From 30 million to 2.6 million, what benefits can domestically produced MRI machines bring to the people?

Audit expert: Meng Meng

Associate Researcher, Institute of Physics, Chinese Academy of Sciences

A while ago, everyone's mobile phone may have been flooded with a piece of news: China's domestic MRI machines have entered mass production. According to relevant news reports, the price of related equipment has dropped from more than 30 million to less than 3 million, a drop of more than 90%.

Since the beginning of the 21st century, continuous breakthroughs have been made in magnetic field strength, magnet linear indicators, etc., making nuclear magnetic resonance technology no longer limited to laboratories, but gradually moving into the medical field and becoming an important modern medical testing method.

Everyone has heard of nuclear magnetic resonance, and many people have experienced it when they went for a checkup, but what is the principle behind nuclear magnetic resonance? What benefits will it bring to us if nuclear magnetic resonance instruments are made domestically?

Image source: CCTV News

1

What is NMR?

In order to study the atomic structure and physical properties of substances, people construct a strong external magnetic field to orient most atoms and apply electromagnetic pulses of different wavelengths to make them present different information in the spectrum . This spectroscopy method is Nuclear Magnetic Resonance Spectroscopy (NMR). This method receives information at the atomic level, so it can qualitatively analyze the elemental composition and structure of different substances.

Source | "Nuclear Magnetic Resonance Spectrum Analysis"

Nuclear magnetic resonance technology has been widely used in many fields. In the chemical industry , nuclear magnetic resonance technology can accurately detect whether the fuel loaded in the rocket engine is defective and clearly understand the distribution of different substances; in the field of geological exploration , nuclear magnetic resonance technology can understand the geological information or resource distribution in the mining area in a short time with almost no impact. The application of nuclear magnetic resonance technology has significantly improved the efficiency of resource exploration, reduced the accident rate, reduced costs, and made many industries more modern and information-based. In the medical field , we usually come into contact with nuclear magnetic resonance imaging (MRI).

2

What is the principle of medical MRI?

The development of physics is, to some extent, a process of continuous subdivision of matter. Classical physicists believe that the smallest unit of matter is the atom. Going deeper on the basis of the atom, scientists discovered that it can be divided into even smaller particles, namely protons, neutrons and electrons.

In terms of particle composition, neutrons are uncharged, the nucleus is positively charged, and the electrons are negatively charged. Electrons are attracted by protons in the nucleus, and the positive and negative charges of the two cancel each other out. The number of neutrons may be zero, so the atom as a whole is electrically neutral. Protons and neutrons form the nucleus in the center of the atom, and electrons move around the nucleus on the outside.

In addition, we all know that the water content in our body can reach 70%. Generally, we use H2O to represent a water molecule, which contains only one oxygen atom and two hydrogen atoms, and its shape is similar to the head of the cartoon character Mickey Mouse.

Image source | Baidu Encyclopedia

The nucleus of a hydrogen atom is composed of only one proton. If a proton is regarded as a sphere, then like a celestial body, it will also rotate about a straight line passing through the center of the sphere. Protons are charged, and the movement of charged particles will generate a magnetic field, which forms a nuclear magnet formed by the rotation of the nucleus.

Source | Introduction to Nuclear Magnetic Resonance Instrument

When a person lies in a nuclear magnetic device, a magnetic field tens of thousands times larger than the Earth's magnetic field is created by the device and passes through the human body, causing more than half of the atoms to be arranged in a specific direction. The remaining atoms that are not so "well behaved" will precess around that direction (similar to the left-right swing of a rotating bicycle wheel).

Studies have shown that the frequency of this precession is proportional to the size of the external magnetic field. Therefore, if an instrument is used to apply a magnetic field that changes linearly from head to toe, the precession frequency of each axial position of the human body will also change linearly .

In this way, the human body is like a pipa, and the electromagnetic pulses of different wavelengths emitted by the instrument are the fingers plucking the strings. The strings are deformed by the pressure of the fingers, and emit "sounds" when the fingers are released. These "sounds" can be analyzed by professional equipment to obtain a lot of information about the human body.

3

How domestic nuclear magnetic resonance instruments rose to prominence

As mentioned above, in order to make the atoms in the human body "obedient", equipment is needed to build a strong magnetic field, which requires extremely large electric current.

According to Joule's law, the heat generated by a conductor is proportional to its resistance and the current passing through it. In order to control the heat generated when the current is particularly large, the resistance of the conductor must be reduced, which is not an easy task. Therefore, the commonly used method now is to place the conductor in an environment with an extremely low temperature (below -260°C) . Perhaps everyone has paid attention to the news about room temperature superconductivity. It is conceivable that if this technology is broken through, it will cause a great shock to the industry.

At the same time, the continuous and stable existence of the equipment in a low-temperature environment requires a strong power supply, advanced technology and a complete industrial production line. In addition, some special parts also have high technical requirements, such as nuclear magnetic signal image conversion devices, control chips, radio frequency signal receiving and transmitting devices, etc. Due to poor foundations and late start, the Chinese nuclear magnetic equipment market has been monopolized by some foreign companies for a long time. Whether it is purchasing or maintaining related equipment, we have to pay a high price.

Now, China's independently developed nuclear magnetic resonance equipment has been put into use. According to doctors at Peking University Shenzhen Hospital, compared with foreign instruments used in the past, China's independently developed instruments have the advantages of high resolution and fast imaging speed. The most important thing is that the maintenance cost is low and the operation is simple, which greatly reduces the cost . I believe that it will definitely benefit the majority of patients in the future.

Source | CCTV News

The rise of domestic nuclear magnetic resonance instruments is closely related to the innovation of my country's scientific research mechanism. Researchers at the Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences said that as early as the beginning of the project, the research team had close communication with the industry, and the matching degree of industrial needs was set as one of the most important indicators for testing scientific research results. With the long-term development of Chinese science as a foundation, coupled with the unremitting efforts of the research team and the industry, we can achieve comprehensive breakthroughs in many fields including nuclear magnetic resonance.