SINGAPORE - Magnetic resonance imaging, or MRI, is considered one of the safest ways to look deep inside the body, as it does not carry the radiation risk of X-rays or positron emission tomography scans.

Still, as MRI uses a powerful magnetic field to produce images, accidents can sometimes happen - such as in the case of an Indian man in Mumbai who died on Saturday (Jan 27).

Mr Rajesh Maru, 32, was holding a metal oxygen cylinder when he accompanied a relative into the MRI room.

The powerful pull of the MRI machine sucked Mr Maru in. According to reports, Mr Maru was trapped in the machine and inhaled liquid oxygen that leaked from the cylinder and died as a result.

MRI machines are well-suited to scanning non-bony parts of the body, such as the nervous system, muscles and tendons. Their intense magnetic field forces protons - tiny parts of atoms - in the body to align with the field. The machine then sends a radiofrequency pulse through the body, causing the protons to move.

Once the radiofrequency pulse ends, the protons realign with the field and release electromagnetic energy, and the MRI machine can detect the different types of tissue depending on how quickly the protons realign and how much energy they release.

During the process, the patient is placed inside the MRI machine and must stay very still to prevent the image from blurring.

What happened to Mr Maru is a rare accident, as those who wish to enter an MRI room are first made to remove all objects that can be magnetised from their bodies.

This is because anyone entering the room will be exposed to the strong magnetic field, which can turn these objects into dangerous projectiles that fly towards the machine.

For instance, in 2001, a six-year-old child undergoing an MRI scan in New York was killed when a metal oxygen tank in the same room flew towards the machine and smashed against his skull.

Even larger objects such as an office chair, for instance, can be sucked into an MRI machine with great force, as an online video below shows.

Dr David Hintenlang, from the Ohio State University Wexner Medical Centre, told The New York Times last year that some clothes such as socks and underwear contain metal in unexpected places - which is why patients are usually asked to change into hospital gowns before an MRI.

Patients with body piercing jewellery are also asked to remove them before an MRI scan.

In addition, patients are asked if they have implanted medical devices such as a cochlear implant or older pacemakers.

As the imaging system's magnetic field can slightly shift or heat up embedded metal and disrupt the activities of medical devices in the body, safety measures need to be taken.

In some cases, people with implants or embedded metal cannot safely get an MRI and must use a different scanning technology instead.

Sometimes, MRI scans can cause tattoos to burn the skin as the ink contains material that can be magnetised. All with tattoos should therefore be screened before a scan.

Transdermal patches used to deliver medicine through the skin may also contain aluminium foil or metallic parts that can heat and burn patients during an MRI. Patients whose patches have these components should remove them.

According to UC San Diego Health, a medical centre, an MRI will not normally affect dental fillings. However, the fillings may distort images if a scan of the neck, brain or facial area is being made. Similarly, dental braces should not cause problems other than distorting images.