What is the working principle of magnetic resonance imaging (MRI)

Magnetic resonance scanner (MRI) uses very strong magnetic fields and radio waves, which interact with protons in the tissue to generate a signal, which is then processed to form a human image. Protons (hydrogen atoms) can be considered tiny bar magnets with North and South poles, rotating around their axis - just like planets. Under normal circumstances, protons are randomly arranged, but when a strengthened magnetic field is applied, the direction of the proton magnetic field will align with this direction.

Exciting protons with radio wave pulses of the correct frequency causes them to resonate and disrupt the magnetic arrangement. The excited proton releases absorbed energy in the form of an RF signal, and the emitter is received by the receiving coil on the scanner. The radio frequency that causes proton resonance depends on the strength of the magnetic field. In an MRI scanner, gradient coils are used to change the magnetic field intensity of the entire body. This means that different parts of the body will resonate at different frequencies. Therefore, by applying different frequencies in sequence, you can image various parts of the body separately and gradually form an image.

Principles of Nuclear Magnetic Resonance Scanner

When the wireless power is turned off, the proton will return to its original undisturbed state (aligned with the magnetic field) and emit radio waves during this process, which are received by the receiving coil. Different tissues relax at different speeds, such as fat and water having different relaxation times, so relaxation time can reveal the type of tissue being imaged. There are two relaxation times that can be measured; T1- Time spent relaxing the magnetic line, T2- Time spent rotating back to a stationary state.

Multiple radio pulse sequences can be used to highlight or suppress certain tissue types. For example, there are usually no abnormalities inside fat, so fat suppression pulse sequences can be used to remove signals emitted by adipose tissue, leaving only signals from areas more likely to contain abnormalities.

MRI room 

Magnetic resonance imaging (MRI) scanners require a very strong magnetic field to drive; Usually around 1.5 Tesla, but it can also be 7 Tesla. In contrast, the Earth's magnetic field is only 0.00005 Tesla. A magnet is composed of multiple conductive wires, through which current flows to generate a magnetic field. In order to achieve the required high magnetic field strength, the magnet is cooled to below 10k (-442/-263oC) using liquid helium. This makes superconductivity possible, allowing current to flow in the coil without generating resistance, which means that when the magnet is overcooled, it can conduct greater current and thus generate stronger magnetic fields.

In 1971, Paul C. Lauterbur of the University of Illinois in the United States invented magnetic resonance imaging technology. This technology was subsequently developed by Sir Peter Mansfield and the first MRI scan of the human body was performed in 1977. Although it was not until the 1980s that the first MRI scanner capable of producing clinically useful images was introduced. This machine was designed by John Mallard, who is considered a widely used pusher for magnetic resonance imaging (MRI) and is used to identify and torture a patient