely used around the world.

In order to accurately reflect its imaging basis and avoid confusion with nuclear imaging, it is now renamed magnetic resonance imaging. There are many factors involved in MRI imaging, which is informative and different from the existing imaging imaging, which has great advantages and application potential in the diagnosis of diseases.

What is the principle of NMR.

What is the principle of NMR.

Magnetic resonance imaging (MRI) is a new examination technology based on the principle that atomic nuclei with magnetic distance can produce transitions between energy levels under the action of magnetic fields. MRI is achieved by the action of high-frequency magnetic field in vitro, which is achieved by radiating energy from substances in the body to the surrounding environment, and the imaging process is similar to image reconstruction and CT, but MRI does not rely on external radiation, absorption and reflection, nor does it rely on the radiation of radioactive substances in the body, but uses the interaction between the external magnetic field and the object to image, and the high-energy magnetic field is harmless to the human body. So the MRI test is safe.

If the clinical classification of epilepsy syndrome is unclear, MRI can determine whether the patient is caused by changes in brain structure, intracranial tumors often cause epilepsy, and MRI has a very high diagnostic confirmation rate for low-grade astrocytoma, ganglion, glioma, arteriovenous malformation and hematoma in the brain. MRI can clearly show brain atrophy in patients with epilepsy, and the brain parenchyma and cerebrospinal fluid are excellent.

The main advantages of MRI compared to CT are:

Ionized radiation has no radioactive damage to brain tissue, nor does it cause biological damage.

Layered images of cross-sectional, sagittal planes, coronal planes and various inclined planes can be made directly.

There are no artifacts such as ray hardening that are found in CT images.

It is not disturbed by bone image, and can be satisfactorily displayed for small lesions in the posterior cranial fovea base and brainstem, and has high diagnostic value for tumors with cranial apex and parasagittal sinus, lateral fissure structures and extensive metastasis.

It shows that the pathological process of the disease is more extensive and the structure is clearer than that of CT. Isodense lesions showing complete normal CT can be found, especially demyelinating disease, encephalitis, infectious demyelination, ischemic lesions, and low-grade glioma.

MRI: Magnetic Resonance Imaging, English full name is: Magnetic Resonance Imaging

Principle. Nuclear magnetic resonance (NMR) is a physical phenomenon that was widely used as an analytical method in the fields of physics, chemistry and biology, and it was not until 1973 that it was used for medical clinical testing. To avoid confusion with radiological imaging in nuclear medicine, it is referred to as magnetic resonance imaging (MR).

MR is a kind of biomagnetic spin imaging technology, which uses the characteristics of the spin motion of the atomic nucleus, in the external magnetic field, after the radio frequency pulse excitation to generate a signal, detected by the detector and input into the computer, after computer processing and conversion, the image is displayed on the screen.

Principles of Imaging Description 1:

The principle of MRI: The nucleus of an atom is positively charged, and the 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 it is placed in an applied magnetic field, the spin space orientation of the nucleus transitions from disordered to ordered.

In this way, the core of the spin also rotates around the vector of the applied magnetic field at an angle between the spin axis and the vector direction of the applied magnetic field, which is called Lamor spin, like a spinning top rotating in the gravity of the Earth. The magnetization vector of the spin system gradually increases from zero, and when the system reaches equilibrium, the magnetization reaches a stable value. If the nuclear spin system is subjected to external actions at this time, such as a certain frequency of radio frequency excitation nuclei, the resonance effect can be caused.

In this way, the spin nucleus also spirals in the RF direction, and this superimposed precession state is called nutation. After the radio frequency pulse stops, the atomic nucleus that has been intensified by the spin system can not maintain this state, and will return to the original arrangement state in the magnetic field, and at the same time release a weak energy to become a radio signal, which can detect many signals and make them spatially resolved, and obtain the distribution image of the atomic nucleus in motion. The process by which the nucleus returns from an intensified state to a state of equilibrium arrangement is called the relaxation process.

The time it takes is called the relaxation time. There are two types of relaxation time, namely t1 and t2, t1 is the spin-lattice or longitudinal relaxation time, and t2 is the spin-spin or transverse relaxation time.

Summarizing the principles of imaging:

The nuclei of the elements undergo spin motion and are irregular;

With the addition of a magnetic field, the nuclear spin changes from disorder to order, and Lamor spins in; The system reaches equilibrium;

A certain frequency of radio frequency excites the nucleus, resonance effect, radio frequency direction precession, nutation;

The radio frequency pulse stops, the nucleus returns to its original arrangement in the magnetic field, releases weak energy, radio signals, detects these signals, and spatially resolves to obtain a picture of the distribution of the nuclei in motion.