Why is an MRI scan not harmful? Or is it harmful?

Today we will talk about the most common misconception related to MRI:

«You can’t have an MRI often, you’ll get a high dose of radiation and cancer

Let’s figure out if having an MRI is harmful?

Magnetic Resonance Imaging (MRI) is a method of radiological diagnostics,   as well as computed tomography (CT). Both methods allow obtaining images of internal organs and soft tissues for the purpose of diagnosing diseases or injuries. However, the physical mechanisms for obtaining these images are completely different!

In this article, we discuss CT and MRI without contrast. The safety of contrast is a separate topic.

Let’s compare the physics of X-ray and MRI

X-ray

During a radiological examination (which is a CT scan), X-ray radiation is used – electromagnetic radiation with a high frequency (3⋅10¹⁶ Hz — 6⋅10¹⁹ Hz). Let’s simplify the explanation as much as possible, although everything in the body is much more complex.

• Penetrating the human body, part of the radiation is absorbed. It’s similar to projecting a film in a cinema. We see on the image the places where the X-ray passed through and where it was absorbed.
• When absorbed by tissues, X-ray radiation causes ionization, which is why the radiation is called ionizing.
• Ionization chemically activates atoms, such as oxygen.
• Ionization of oxygen atoms leads to activated oxygen atoms eagerly combining with molecules in the cell, including, for example, with DNA.
• DNA altered by attached oxygen is copied incorrectly. All its copies become altered. This is called a mutation.
• Reading altered (mutated) DNA provides incorrect information. It is similar to a choir of body cells starting to sing off-key.
• Incorrect information causes incorrect processes in the body. The degree of disorders depends on the mutation, just as music depends on a mistake in the notes. Sometimes the mistake destroys the entire harmony, sometimes we may not catch it, and sometimes, very rarely, it can make “музыку ” even better

CT scans can cause changes in DNA molecules, which can lead to two types of consequences: direct and stochastic.

• With direct exposure, a certain dose will always cause specific damage. Cells that divide frequently will suffer significant DNA damage. They will begin to die en masse. For example, someone who receives a lethal dose at once will experience life-incompatible damage. Direct damage is caused by doses much larger than those in CT. Even doctors working daily in interventional radiology and operating under X-ray do not receive such doses.
• But in everyday life, we experience stochastic effects. These are probabilistic events—receiving such a dose does not necessarily lead to specific damage. It is incorrect to talk about stochastic effects: “such a dose – cancer will definitely appear “, correct to say so: “the more you gain, the higher the probability “. It might be lucky if the body copes, or it might not be. It’s similar to a situation where you slightly ruin “Notes “, that the choir sings. A good musician can still sing correctly because they know the music even without the notes, and they can also correct these notes. This happens in the body. Radiation can lead to cancer or premature aging, or it may not.

Unlike CT, MRI machines do not use ionizing radiation. A recent research article in 2024 states that field strength below 2.0 Tesla does not have a significant biological impact on humans.

MRI tomography

Did you know that initially, MRI was called nuclear magnetic resonance imaging (NMR)? This is because the method is based on the resonance of the magnetic field of small (at the quantum level) magnets in atomic nuclei – protons. The word “Nuclear was removed from the name, partly because nuclear reactions, which cause dangerous radiation, have nothing to do with MRI, and people are very afraid of this word, especially after Chernobyl.

So how is an MRI image obtained?

Let’s simplify again. In MRI diagnostics, data is obtained through a magnetic field and the mechanism is not absorption, but echo!

• In hydrogen protons, the positive charge does not have a specific location; it flies around randomly like a fly in a jar. But our fly is magical—it is charged. A moving charge creates an electromagnetic field and interacts with it
• When we apply a constant magnetic field, imagine a fly being attracted to the edge of a jar but continuing to fly. The stronger we attract, the more it vibrates, because there is less and less space for flying.
• Now let’s move on to another analogy: different frequency resonance for producing the sound of a guitar string depends on the tension of the strings. Similarly, the frequency of an imaginary fly in a jar depends on the strength of the magnetic field.
• Do you remember when you make a sound, the resonance of the guitar strings makes them sing back to us? The same is true with our hypothetical fly, when we apply a variable electromagnetic field of a certain frequency. Our “fly ” sings in response to a variable electromagnetic field, like a guitar hanging on the wall
• In MRI, time-varying aperiodic electromagnetic pulses (approximately in the range of 100–1000 Hz) and radiofrequency electromagnetic waves (in the range of 20–300 MHz) are used. These frequencies are billions of times lower than those of X-rays. In the case of MRI, the photon energy, which is proportional to frequency, is insufficient for ionization.
• The magnetic field closer to the center of the MRI machine is significantly stronger. Let’s place the jars with these magical flies at different distances from the center of the MRI. Closer to the center “flies ” будут “sing ” higher notes , further from the center lower .
• Now, we will start producing sounds of different pitches (frequencies) and listen to which flies respond to us. All the flies sang in response to each of their notes – this means there were flies in all the jars.
• If you remove a fly from one jar, you won’t hear its notes at its frequency, but the other flies will sing their notes.
• Now imagine these jars are points on your MRI scan. If we color the jars differently where the flies responded and did not respond.
• MRI can be tuned to the protons of hydrogen atoms and create a map showing where there is more water. “Watery ” areas will be whiter “Sukhikh “.

The essence of MRI is the echo of magnetized protons. The magnetic field used in MRI has a relatively low frequency. Just like the field used in a radio or television, it does not cause ionization and does not affect chemical reactions. Therefore, MRI is no more dangerous than a television broadcast flying through the air to a turned-off TV.

MRI is safe, but there are always nuances!

Despite the absence of physical and chemical prerequisites (ionization), there are several aspects that not everyone considers.

The impact of MRI on the fetus in the first trimester

There is a 2016 study involving one and a half million newborns, which indicates no effect of MRI in the first trimester of pregnancy). However, there is still no consensus that there is enough research, especially for the first trimester, so the decision is made individually based on risk and benefit.

MRI has contraindications and can be dangerous in some cases.

Article: When MRI Can Be Dangerous, for Example, MRI-Incompatible Metallic Foreign Bodies (MRI-incompatible clips, MRI-incompatible pacemakers, or shrapnel fragments). The danger is related to the impact of the magnetic field on these foreign bodies.

Magnetization

There is an exotic theory that microgranules of iron can become magnetized in brain cells. This hypothesis has not yet been confirmed by any real manifestations of this influence on health.

Noise-Induced Hearing Loss

There are publications suggesting that MRI noise can cause hearing loss. A case is described where a patient developed hearing loss and tinnitus after undergoing an MRI scan at 3 Tesla for the diagnosis of chronic back pain. Hearing tests revealed unilateral sensorineural hearing loss, which resolved after 3 days, although tinnitus persisted. This is likely related to a temporary increase in hearing threshold due to noise exposure, although the possibility of sudden sensorineural hearing loss cannot be ruled out.

Medicine stickers

Some patches contain foil, can heat up and burn.

Peripheral nerve stimulation during MRI

A changing magnetic field will generate current in a conductive medium and in the human body. Such currents can sometimes occur in nerve and muscle tissues, leading to a phenomenon known as peripheral nerve stimulation. Peripheral nerve stimulation can cause temporary sensations in the patient – tingling, twitching, or tapping, but current safety regulations limit the parameters of magnetic field changes to levels well below those required to cause pain or heart stimulation. We provide patients with a handheld emergency signal if they become uncomfortable during the scan.

The Human Factor as a Danger in the MRI Room

A properly conducted study, taking into account the indications and MRI contraindications, will be safe for you unless there’s human error from the staff! For example, someone might bring a heavy metal object into the MRI room in the hustle. There’s a tragic story where a six-year-old boy was killed by a magnetized oxygen tank in an MRI. If staff forget about this, inattention can end in tragedy. At our center, we have a special philosophy. We strive to eliminate the human factor as much as possible. Look at the photos below.

Objects near the MRI are secured with straps so that safety is ensured independently and does not rely on staff attention!

Nurse Yulia Mukhina secures the medical aspirator to prevent it from being brought into the MRI room at a dangerous distance if needed in an emergency situation

Conclusion

It is possible to perform an MRI without contrast multiple times if there are no contraindications, without fearing the development of oncology. The question about contrast is a separate issue because contrast is a foreign medicinal substance.

MRI is a compromise between quality and examination time. MRI examinations with us take longer. We do not believe in saving time at the expense of quality. We consider all, even non-obvious nuances, and our team provides you not just “MRI images “, and answers to questions and solutions to riddles!

Bless you!