The new method hits a sample with a 30-millitesla magnetic field, about 100 times weaker than is normally used in MRI. The device then uses a stronger 46-microtesla magnetic field - about the same as the Earth's magnetic field - to capture images of the sample.
"The cost of MRI can be reduced dramatically," New Scientist quoted Vadim Zotev of Los Alamos National Laboratory in New Mexico, US, as saying. The new system employs several ultra-sensitive sensors called super-conducting quantum interference devices (SQUIDs), which have to be kept at very low temperatures.
"The most expensive part of our system is the liquid helium cryostat, which costs about 20,000 dollars," Zotev added. Ultra-low field MRI scanning was first performed with a single SQUID in 2004 by a group led by John Clarke at University of California, Berkeley, US, but this only allowed objects about the size of an apple to be scanned.
However, the new device uses seven SQUIDs and can scan much larger objects. MRI systems in the clinic today require a patient to be slotted into a long, cylindrical tube. Ultra-low field MRI machines can be much more open.
"Microtesla MRI is more suitable for surgical environment than high-field MRI," Zotev said. "Some medical equipment can be conveniently placed inside [the scanner]," including surgical robots, Zotev added. Today's MRI machines can also be problematic for people with metal implants, since intense magnetic fields can move or heat them causing damage to surrounding tissue.
Experiments have revealed that ultra-low field MRI can image materials even when metal is placed near the magnets (Journal of Magnetic Resonance, vol.179 p.146).
However, the new device hasn't been tested on animals or people with metal implants yet. "It would be wrong to claim that it is absolutely safe," Zotev said. Since the new device also doubles as magnetoencephalography (MEG) machine, by picking up the feeble magnetic fields from electrical activity in the brain, it could perhaps let surgeons more easily identify areas of the brain with abnormal activity, such as in epilepsy.
"This is the main advantage of the new set-up. It's a nice step forward," Clarke said.