A new generation of low-field MR systems is becoming more common in hospital settings where they are primarily used in neuroICUs to assess critically ill patients on devices such as ventilators, and who cannot be as easily transported to MR rooms. The 0.064 T devices are portable and range from $50,000 – $100,000 — making them significantly cheaper than the $3 million or more price tags attached to standard 1.5 T and 3.0 T systems.
Despite their advantages, these systems have lower magnetic fields and therefore, produce images with weaker quality than the standard systems. Even the use of gadolinium as a contrast agent is a no-go, due to debates around its long-term toxicity and the fact that these low-field MR scanners require 1,000 times the approved amount by the FDA.
This may change soon, following an investigation by researchers at Massachusetts General Hospital and the University of Sydney in Australia into the use of SPIONs for such scans. Short for superparamagnetic iron oxide nanoparticles, SPIONs are FDA-approved for treating certain cases of anemia, and have been proved to be safe. They are also 3,000 times more magnetic than conventional MR contrast agents, a fact that the researchers assert makes them ideal for low-field scanners, as they can amplify their magnetic fields.
“There do not exist contrast agents that perform well enough at low magnetic fields,” physicist Matthew Rosen, director of the Low-field MR and Hyperpolarized Media Laboratory at the MGH Martinos Center for Biomedical Imaging told HCB News. “Adding contrast to low magnetic field scanners allows the full gamut of the type of scans that people do with high-field. It's a very standard workflow of an oncologist who is trying to study the progress of some brain cancer. They would say, ‘let’s order these imaging sequences, plus contrast.’ And so the plus contrast part is something you can now do at low field.”
Physicists David Waddington, the lead author of the study, and Zdenka Kuncic, both from the University of Sydney, tested their approach in a trial involving healthy lab rats that were scanned with Rosen’s homemade ultra-low-field MR scanner. Each subject was given an initial scan without the contrast agent and another with it. Images from both scans were compared, with kidneys, liver and other organs in the contrast-enhanced scan glowing more brightly than in the non-contrast one.
While they require FDA approval for use as contrast agents, doctors can use SPIONs off-label with low-field MR. Waddington and Kuncic are also studying the use of specially coated SPIONs to see if they would allow MR to detect malignant tumors.
Rosen hopes that a human trial investigating the use of SPION-based contrast agents with low-field MR will happen sooner rather than later, in order to move toward a reality where low-cost MR is more affordable, with higher-quality imaging.
“I’ve been reaching out to clinical collaborators here,” he said. “There is a lot of enthusiasm for that. People I have spoken to, mostly in neurology, are very interested in this. Probably something like this will happen sooner rather than later. The people who are doing low field MR, such as folks at Yale and people on Long Island at Northwell Health, are all very excited about boosting the obtainable imaging information from this new imaging modality.”
The study was supported by the Australian Academy of Technological Sciences and Engineering (ATSE) Global Connections Fund Bridging Grant, the University of Sydney Nano Institute and the Cancer Institute of NSW Early Career Fellowship.