Portable Low-Field MRI Promising in Critically Ill Patients

Pauline Anderson

September 11, 2020

A portable, low-field magnetic resonance imaging (MRI) device provides convenient, safe, and accurate bedside neuroimaging in critically ill patients, results from a small new study suggest.

Dr Kevin Sheth

The novel device could help fill an important gap in obtaining clinically useful neuroimaging in patients for whom access to traditional MRI scanners is challenging, the researchers say.

Lead study author Kevin N. Sheth, MD, professor of neurology and neurosurgery, and division chief, Neurocritical Care and Emergency Neurology, Yale University School of Medicine, New Haven, Connecticut, called the new results "provocative."

"We can see things with this device that are clinically relevant, and that's exciting," Sheth told Medscape Medical News.

While it remains to be determined where the device "can and can't be used," it won't be long before the technology is readily available, said Sheth. "That day is coming very soon."

The study was published online September 8 in JAMA Neurology.

Time-sensitive neuroimaging is the cornerstone of triage and treatment for patients with an acute neurological illness. This often involves MRI systems that use high-strength magnetic fields in controlled environments and require rigid safety precautions and highly trained technicians.

But these high-field scanners are largely inaccessible to critically ill patients due to risks of transporting them to imaging suites. And for critically ill patients with COVID-19, the highly contagious nature of their illness not only significantly limits access to imaging suites but requires decontamination of these environments.

Recent advances in MRI technology allow data acquisition at low magnetic field strength and scanning outside strictly controlled environments. "We recently developed and deployed a novel bedside neuroimaging solution, for which this is our first clinical report," the authors write. 

The result is a portable low-field (0.064-Tesla [T]) MRI device for use at the bedside in neuroscience intensive care units (ICUs) and COVID-19 ICUs.

It has an 8-channel head coil and uses a biplanar, 3-axis gradient system with a peak amplitude of 26 mT/m (on the z-axis) and 25 mT/m (on the x-axis and y-axis). Operators can use a computer interface (iPad Pro, third generation; Apple) to control scan parameters.

The strength of this portable device is "many-fold weaker" than a traditional MRI that has a much higher magnetic field (1.5T or 3T), said Sheth.

"You can't take an oxygen tank into a secure MRI room or it would fly across room," and even a credit card and glasses are banned objects in this environment, he said.

"But this portable MRI can go into a clinical environment where you have ventilators and oxygen tanks."

No Coolants

As this point-of-care (POC) MRI scanner uses a permanent relatively weak magnet, there's no need for cryogens used to cool the magnet in traditional MRI systems. And because the scanner uses less than 1650 W of power, it can be plugged into a standard outlet.

The device is small enough to be easily maneuvered within the confines of an ICU patient room.

The study included 50 patients (32% women, mean age 59 years) admitted to the neuroscience ICU or COVID-19 ICU at Yale New Haven Hospital. Of these, nine patients presented with ischemic stroke, 12 with hemorrhagic stroke, two with subarachnoid hemorrhage, three with traumatic brain injury, four with a brain tumor, and 20 with COVID-19 infection and altered mental status.

At a median of 5 days after ICU admission, researchers carried out examinations at the bedside using the prototype scanner.

For the duration of the examination, 18 of the patients with COVID-19 were mechanically ventilated and one required high-flow oxygen. Three patients were receiving continuous kidney replacement therapy.

The examination, including set-up and scanning, lasted a mean of 35 minutes and 40 seconds, which is comparable to a traditional MRI, said Sheth.

Deploying the portable device in an ICU room did not result in adverse events or complications in any of the patients.

Researchers obtained patient demographics, clinical course characteristics, and available conventional neuroimaging information from electronic medical records.

In the 30 patients without COVID-19, neuroimaging findings were detected in 97%. Twenty-nine patients (97%) also received conventional imaging: six had computed tomography (CT) and 23 had MRI.

In these non-COVID patients, all POC MRI findings were in agreement with available conventional radiology reports, except that one patient had a diffuse subarachnoid hemorrhage that was not observed on POC MRI.

"There are some scenarios — subarachnoid hemorrhage is one of them, and very small or microhemorrhage is another — where we don't have great evidence that this device can detect those just yet," said Sheth.

But the device did uncover a previously undetected, small-volume right cerebellum infarct in a patient in their 40s with cardiac arrest who was too unstable to be transported to conventional imaging.

"That's encouraging," although it's unclear "what the limits are" with this device, said Sheth. "Can it pick up a stroke as tiny as 1 cm every time, and is it possible to detect even smaller strokes?"

For the patients with COVID-19, neuroimaging findings were observed in 40%, including intracranial hemorrhage in one, cerebral infarction in three, diffuse cerebral edema in one, and leukoencephalopathy in three patients.

About 55% of the patients with COVID-19 received conventional neuroimaging (eight had CT and three MRI). In these, all POC MRI findings were in agreement with conventional radiology reports.

For example, the portable device found a previously undetected, large hemispheric infarction of the left middle cerebral artery in a patient with COVID-19 in their 50s who was paralyzed and sedated. The patient, said Sheth, was scheduled for a tracheostomy and feeding tube placement the following day.  

"When we did this imaging with the portable MRI, we found that half the brain had a huge stroke," which was confirmed with conventional neuroimaging.


Resolution Sufficient

In terms of resolution, the images generated by the portable MRI "are sufficiently good that we can still make out brain pathology in patients who have strokes and brain hemorrhages," said Sheth.

But it's not clear from this analysis if the images are consistent and "capture the entire brain," he added. 

Sheth said that the portable device should not be compared to a traditional MRI "because normally, you can't get an MRI in the ICU."

And he stressed that the resolution continues "to get better and better through a number of hardware and software improvements."

The device, which has been approved by the Food and Drug Administration, is "starting to make the migration to clinical care" from the research setting, said Sheth. He and his colleagues are using the device in the emergency department and are investigating what other environments would be conducive to its use.

"There will always be situations and places where patients can't get an MRI," said Sheth. In addition to patients with COVID-19, this could include those presenting at a small rural hospital or an outpatient clinic, or anywhere in a developing country.

The cost is also an attractive feature. Sheth estimates the device will have a price tag of between $50,000 and $100,000, compared to "a couple of million" dollars for a traditional MRI scanner.

But there are issues still to be ironed out in terms of use in the clinical context, said Sheth. In addition to determining where it can and can't be used, experts have to figure out billing parameters and integration into the electronic record.

Nevertheless, Seth said he's "optimistic that we will start to see this in some form in clinical practice within the next couple of years."

Study limitations included the single-center design and the small number of patients imaged.

Bringing Imaging to the Patient

Asked to comment on the study for Medscape Medical News, Brian Silver, MD, chair and professor in the Department of Neurology, University of Massachusetts Medical School, Worcester, said it's "an excellent first step in bringing imaging to the patient, rather than the patient to imaging." 

The resolution of images with the portable scanner isn't as good as that with a conventional scanner, but Silver sees this as a "trade-off" to allow the device to be used at the patient's bedside. And most experts would consider the resolution adequate when used in this setting, he said.

"Looking at the images, they are good enough to identify injuries that are greater than 5 mm. For smaller lesions, you would probably need a 1.5 to 3T."

In addition to a bedside device being convenient, and needing no cooling after use, it has a "much lower" risk that its magnetic fields will "trigger" other devices, noted Silver. "The authors describe a safety radius of 79 cm, which is far less than that of a conventional MRI."

Silver noted that several other investigators are developing similar technologies. He himself has a patent for a lightweight wearable device that uses magnetic waves, designed for patients with a brain injury. 

Also commenting for Medscape Medical News, Ralph L. Sacco MD, professor and Olemberg Chair of Neurology, and senior associate dean for clinical & translational science, Miller School of Medicine, University of Miami, Florida, and immediate past president, American Academy of Neurology, called the device "a real technological breakthrough."

"This low-field MRI is safe enough to use in the ICU without disrupting other equipment and not endangering the patient by having to be transported to another part of the hospital."

The "excellent" images provided by the portable MRI device "help improve diagnosis and management of ICU patients," said Sacco. 

"As technology continues to accelerate, we can expect more advances in our bedside imaging capabilities."

Sheth has reported receiving grants from the American Heart Association, National Institutes of Health, and Hyperfine Research Inc (the company that developed the device technology) during the conduct of the study, and grants from Bard, Biogen, and Novartis; personal fees from Zoll; and other support from Alva outside the submitted work. Silver has a patent for a device that uses magnetic waves. Sacco has reported no relevant financial relationships.

JAMA Neurol. Published online September 8, 2020. Article

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