Article In Brief
New findings suggest a portable, low-field MRI can help assess brain injury at the bedside of critically ill patients. The portability of this device is a benefit, given that the extremely contagious nature of COVID-19 can impose significant impediments to maneuvering critically ill patients within the hospital and decontaminating conventional imaging suites, experts say.
Portable, low-field MRI machines can help evaluate brain injury at the bedside of critically ill patients, suggests a new study published online on September 8 in JAMA Neurology.
The prospective, single-center cohort study followed 50 patients in neuroscience or COVID-19 intensive care units (ICUs) at Yale New Haven Hospital from October 30, 2019, to May 20, 2020.
No adverse events or complications occurred during the setup and use of the portable MRI device in ICU rooms, according to the study investigators at Yale New Haven Hospital who helped develop and deploy the novel bedside neuroimaging tool.
In their first clinical report on the portable device, the researchers noted that although neuroimaging is essential to assessing brain injury in complex clinical care environments, critically ill patients are often too unstable for transport to conventional MRI imaging suites. A transfer could interfere with the operation of monitoring equipment, pose venous access limitations, result in endotracheal tube dislodging, and expose these patients to many other risks.
Compounding the difficulties of transport are infectious diseases such as COVID-19. The extremely contagious nature of this illness can impose significant impediments to maneuvering critically ill patients within the hospital and decontaminating conventional imaging suites, the researchers told Neurology Today.
Furthermore, to ensure patient safety in the presence of high-strength magnetic field scanners [1.5 and 3 Tesla (T)], the spaces housing traditional MRI systems require implementation of strict access controls. “Limited access to timely neuroimaging remains a key structural barrier to effectively monitor the occurrence and progression of neurological injury in intensive care settings,” the authors wrote.
The feasibility of a low-field, portable MRI device lays the groundwork for a potential paradigm shift in neuroimaging for patients in ICUs, they said, adding “recent advances in low-field MRI technology have allowed for the acquisition of clinically meaningful imaging outside of radiology suites and in the presence of ferromagnetic materials at the bedside.”
A portable MRI offers other distinct advantages as well, said Kevin N. Sheth, MD, FAAN, principal study investigator and professor and chief of the division of neurocritical care and emergency neurology at Yale School of Medicine and Yale New Haven Hospital.
“This type of MRI takes up a third of a portable CT footprint. As a result, it can be moved anywhere in the hospital or a physician's office. The fundamental novelty is its true portability,” Dr. Sheth told Neurology Today.
A specially trained technician is not needed to operate the portable MRI device. The machine can be positioned at the patient's bedside and plugged it into a single standard power outlet, the study noted.
Dr. Sheth said future research should look to validate the current findings. “Can we replicate this experience at multiple centers?” he asked. “What are the range of pathologies and pathology characteristics that can be seen? I think those are the kinds of questions which we can now have the opportunity to answer since we've taken this first step.”
Eligible patients in the study had sustained a neurological injury or alteration and, in some, a nasopharyngeal swab result confirmed COVIID-19.
Body size could not extend beyond the scanner's 30-cm vertical opening. Other exclusion criteria included at least one contraindication to undergoing conventional MRI: cardiac pacemakers or defibrillators, intravenous medication pumps, insulin pumps, deep brain stimulators, vagus nerve stimulators, cochlear implants, pregnancy, ongoing extra corporeal membrane oxygenation treatment and cardiorespiratory instability.
“The device dimensions rendered it maneuverable within the confines of an ICU patient room,” the authors noted. “A self-contained motor and driving capability facilitated the deployment of a single device across the institution.”
The study participants all underwent point-of-care MRI examinations. Their pathologies ranged from ischemic stroke to hemorrhagic stroke, subarachnoid hemorrhage, traumatic brain injury, brain tumor, and COVID-19 with altered mental status.
The scans were performed at a median of five days after the patients had been admitted to the ICU. Diagnostic-grade T1-weighted, T2-weighted, T2 fluid-attenuated inversion recovery, and diffusion-weighted imaging sequences were acquired for 37, 48, 45 and 32 patients, respectively.
Of the 30 patients who did not have COVID-19, 29 (97 percent) had neuroimaging findings. Among the COVID-19 group, abnormalities were detected in eight of 20 patients (40 percent).
Eleven patients (55 percent) also underwent conventional neuroimaging (eight, CT; three, MRI). The conventional radiology reports for these patients were similar to the corresponding point-of-care MRI findings.
Due to the low-field strength, ferromagnetic equipment—such as vital sign monitors, intravenous infusion pumps, ventilators, compressed gas tanks, and dialysis machines—could stay in the patient's room. The portable MRI was disinfected with a hospital-approved product after each use.
For patients who did not undergo conventional neuroimaging, point-of-care MRI images were read by a board-certified neuroradiologist, whereas staff neuroradiologists interpreted the conventional scans.
The single-center design and the small number of patients constitute the main limitations of the study. “Prospective multicenter studies in which POC [point-of-care] MRI diagnostic results are compared with conventional computed tomography or MRI results for discrete pathologies are necessary for further validation,” the authors acknowledged. “In addition, this was a cross-sectional study in which patients were imaged at variable points in their hospital course.”
In the era of COVID-19, this study on the feasibility of low-field, portable MRI is particularly timely, said J. Ricardo Carhuapoma, MD, FAHA, FANA, associate professor of neurology, neurosurgery, and anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine.
“COVID-19 adds to the urgency of point-of-care MRI simply because those patients have manifestations of how extremely critically ill one can become,” Dr. Carhuapoma said. “We've had a need for this kind of advanced imaging for quite a long time.”
“Having a portable MRI instead of a portable CT scan in the ICU gives you many advantages,” said Panayiotis N. Varelas, MD, PhD, FAAN, FNCS, professor and chairman of neurology at Albany Medical Center in Albany, NY.
For example, Dr. Varelas cited the capability of visualizing the development of an acute stroke as early as 30 to 40 minutes as opposed to several hours, as well as the absence of radiation. In that respect, “the CT scan is quite inferior to the MRI.”
However, Dr. Varelas pointed out that the study emphasized safety but didn't prove the utility of the portable MRI to the higher degree that he would prefer to see. The images in the published tables also appeared to be first-generation and too granular in quality due to the lower Tesla field, he said.
The investigators used very low magnet strength (0.064 Tesla), which still yielded impressive images, said Joshua P. Klein, MD, PhD, FANA, FAAN, vice chair of clinical affairs in the department of neurology at Brigham and Women's Hospital and associate professor of neurology and radiology at Harvard Medical School.
Resolution and detail, Dr. Klein said, were comparable to current standard-of-care ICU imaging. Nonetheless, he echoed a concern of the study authors in pointing out that, in one patient evaluated with portable MRI, a diffuse subarachnoid hemorrhage was not observed.
“It would have been instructive to include that case” in a graphic illustration to demonstrate “a potential limitation of the low-magnetic-field, portable technique in detecting smaller or more subtle abnormalities,” Dr. Klein said. He also expressed interest in the feasibility of obtaining additional sequences on the low-magnetic-field, portable MRI, including susceptibility-weighted imaging, post-contrast imaging, angiography, and perfusion imaging.
Overall, a potential advantage of portable MRI over portable CT is the enhanced resolution and tissue contrast of MRI and its capability to detect small or subtle abnormalities better than CT, he said. “The most important application of low-magnetic-field, portable MRI in the ICU will be to safely visualize abnormalities that might not otherwise be seen, and for detection of those abnormalities to result in actionable changes in patient care.”
For now, “this exciting proof-of-principle study showed that low-magnetic-field, portable MRI was feasible, safe, and practical in an ICU setting,” Dr. Klein said.
Another advantage? The costs associated with the portable MRI are likely substantially less than the expenses related to the purchase, installation, and operation of conventional MRI, said Zachary Threlkeld, MD, clinical assistant professor of neurology and neurological sciences at Stanford University School of Medicine.
“This has the potential to expand the availability of MRI to hospitals and locations that otherwise lack the considerable resources and demand required to support conventional MRI,” Dr. Threlkeld said.
When Dr. Threlkeld graduated from the University of Kentucky College of Medicine in 2012, he “was taught that there is no such thing as a ‘stat’ MRI for critically ill patients.” Now, he said, “this study challenges that presumption and demonstrates early evidence of feasibility and clinical use of a novel, low magnetic field, portable MRI.”
“With further development,” he added, this technology has the potential to alter clinicians' traditional ways of thinking about MRI capabilities. “Portable MRI brings the imaging suite to the patient instead and allows clinicians to use MRI for patients who might otherwise be unable to receive one,” Dr. Threlkeld said. “Furthermore, portable MRI might allow for more frequent, serial MRI for patients with rapidly evolving neurologic conditions.”
One downside, he said, is that “this portable, low-field MRI has a magnetic field orders of magnitude weaker than a conventional MRI, which allows it to be mobile and to be introduced into a typical ICU room without impractical magnetic precautions. That flexibility, though, is not without disadvantage.”
Nonetheless, given that conventional MRI image quality has improved dramatically over time, Dr. Threlkeld expects more innovation in the coming years. Further research, novel image acquisition and processing methods, and integration of machine learning “will enhance the image quality that low-field devices are capable of producing.”
“The main advantage of low-field, portable MRI for neuroimaging lies in assessing infarcts with diffusion-weighted imaging,” said Marin Darsie, MD, assistant professor of emergency medicine and neurosurgery at the University of Wisconsin School of Medicine and Public Health in Madison, , and her husband, James C. Darsie, MD, a board-certified neuroradiologist at Mercy Health Hospital and Trauma Center in Janesville.
Many other findings also would be apparent on CT scans without contrast. Serial MRI scans could be done to evaluate “evolution of changes over time without concern for ionizing radiation doses (increased lifetime risk of cancer and cataracts),” Dr. Marin Darsie noted.
“The lower barrier for entry (for example, cost and space) of a low-field strength MRI scanner would allow it to be utilized in locations and situations where traditional MRI scanners may not be readily available such as rural settings or places where MRI staffing is not available during the night,” Dr. James Darsie added.
Another factor at play is the extreme challenge of having neurocritical care patients lie flat due to elevations in intracranial pressure from increased venous blood flow into the skull when the head of the patient's bed is flattened. Even with a perfectly efficient setup and scan, these patients often can be positioned flat for less than five minutes and sometimes less than two to three minutes. Many of them will need aggressive treatment before or during the scan to treat occurrences of increased intracranial pressure (ICP).
“I cannot say enough how different it is for a patient with high ICP to be laid flat for less than five minutes compared to the 35 minutes quoted in the article about the portable MRI,” Dr. Marin Darsie said. “Many neurocritical care patients who are very sick would never be able to tolerate lying flat like that.”
At the University of Wisconsin, she added, physicians have access to a “fast stroke screen” MRI, which lasts six to eight minutes and offers a lot more information than the portable MRI scanner.
She pointed out that, during an infectious disease outbreak, extensive cleaning protocols can take a conventional MRI scanner or CT scanner out of commission for upwards of two hours. “This can slow down the entire hospital's flow when it comes to obtaining timely imaging for critically ill patients,” Dr. Marin Darsie said.
“Also, in regards to patients with illnesses which are spread in an airborne fashion, there is no truly safe way to transport them through the halls” without potentially exposing everyone else to contagious particles.
“Given the systems-wide issues that the COVID-19 pandemic is forcing hospital systems to grapple with, a portable MRI scanner may provide valuable information for individual patients, while also keeping the larger system safe from an infection control perspective,” Drs. Marin and James Darsie wrote in an email to Neurology Today.
Dr. Sheth reported grants from the American Heart Association and Hyperfine Research Inc. 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. Drs. Threlkeld, James Darsie and Marin Darsie had no relevant disclosures. Dr. Klein receives compensation from SAGE Publishing for serving as editor-in-chief of The Neurohospitalist, compensation and royalties from McGraw-Hill for serving as co-author of the textbook Adams and Victor's Principles of Neurology, 10th and 11th Editions; compensation from Audio Digest Foundation for serving as scientific director of the Neurology Board Review Course, as well as compensation and travel expenses for serving as section chair, course director, lecturer, author, and committee member from the American Academy of Neurology Institute. Dr. Klein has also received compensation for work as a medical expert from multiple law firms. Dr. Varelas is an advisor for UCB and serves on the speakers bureau for Portola.