The force is strong in this one
Do not underestimate the strength of the magnetic fields generated by an MRI scan.
PETALING JAYA: Magnetic resonance imaging (MRI) has always been thought of as one of the safest diagnostic imaging procedure, although it’s strong magnetic field can prove to be dangerous to the unwary.
One of the misconceptions about MRI scanners is that they (the magnetic field) can be easily switched on and off, said Universiti Malaya Professor of Medical Physics Dr Ng Kwan Hoong.
It is a misperception that may lull people onto the road of carelessness and negligence.
“We cannot see the presence of magnetic fields, so we often underestimate its power,” he said.
The magnetic field strength of a fridge magnet is 0.005 Tesla, while the magnetic field strength of an MRI scanner can be 300 times that much, depending on the model.
Dr Ng’s motto is “MRI is safe, but if something goes wrong, it can go very wrong”, and he created an “alternate” acronym for MRI, which is Metal Results (in) Injury.
A man in India was killed this year when he brought a metal oxygen tank into the MRI room after being told by a medical staff member that the MRI machine has been “switched off ”.
However, the magnetic force of the superconducting magnet coil in an MRI machine cannot simply be “turned off ”, according to Dr Ng.
“The only way to do so would be to ramp down the machine, which is done by calling the vendor to shut down the magnet.
“The vendor would have to come and release the coolants, which are the nitrogen and helium gas, from the machine.
“These are harmless gases, but very expensive. By letting these gases out, the magnet – which is a very expensive component of the machine – warms down to room temperature and loses its magnetic property,” he said.
Dr Ng said the case in India is not the first MRI-related death.
In 2001, a six-year-old boy in New York died when a metal oxygen tank crushed his skull as it hurtled across the room towards the machine’s magnetic field.
According to Dr Ng, there have been cases of near fatalities, including in Malaysia, where many cases go unreported. In one case, a spanner flew across the room and
Universiti Malaya Professor of Medical Physics Dr Ng Kwan Hoong said one of the misconceptions about MRI scanners is that they can be easily ‘switched off’. grazed the ear of a patient.
He said there are potential hazards that come mainly from the machine’s three different types of magnetic fields, which are static, gradient, and radiofrequency (RF) electromagnetic fields.
“The static magnetic fields could cause ferromagnetic metal objects to become airborne projectiles.
“Ferromagnetic metal implants or fragments in the body may twist and move, causing internal injury.
“The gradient and radiofrequency (RF) electromagnetic fields do not lead to fatalities, but they could cause injuries.
“RF electromagnetic fields could cause the tissue to heat up or electrical burns, while gradient magnetic fields could cause nerve stimulation,” he said.
Comprehensive safety guidelines are not something that MRI procedures lack, but the enforcement of such practices are another matter.
“Most MRI-related incidents have been due to deficiencies in screening methods and/or lack of properly controlling access of potentially harmful objects to the MRI room.
“We don’t have a culture where consciousness of safety is built in. We are not conscientious about safety matters,” he said.
MRI-related accidents, he added, continue to occur in Malaysia due to various factors.
“More MRI scanners are being installed, even in small towns. More patients are also being scanned and more non-radiologists are also working with MRI machines.
“Now companies are also manufacturing MRI scanners with higher magnetic field strengths, as they can produce better images,” he said.
He listed out some safety measures that need to be in place, such as labelling items which are MR-safe, i.e. items that are not ferromagnetic.
Big clear signs in the MRI suite, he said, are needed to indicate which zones are safe for entry, and to delineate the extent of the machine’s magnetic fields.
He added that proper education and training on MRI procedures and hospital policy is also crucial, and proper briefings must be conducted for patients.
Stringent screening methods to ensure that if it is suitable for patients to undergo MRI scans are also vital, said Dr Ng.
For instance, those with cardiac pacemakers, aneurism clips and breast tissue implants should inform their doctors and check with the radiologist first before going for an MRI scan.
He also added that for MRI in children and pregnant women, radiologists have to justify that the scan is indicated, or necessary to provide diagnosis or help in the management of the case.
“There is limited scientific evidence on the risk to a foetus in the case of a pregnant woman, so caution is needed,” he said.