Stroke is the second leading cause of death worldwide, causing annual mortality of about 5.5 million and leaving more than half of the patients affected with some chronic disability. Neuroimaging is an essential tool for the detection, characterization, and prognosis of acute stroke, including ischemic and hemorrhagic subtypes. MRI is commonly used for stroke confirmation and evaluation. However, MRI of stroke patients can be challenging, as transporting patients to specialized radiology suites is associated with numerous cardiovascular and respiratory risks. In traditional imaging pathways, this intrahospital transport of patients can limit timely and safe neuroimaging for critically ill patients with stroke.

In addition, high-field MRI scanners (1.5 to 3 T) are expensive to acquire (~$1 million/T). These devices require specialized technicians to operate them, use considerable electrical power, and require costly infrastructure, such as the cryogens needed to cool the superconducting magnets that make up the scanner. These financial requirements have limited the availability of MRI scanners in low-resource healthcare facilities and rural or remote areas.

A group of researchers from Yale and Harvard recently developed a portable magnetic resonance imaging (pMRI) scanner that operates at very low magnetic field strength and solves many of the limitations of high-field MRI in a novel way. Low-field pMRI is mobile and does not require costly infrastructure or shielding since it operates in environments containing ferromagnetic material and integrates electromagnetic interference rejection. Moreover, pMRI requires minimal operator training as it is easy to use.  For these reasons, low-field pMRI is a substantially more affordable imaging modality than high-field MRI. This portable scanner could be essential in hospitals and health centers that do not have MRI scanners to provide the neuroimaging necessary to detect and characterize a stroke.

A portable bedside solution that facilitates confirmation of diagnosis and assesses the extent and type of stroke can reduce the need for additional procedures, such as surgery, as well as expedite treatment. Stroke patients’ outcomes improve dramatically the faster they receive treatment.  For instance, determining whether the stroke is ischemic (caused by a blocked blood vessel) or hemorrhagic is crucial in deciding on treatment; even treatment for ischemic strokes may be contraindicated for patients with cerebral hemorrhage. However, access to fixed MRI scanners is limited for those living far from large hospitals or in developing countries. Portable scanners represent a new opportunity to mitigate this issue, as they can be used at the patient’s bedside, in ambulances, or in clinics in remote areas.

Another promising advantage of low-field portable MRI is that it makes it more feasible to obtain serial diagnostic images to follow the evolution of stroke to make quick decisions on the fly, which is often unfeasible even in major hospitals due to the high demand for conventional scanners. On the other hand, this medical device opens the door to expanded opportunities for pediatric brain imaging research by reducing the risk of exposure to high field strengths or ionizing radiation. However, pMRI also has limitations in its diagnostic capabilities, even for pathologies other than stroke, due to low image resolution. Nevertheless, this limitation is more a call to take up the challenge to develop more image processing techniques based on deep learning, automated diagnostic algorithms, and advanced image reconstruction approaches to support and enhance the diagnostic capabilities of pMRI and make these diagnostic images available in resource-limited environments.

References

1. Yuen, M. M., Prabhat, A. M., Mazurek, M. H., Chavva, I. R., Crawford, A., Cahn, B. A., … & Sheth, K. N. (2022). Portable, low-field magnetic resonance imaging enables highly accessible and dynamic bedside evaluation of ischemic stroke. Science Advances, 8(16), eabm3952.
2. Hathaway, B (2022). Portable MRIs almost as effective as standard MRIs in detecting strokes. YaleNews
3. Basser, P. (2022). Detection of stroke by portable, low-field MRI: A milestone in medical imaging. Science Advances, 8(16), eabp9307.