Magnetic resonance imaging (MRI) technology is a mainstay of modern medicine — at least, for those who can access it. MRI field scanners can now provide more detailed brain images than ever, yet for much of the world they remain out of reach .
However, a less powerful and less resource-intensive MRI may give more people access to lifesaving imaging resources. According to a new study published in the April 22 issue of Science Advances, neuroimages obtained using a portable magnetic resonance imaging (pMRI) machine with very low magnetic field strength detected areas of dead tissue in the brains of 50 stroke patients.
Doctors revised treatment plans for two intensive care COVID-19 patients based on stroke damage revealed by pMRI. The results support the idea that low-field pMRI may offer a clinically viable technology for stroke patients and could potentially help democratize access to critical medical equipment in resource-scarce environments.
"MRI is a cornerstone in the evaluation of stroke, but there is limited access to conventional high-field MRI due to the size, cost and safety considerations," said W. Taylor Kimberly, chief of the division of neurocritical care at Massachusetts General Hospital, an associate professor of neurology at Harvard Medical School, and a co-corresponding author of the study. "The portable MRI brings the imaging technology to the patient bedside, and has the potential to expand access due to its lower cost and portability."
Expanding Access
MRI field scanners, which use radio waves to create detailed renditions of organs and tissues, have grown increasingly powerful since they were first approved in the mid-1980s. But for this imaging technology, with great power comes great production expense, cryogen consumption (used to cool the magnets), specialized personnel needs and electrical power usage. Many lower- and middle-income countries do not have the resources to support these conventional MRI scanners. Even more basic radiology services, such as X-ray imaging, are in short supply in many nations. According to the World Health Organization, an estimated two-thirds of the world's population does not have adequate access to these services. Disparities in radiologists, who read imaging scans, also abound. A 2016 article in The Atlantic points out a single hospital in Boston has 126 radiologists while the entire country of Liberia has just two.
Even the wealth of imaging technologies in the U.S. are concentrated in urban areas, leaving segments of the population without access to radiology services. Stroke centers, for example, are usually located in more densely populated parts of the country. When someone in a rural community experiences a stroke, she may need to be helicoptered to a center.
"When we first began working on portable MRI, we thought about potential clinical use case scenarios," said Kimberly. "While we had a number of ideas, we became most excited about the potential to use portable MRI for the diagnosis and monitoring of stroke, an area where repeat imaging is commonly needed for management decisions."
"Our long-term goal is to help get treatments to as many people as possible, as quickly as possible," added Kevin Sheth, a professor of neurology and neurosurgery at the Yale School of Medicine and vice chair for clinical and translational research in the departments of neurology and neurosurgery. "Many groups have been working on the physics and engineering principles behind low magnetic field-based imaging for years. In recent years, this work has moved to the clinical setting. Our group was privileged to be the first in the world to deploy such a device in the clinical setting, and this paper is one of several we have published."
Detecting Damage in Ischemic Stroke
Previously, the researchers demonstrated that low-field pMRI may be used to evaluate and monitor brain injuries from hemorrhagic strokes, caused by bleeding in the brain. However, there had been few assessments of how the technology performs with ischemic strokes, caused by reduced blood flow, which account for 87% of all strokes.
To investigate how pMRI technology performs with this common type of stroke, Matthew Yuen, an M.D.-Ph.D. candidate at Yale University School of Medicine and the first author of the study, and colleagues used low-field pMRI to obtain bedside intracranial imaging for 50 stroke patients in a hospital emergency department, an inpatient neuroscience intensive care unit, and a COVID-19 intensive care unit. The pMRI device, which Sheth described as "a little shorter than an average adult and just as wide as a standard doorway," is controlled with an iPad and employs magnets with less than 1% of the strength of those found in the largest clinical units.
For 90% of the patients, pMRI successfully identified dead tissue in affected areas of the brain, which was also imaged using standard-of-care neuroimaging. Two intensive care COVID-19 patients who could not be transported to locations with conventional non-contrast computed tomography (NCCT) or MRI were imaged by pMRI at their hospital bedsides. The technology detected damage from otherwise unknown ischemic strokes for these patients, ultimately leading to adjustments in the patients' treatment plans after the findings were confirmed with conventional neuroimaging. The findings demonstrate the utility of this comparatively weak MRI for assessing stroke damage in intensive care settings.
"We were gratified to see that we could detect strokes of different sizes at different time points," said Sheth. "At the same time, while our ability to detect stroke is very good, it is clear that significant work needs to be done in order for the device to be used in routine clinical practice."
"The cost of the device will need to come down further in order for large numbers of patients and providers to be able to use it, and there will need to be a greater understanding of the clinical workflow and staffing needed to use the device," he added. "There will also need to be very large datasets developed and openly shared, collected from a variety of settings, so that the medical and scientific community can have confidence in the validity of image interpretation."