MRI, magnetic resonance imaging Automatic translate

Magnetic resonance imaging is a medical imaging technique that has revolutionized the field of diagnostics. Its invention, development and subsequent impact on healthcare are a testament to the relentless pursuit of scientific understanding and technological innovation. Modern models of tomographs in large clinics, such as CMRT (there are branches in several large cities of Russia), help patients accurately diagnose, and in many cases, avoid serious disorders in the body.

Story

The origins of the technique go back to the beginning of the 20th century, when scientists began to study the fundamental principles of nuclear magnetic resonance. In 1946, Felix Bloch and Edward Purcell independently discovered the phenomenon of nuclear magnetic resonance (NMR). Their pioneering work earned them the Nobel Prize in Physics in 1952. NMR laid the foundation for what would become MRI because it discovered the ability of tissues and environments to interact with the magnetic properties of atomic nuclei.

However, it was not until the 1970s that physician and scientist Raymond Damadian developed the first working MRI machine. His invention was aimed primarily at identifying pathologies in human tissue by measuring the relaxation time of hydrogen nuclei. The prototype of the device, known as Indomitable, became an important milestone in the history of medical technology, demonstrating its capabilities in the field of medical imaging.

Comparative analysis

MRI, CT, and radiography are three different imaging modalities, each with their own advantages and limitations. Let’s look at the main differences between MRI and other methods.

❶ Soft tissue contrast and resolution

MRI is excellent at visualizing soft tissue, making it the preferred choice for imaging the brain and spinal cord, assessing joint health, and detecting cancer. CT and radiography are better at visualizing bone and denser tissue, but have difficulty differentiating soft tissue.

❷ Radiation exposure

Unlike radiography and CT, MRI does not use ionizing radiation. This is a significant advantage as it eliminates the potential risks associated with radiation exposure, especially in children and pregnant women.

❸ Multiplanar imaging

MRI produces images in volume, which gives doctors the opportunity to view anatomical structures from different angles, which facilitates accurate diagnosis and planning of surgical interventions. CT and radiography, on the other hand, are more limited in this regard.

❹ Functional imaging

What makes MRI unique is its ability to perform functional imaging, such as functional MRI (fMRI), which can image brain activity, or diffusion-weighted imaging (DWI), which can evaluate tissue microstructure. These capabilities are not available with radiography and are limited with CT.

❺ Safety and contrast agents

MRI is considered a safer procedure for patients allergic to CT and X-ray contrast agents because it typically uses gadolinium-based contrast agents, which have a lower risk of allergic reactions.

Principle of operation

MRI is based on the principles of NMR and uses the magnetic properties of atomic nuclei, primarily hydrogen, which is present in abundance in the human body due to the presence of water molecules. The process begins by exposing the patient to a powerful magnetic field. This field aligns the hydrogen nuclei in the body along its direction. Radiofrequency pulses are then applied that briefly disrupt this alignment. After turning off the magnetic field, the hydrogen nuclei return to their original state, emitting radio frequency signals. These signals are picked up by special antennas and converted into detailed images.

A key advantage of MRI is its ability to provide unmatched soft tissue contrast. Unlike X-rays, which are absorbed primarily by dense materials such as bone, MRI can distinguish between different soft tissues, making it invaluable for diagnosing diseases of the brain, spinal cord, internal organs, and musculoskeletal system. In addition, unlike X-rays and CT scans, MRI does not involve ionizing radiation, which ensures patient safety in the long term.

How does a magnetic resonance imaging scanner work?

Magnetic resonance imaging works on the principles of nuclear magnetic resonance (NMR) and allows you to create detailed images of the internal organs of a person. Below is a step-by-step explanation of how the MRI machine works:

1. Magnetic field generation

The process begins with the generation of a powerful and uniform magnetic field inside the MRI machine. This magnetic field is created by a superconducting magnet, which is usually a large cylindrical magnet with a hole through which the patient can pass. Magnetic field strength is usually measured in units of Tesla (T) and can range from 1.5 T to 7 T and even higher in research facilities. The stronger the magnetic field, the higher the image resolution.

2. Alignment of hydrogen nuclei

The human body consists of a large amount of water, which contains hydrogen nuclei (protons). When a patient is placed in an MRI machine, the magnetic field aligns the hydrogen nuclei inside the body along its direction. This alignment is critical for subsequent steps.

3. Excitation by radio frequency (RF) pulses

An MRI machine uses radiofrequency pulses to produce images. These pulses are emitted by a coil that surrounds the body part being imaged. When a radio frequency pulse is applied, it temporarily disturbs the alignment of the hydrogen nuclei, causing them to change their magnetic moments.

4. Relaxation and signal emission

After the radio pulse is turned off, the hydrogen nuclei begin to relax, returning to their original position relative to the magnetic field. During the relaxation process, they emit radio frequency signals. The relaxation rate of hydrogen nuclei is characterized by two time constants: T1 (longitudinal relaxation) and T2 (transverse relaxation). Different tissue relaxation times in the body contribute to image contrast in MRI.

5. Signal detection

To record emitted radio frequency signals, the MRI machine uses specialized radio frequency coils. These coils act as antennas and pick up signals generated by relaxing hydrogen nuclei.

6. Signal processing

The detected signals are sent to a computer, which processes the received data. Complex algorithms and mathematical transformations are used to convert signals into meaningful images. These algorithms take into account variations in the relaxation time and spatial position of hydrogen nuclei.

7. Image reconstruction

Based on the processed data, detailed images of the cross section of the body are constructed. These images can be presented in different planes, such as axial, sagittal and coronal, allowing a complete picture of the internal structures. The contrast and detail of images depend on the properties of tissues and relaxation time.

8. Additional imaging methods

In addition to basic anatomical imaging, MRI can use a variety of techniques to obtain functional and physiological information. Functional MRI (fMRI) allows you to map brain activity, diffusion-weighted imaging allows you to evaluate tissue microstructure, magnetic resonance angiography (MRA) allows you to visualize blood vessels, etc.

9. Image interpretation

The resulting MRI images are interpreted by radiologists and medical professionals to diagnose and monitor a wide range of diseases, including brain diseases, musculoskeletal injuries, tumors, and others. The exceptional contrast of soft tissue makes MRI a valuable tool in clinical practice.

MRI’s ability to produce high-quality, non-invasive images with excellent soft tissue contrast has made it an invaluable tool in modern medicine for diagnosis, treatment planning and medical research.