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Earlier this year, a 40-year-old Brazilian man accompanied his mother to a doctor with a pistol at his waist and did not remove it after entering an MRI room.

There, a bullet from the pistol was fired and lodged in his abdomen. The injured man was rushed to hospital and died after two weeks of treatment.

The incident occurred at Laboratorio Cura in Sao Paulo, Brazil, and a statement issued by the medical facility said: "The patient and accompanying person were properly instructed about the procedure for entering the examination room and warned to remove all metal objects. Police also revealed that the man had signed an agreement stating that the terms of the MRI room had been confirmed.

But somehow he didn't leave his pistol outside the examination room, and that dangerous decision cost him his life.

People today are familiar with magnetic resonance imaging (MRI/NMRI) techniques, which are commonly used in hospital MRI examinations. Simply put, it relies on a powerful magnetic field to "see through" the internal conditions of the human body, allowing doctors to find hidden diseases in patients.

We have a lot of water in our bodies, and the most indispensable thing in water is hydrogen atoms. Each hydrogen nucleus (i.e., proton) is like a tiny magnet that possesses an intrinsic property called spin, which in turn generates a magnetic field. Under natural conditions, hydrogen nuclei have their own spin directions, and the magnetic fields generated are chaotic and cancel each other out.

But when the machine applies a strong magnetic field from the outside, the spin directions of the hydrogen nuclei become regular: some become aligned with the main magnetic field and have lower energies, while others are opposite to the main magnetic field and have higher energies. The point was that the former was slightly more numerous than the latter, so the magnetic field they produced would not be completely cancelled, and the extra part was the key to imaging.

When an external magnetic field is applied, the spin direction of the hydrogen nuclei changes (Credit: NIBIB gov via Youtube). On top of the main magnetic field, the instrument applies a radio frequency pulse, which causes the hydrogen nuclei to resonate magnetically. Some of the "excess" low-energy hydrogen nuclei absorb energy, jump to higher states, and change their spin direction. When the RF pulse disappears, the hydrogen nucleus releases energy and returns to a stable, low-energy state. Energy is emitted in the form of electromagnetic waves, and instruments collect such signals as the basis for imaging the body.

MRI relies mainly on signals released by hydrogen nuclei in water molecules to image, and the signals collected by the instrument vary according to the water content of different human tissues. In this way, the equipment can draw the appearance of various parts of the human body.

For MRI instruments, the stronger the main magnetic field it applies, the higher the signal-to-noise ratio and the better the image quality obtained. Medical MRI equipment applies magnetic fields that are often between 0.5 and 3 Tesla (tens of thousands of times the Earth's magnetic field) and sometimes higher. These strong magnetic fields can help doctors see abnormalities in patients, but they can also be dangerous. Ferromagnetic metallic objects (such as iron, cobalt, nickel) are easily absorbed by magnetic fields, and if these metallic objects are brought into the NMR chamber, the consequences may be very serious.

How bullets fire Scientists at the University of California, Berkeley, have tested some metal objects using an MRI machine (do not copy). For example, when a stapler is thrown into a working device, it jumps up and down rapidly in a strong magnetic field of 4 Tesla and eventually gets sucked to the inner wall.

Image source: practiCal fMRI via Youtube In addition to observing the force with which MRI machines drive metal objects with the naked eye, you can actually measure how much force that force is. For example, scientists feed a wrench into the instrument, which is connected to a scale at the other end. When the wrench swings violently up and down, the scale reads 280 pounds, equivalent to more than 1200 Newtons of tension-perhaps a hundred times the weight of the wrench itself.

The heavier a metal object, the more force it will experience in the same magnetic field. When scientists tested a swivel chair with an MRI machine, the scale initially read about 1300 pounds (~590 kilograms) when the chair got stuck in the "doorway" of the machine.

Image source: practiCal fMRI via Youtube But the magnetic field will not give up because of temporary jamming, still trying to suck the chair into the "belly", not hesitate to destroy the chair. When the back of the chair peeled off a layer of skin, the scale read about 1700 pounds (~770 kilograms). When the chair leg snapped, with a crisp sound, the hands eventually turned to nearly 2000 pounds (~900 kilograms)-almost the weight of a small car.

In 2016, in a hospital in Shanghai, family members of patients pushed wheelchairs into MRI rooms. At that time, the MRI machine was in standby mode, and the magnetic, metal wheelchair was immediately sucked in, causing damage to the machine. Fortunately, no one was injured.

Handguns may not seem like a regular hospital item compared to wheelchairs, but it's not the first time such weapons have caused accidents in an MRI room.

A 2002 study published in the American Journal of Roentgenology documented a case in which an off-duty police officer went to a medical imaging center for an MRI and, due to some misunderstanding in doctor-patient communication, brought a pistol into the MRI room. The officer tried to put the gun on the cabinet (less than a meter away from the MRI equipment), but halfway through the action, the gun flew out of his hand, was sucked into the MRI equipment, slammed into the inner wall, and fired a bullet. At this moment, the trigger was not pulled.

Under normal circumstances, after the trigger is pulled, the sear that originally blocked the hammer (hear) will move away, and when the hammer is released, it will move forward and hit the firing pin, which will then hit the primer and ignite the powder. Eventually, the high-pressure gases created by the burning powder will launch the bullet.

The firing pin block, as indicated by the arrow (image source: original paper), and one condition for the firing pin to hit the primer is that the firing pin block is removed. It's a metal stop that's supposed to be held up by a small spring that gives way when the trigger is pulled. Scientists believe that this spring does not exert much pressure on the stylus stop. In addition to pulling the trigger, the magnetic field can also overcome the force of the spring and move the stylus stop away.

Of course, it is not enough to remove the striker block. Without pulling the trigger, another force is needed to make the firing pin hit the primer. The researchers found white marks on the muzzle, which means the muzzle may have hit the MRI device at the time of the accident. They believed that the muzzle was now subjected to enough force to drive the hammer toward the primer and ignite the powder.

If this is the case, the hammer is skipped to the hammer pin, and it doesn't matter whether the iron blocks the hammer or not. This meant that bullets could be fired regardless of whether the manual safety of the bolt was activated (the safety only ensured that the stop iron would not give way). Scientists say this may be why the gun was still firing when the safety was off.

Fortunately, that bullet only hit the wall and did not hurt anyone. This year, however, the Brazilian man who accompanied his mother to see a doctor paid with his life.

Where's the dangerous metal? Maybe the pistol's a long way from your life and mine. Other metal objects, which may be closer to us, also carry a fatal risk if they are taken into the MRI room.

In 2018, a man in India brought a steel oxygen cylinder into an MRI room while visiting relatives in a hospital. As a result, he was pulled violently by a magnetic field to an MRI machine and died unfortunately. The investigation believes that his death may have been caused by inhalation of liquid oxygen leaking from an oxygen cylinder, which should have been damaged and leaked when it hit the machine. The victim's family said the oxygen bottle was requested by a worker who assured him the machine was turned off. The worker and another doctor were arrested.

In 2021, in an accident in South Korea, medical staff moved a 128-centimeter-high oxygen cylinder into an MRI room after an elderly patient was suspected to need oxygen. An oxygen cylinder 2 meters away from the MRI machine was sucked into the machine, causing intense pressure on the patient's head and chest, resulting in his death.

Photo source: Chao Xian Daily People take the initiative to bring metal objects into the MRI room, just one situation. In another case, the metal objects are inside people's bodies. For example, the metal parts of some pacemakers, especially early models, are affected by the strong magnetic fields of MRI machines, and more than one patient has died as a result. However, with the development of technology, more and more MRI-compatible cardiac pacemakers are available.

The magnetic field generated by MRI instruments can not only produce strong forces on ferromagnetic metals, but also make those metal materials heat up, both of which may cause harm to the human body. Over time, many implants, such as steel nails, artificial joints, heart stents, brain aneurysm clips, etc., are gradually abandoning ferromagnetic metals and turning to non-ferromagnetic metal materials.

However, it is not easy to judge whether the "parts" installed on yourself or your family can enter the MRI room if you are not a professional. Consulting a doctor may be our best option.

Original paper:

https://www.ajronline.org/doi/10.2214/ajr.178.5.1781092

References:

https://www.ncbi.nlm.nih.gov/books/NBK564320/

https://www.youtube.com/watch? v=1CGzk-nV06g

https://med.stanford.edu/bmrgroup/Research/mri-near-metal.html

https://www.scmp.com/week-asia/health-environment/article/3152827/man-dies-after-oxygen-cylinder-sucked-mri-machine

https://med.stanford.edu/bmrgroup/Research/mri-near-metal.html

This article comes from Weixin Official Accounts: Global Science (ID: huanqiukexue)

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