The first magnetic resonance imaging (MRI) exam of a live patient was performed on July 3, 1977.1 Since then, the MRI has become an indispensable tool in the detection, diagnosis, and monitoring of various medical conditions. The typical MRI scanner weighs 11-18,000 pounds2, and can be priced at over a million dollars.
MRI machines are generally viewed as stationary diagnostic tools, with a waitlist of days in both inpatient and outpatient settings. This perception, however, is being challenged by the MedTech company Hyperfine. Their FDA approved Swoop device is transforming the perceived capabilities of MRI machines. The system is less than five feet tall, three feet wide, and weighs approximately 1,400 pounds.3 The compact design allows this portable MRI to be wheeled around the hospital to complete exams, rather than requiring patients to be transported to the exam. Other notable advantages to a portable MRI includes a lower cost and better safety profile for at-risk populations.4
While there are many advantages to the portable design, this MRI is NOT the same as a traditional MRI. This scanner uses a 0.064 Tesla magnetic field,3 which is almost 1/50th the strength of a standard 3 Tesla MRI that is present in most large hospitals. This means that image resolution and field of view is reduced when compared to a standard MRI, which limits the capabilities of this technology.4
One of the clinical promises of low-field portable MRI involves high-acuity brain imaging. When it comes to brain injury, time is an important parameter. MRI is the most sensitive and specific imaging modality for diagnosing acute stroke.5 Due to volume constraints and costs of MRI, however, these conditions are commonly evaluated with computed tomography (CT) scanners, which are fast and available in most hospitals, but have the consequence of exposing the patient to ionizing radiation.
A research group at Johns Hopkins has been investigating the utility of portable MRI in a population that poses many challenges to diagnostic imaging in acute brain injury. This retrospective analysis of a prospective study was published in Diagnostics in March of 2024, and aimed to understand the potential value of low-field portable MRI in detecting acute brain injury in patients on extracorporeal membrane oxygenation (ECMO).6 Patients supported by ECMO are contraindicated from traditional MRI, and are often at risk of injury during transport through the hospital for imaging.7 This group analyzed patients on ECMO that were evaluated for acute brain injury with both CT and portable MRI.
The findings of this study are promising but limited in power. Their initial cohort included 46 patients, and acute brain injury was observed in 17 of the patients.6 Overall, portable MRI outperformed head CT in the detection of acute brain injury. Portable MRI detected double the ischemic events as the CT, but half as many hemorrhagic events.
These results seem promising, but there are multiple glaring issues in the design of this study, the most obvious of which is the sample size. In addition, the gap in time between the two exams leads to a possibility that an acute event occurred after CT but before MRI.6 Lastly, MRI is the reference standard in detecting ischemic events, which wasn’t used to validate the sensitivity of each imaging modality. This means that both low-field portable MRI and CT could have missed an acute ischemic event, further blurring the results of the study.
While drawing concrete conclusions from this study is not possible, there are positive takeaways. The inspiring aspect of this study lies in its implications for future research. The potential benefits of a diagnostic scanner that offers greater accessibility than a CT scanner with improved diagnostic sensitivity and lower risks to the patient is not to be ignored.
References
1. July, 1977: MRI Uses Fundamental Physics for Clinical Diagnosis. Accessed April 22, 2024. http://www.aps.org/publications/apsnews/200607/history.cfm
2. Foo TKF, Laskaris E, Verilyea M, et al. Lightweight, Compact, and High-Performance 3T MR System for Imaging the Brain and Extremities. Magn Reson Med. 2018;80(5):2232-2245. doi:10.1002/mrm.27175
3. Details and Specs: Swoop® Portable MR Imaging® System. Accessed April 22, 2024. https://hyperfine.io/swoop/details-and-specifications
4. Arnold TC, Freeman CW, Litt B, Stein JM. Low‐field MRI: Clinical promise and challenges. J Magn Reson Imaging. 2023;57(1):25-44. doi:10.1002/jmri.28408
5. Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke – PMC. Accessed April 22, 2024. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2905927/
6. Cho SM, Khanduja S, Kim J, et al. Detection of Acute Brain Injury in Intensive Care Unit Patients on ECMO Support Using Ultra-Low-Field Portable MRI: A Retrospective Analysis Compared to Head CT. Diagnostics (Basel). 2024;14(6):606. doi:10.3390/diagnostics14060606
7. Parmentier-Decrucq E, Poissy J, Favory R, et al. Adverse events during intrahospital transport of critically ill patients: incidence and risk factors. Ann Intensive Care. 2013;3(1):10. doi:10.1186/2110-5820-3-10
Benson Lagusis is a member of the University of Arizona College of Medicine - Phoenix Class of 2026. He graduated with a B.S. in Exercise Science from Northern Arizona University before earning a Master's degree in Biomedical Sciences from Midwestern University. Benson played baseball in college, and is interested in sports medicine and health promotion/education. During his free time, Benson is an avid hiker, reader, and Netflix binge-watcher.