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The Amazing Physics of Magnetic Resonance Imaging (MRI)

Apr 29, 2021 | Articles, MRI

One of the most amazing medical breakthroughs in the medical industry is magnetic resonance imaging or MRI. Various medical conditions can only be diagnosed using this technology. With a technological innovation such as the MRI, it is always interesting to know what makes it work and the elements that make it outstanding.

In this article, we’ll delve deeper into the physics of MRI.


MRI: The Science Behind It

MRI is composed of fundamental physical and technological aspects. This medical imaging technology is utilized mostly in nuclear medicine and radiology to detect any disorders such as tumors, blood vessel issues, and abnormalities in other parts of the body. 

Images are shown by the machine so that physicians will have a better look at the condition. MRI is safer than X-rays and CT scans because it does not use ionizing radiation. Children and adult patients who are required to have repetitive tests can undergo MRI without worry. 

Contrast agents can be injected into the joints or veins to acquire a more enhanced image of the affected body part. Patients with a cardiac pacemaker and other implants in their body can also safely undergo MRI.


So, how does this actually work?

You might be thinking about how an image can be generated with MRI technology. When certain atomic nuclei are placed in an external magnetic field, they will absorb and emit radiofrequency energy. 

Clinical studies found out that hydrogen atoms are most often used to produce a radio-frequency signal detected and received by nearby antennas. Hydrogen atoms are usually present in humans and other biological organisms, where there is a rich supply of fat and water. 

This explains why MRI can provide images from the inside of the body. The technology particularly maps the presence of water and fat in the specific area. Various contrasts are then generated when the pulses of radio waves are being stimulated by the nuclear spin transition and magnetic field gradients.

Protons can be either parallel or antiparallel aligned to magnetic fields’ direction when inside the scanner. Each proton usually has two types of alignments only. However, when there is a collection of protons, other alignments can be observed. Most of the protons are seen to align to B0 since this is in a lower state of energy.

When an amount of radiofrequency pulse is applied, this excites the protons and then forms a parallel to antiparallel alignment. As a result of the force applied to bring the protons back in their equilibrium state, they will undergo precession, a process somewhat like a rotating wheel due to the gravity’s effect. 

A changing voltage is received in coils wherein signals are given. The strength of the local magnetic field surrounding the protons dictates the frequency at which protons in a voxel will resonate. A stronger magnetic field correlates with a greater energy difference and a higher photon frequency. 

With the help of additional gradients placed over linear spaces, specific images can be selected. An image, then, is acquired by using the 2D images of the signal’s spatial frequencies. Patients usually hear knocking sounds due to the gradient coils trying to move when the force and current flow into the coils. This is why physicians recommend the patients use hearing protection during an MRI process.



MRI is composed of complex yet amazing physics. Its components and aspects do a good role in producing images of underlying health conditions. Every medical establishment should recognize the significance of a quality MRI machine to provide accurate diagnoses to their patients.

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