Do you know MRI?
Magnetic resonance imaging (MRI), also known as spin imaging, uses the principle of nuclear magnetic resonance (NMR) to detect the emitted electromagnetic waves by applying a gradient magnetic field based on the different attenuation of the released energy in different structural environments within the substance. The position and type of the nucleus of the object can be known, and the structure image of the object can be drawn based on this.
Principle overview:
MRI is a biomagnetic nuclear spin imaging technology that has developed rapidly with the development of electronic computers, electronics, circuits, superconductors and other technologies. Doctors take into account the patient's fear of "nuclear", so this technique is often called "magnetic resonance imaging."
The "nucleus" of MRI refers to hydrogen nuclei, because about 70% of the human body is composed of water, and MRI relies on hydrogen atoms in water.
When an object is placed in a magnetic field, it is irradiated with appropriate electromagnetic waves to change the direction of the hydrogen atom's rotational arrangement to make it resonate, and then analyze the electromagnetic waves it releases. Different tissues will produce different electromagnetic wave signals, which are processed by the computer. You can know the position and type of the nuclei that make up this object, and based on this, you can draw an accurate three-dimensional image of the inside of the object.
During the precession of the atomic nucleus, it absorbs the radio frequency pulse with the same frequency as the precession frequency of the atomic nucleus, that is, the frequency of the applied alternating magnetic field is equal to the Larmor frequency, and the atomic nucleus undergoes resonance absorption. After the radio frequency pulse is removed, the nuclear magnetic moment reduces the absorbed energy Part of it is emitted in the form of electromagnetic waves, which is called resonance emission. The process of resonance absorption and resonance emission is called "nuclear magnetic resonance".
Disadvantages of MRI:
The lung examination is not superior to X-ray or CT examination, and the liver, pancreas, adrenal gland, and prostate examination is not superior to CT, but the cost is much higher;
It is not as good as endoscopy for gastrointestinal diseases;
The scanning time is long and the spatial resolution is not ideal;
Due to the strong magnetic field, MRI cannot be applied to special patients with magnetic metal or pacemakers in the body.
