From Imaging Challenges to Opportunities: Portable MRI in Low- and Middle-Income Countries
Ahmed Altaf *, Aly Hamza *, Ali Azan *, Omar Islam ‡, Edmond A Knopp †, Khan Mohammed Siddiqui †, Syed Ather Enam *
* Department of Neurosurgery, Aga Khan University Hospital, Karachi 74800, Pakistan
‡ Department of Diagnostic Radiology, Kingston Health Sciences Centre, Kingston, ON, Canada,
†Hyperfine, Inc., Guilford, CT, USA
Corresponding author: Syed Ather Enam (ather.enam@aku.edu)
Keywords: Portable MRI, Low-field MRI, Neuroimaging, Global health, LMIC (low- and middle-income countries), magnetic resonance imaging, diagnostic imaging, developing countries
January 4, 2025
Abstract
Traditional high-field magnetic resonance imaging (MRI) scanners, while offering unparalleled imaging capabilities, largely remain inaccessible to the developing world due to the substantial costs, size, and infrastructure requirements. The recent advent of ultra-low-field portable MRI (ULF pMRI) technology brings new hope for expanding medical imaging access in low- and middle-income countries (LMICs). Compared to traditional MRIs, pMRI scanners eliminate resource-intensive requirements, like shielded rooms, promising expanded imaging access for a resource-limited settings as a result of its portability. However, the use of ULF pMRI has certain drawbacks to consider. The reduced field strength of the scanner compromises on the image resolution and lower signal to noise ratio (SNR). The trade-off with diagnostic accuracy often leads necessitate follow-up scans with a high-field MRI, This review examines pMRI technology and its implications for LMIC healthcare. We explore the range of pMRI technologies, applications, benefits, and limitations. pMRI shows particular promise for expanding life-saving neuroimaging for conditions like stroke. Experts estimate that pMRI could expand neuroimaging access to a vast majority of underserved people in LMICs. Realizing this potential requires overcoming challenges like lack of trained personnel, high costs, and unreliable power shortages. The regular servicing and maintenance of portable MRI machines are critical but can strain limited budgets in low- and middle-income countries (LMICs) due to the cost of spare parts and repairs. Portable MRI machines have comparatively lower image quality, which can hinder the detection of smaller lesions and the accurate tracking of disease progression or treatment effectiveness. Operating and interpreting portable MRI scans require specialized expertise, and the scarcity of skilled technicians in resource-constrained regions poses a significant challenge. Ongoing research aims to address these barriers to integration into LMIC healthcare systems. In conclusion, while promising to improve equity, pMRI implementation faces obstacles. Focused efforts to advance scanner design alongside clinical expertise and infrastructure building could enable pMRI to transform diagnostic capabilities in LMICs. We aim to constructively inform the discourse on improving accessibility, underscoring the potential of pMRI to impact healthcare outcomes in LMICs.
Introduction
Medical imaging is a cornerstone of modern healthcare, revolutionizing the way medical professionals diagnose and treat a wide range of conditions. The impact of medical imaging is evidenced by the fact that the inventors of three of these major modalities have received Nobel prizes for their pioneering works [1]. By providing a non-invasive modality to visualize and assess the anatomical and physiological aspects of the body, medical imaging has been instrumental in helping clinicians diagnose a vast array of conditions, ranging from cancers to cardiac diseases, neurological disorders, and orthopedic injuries. Additionally, they have also been seen as guiding tools during interventional procedures, to ensure the precision and efficacy of surgery and minimize risk. Sequential imaging has been used to assess disease status by monitoring progression or regression and to fine-tune disease management accordingly. This greatly improves patient outcomes and treatment costs [2].
Magnetic resonance imaging (MRI) in particular provides high-resolution imaging of internal structures without exposing the body to high doses of ionizing radiation [3]. This has made it a useful tool in continuous care and radiology-assisted diagnoses in many developed healthcare systems. However, due to a multitude of factors, access to MRI technology has been limited in many low- and middle-income countries (LMICs). The high acquisition cost, followed by maintenance and operative expenses make it a significant burden on financially constrained health systems [4, 5]. Furthermore, poor infrastructure in LMICs also limits access and uptake of MRI systems as these healthcare systems are unable to find resources to house large machines, provide uninterrupted power supply, as well as provide climate-controlled and air-conditioned environments for the machines. The unavailability of skilled technicians and other workforce to operate and understand MRI machines also becomes a barrier to the modality [6]. Moreover, poor transport systems and accessibility in a few LMICs further hinder the availability of healthcare equipment in rural and remote facilities, and subsequently, patients have to make longer trips to more equipped centers in larger cities [7,8]. This stress on time and financial resources to travel long distances, as well as the out-of-pocket expenditure required for healthcare facilities, means that relatively expensive imaging technologies like high-power MRIs remain poorly accessed in large populations around the globe [9].
Low-field MRI scans refer to images below 1.5T, however, multiple sources refer to a smaller limit between 0.01T and 0.1T. For this paper, we are referring to low-field scans as < 1.5T. For this range the available machines in the category of low-field PMRIs are i) Hyperfine Swoop 0.064T, ii) Promaxo 0.066T, iii) Siemens Magneto 0.2T, iv) Synaptive Evry 0.5T v) Siemens Magnetom Free.Max.0.55T, and vi) Aspect Embrace 1.0T [8]. In relevance to this study, the review is kept limited to the Hyperfine Swoop.
The innovative approach of developing ultra-low-field, portable MRI (ULF pMRI) machines may be the glimmer of hope for LMICs. The change in focus from developing larger and more complex MRI scanners to smaller, cheaper, and more portable machines has meant the machine can be transported to and used in locations previously unimaginable.
Objectives and Focus of the Mini-Review
This mini review aims to provide an overview of portable MRI technology and its potential to address the challenges faced by LMICs in accessing advanced medical imaging. We delve into the various portable MRI technologies, their applications in LMICs, the barriers that must be surmounted for successful adoption, recent research and development efforts, and the future prospects of portable MRI as a hope for healthcare in LMICs. By shedding light on the promise and hurdles of portable MRI, we hope to contribute to the broader conversation on improving healthcare equity and accessibility in LMICs.
The Technology Behind Portable MRI Scanners
Low-field MRI technology has been in use since the early 1980s and refers to field strengths below 1.5T. Ultra-low field (ULF) MRI refers to strengths of ≤0.01T, such as the 0.064T Hyperfine Swoop. The development of portable MRI machines has faced significant challenges, including controlling magnetic fields, managing cooling requirements, and reducing both the size and energy consumption of the machine. These factors are essential for ensuring reliable, high-resolution MRI performance. The trade-off between magnetic field strength and device portability is a crucial aspect of this development process.
ULF scanners, while small and more energy-efficient, often struggle with poor signal quality and are more susceptible to field interference. In contrast, high-field scanners provide clearer, higher-resolution images but require extensive shielding and cooling systems, increasing the device’s overall size and energy demands [10]. Figure 1 offers a technical comparison between an ULF pMRI scanner (Hyperfine swoop) and a conventional high-field MRI scanner. A critical factor in developing more portable MRI systems has been optimizing the use of permanent magnets, which were introduced in the 1990s. These magnets offer a more compact design compared to superconducting magnets, especially since they do not require the complex cooling systems associated with superconductors, without compromising too much on image quality. This innovation significantly reduces the size, and energy demands of MRI machines, making them more feasible for portable applications. However, it is important to note that permanent magnets are generally heavier than superconducting magnets and have limitations in achieving higher field strengths.
Fig. 1. Comparison of technical specifications between the ultra-low field portable MRI scanner and a conventional high-field MRI system. The portable MRI has a lower magnetic field strength of only 0.064T compared to the 1.5T/3T field strength typical of full-size clinical MRI scanners.
While permanent magnets have helped reduce the size and energy demands of MRI machines, facilitating their use in portable applications, the shielding requirements are comparable between permanent and superconducting magnets of the same field strength. This is because both types of magnets can produce strong fields that require similar shielding to protect the surrounding environment. The difference often lies in the scanner geometry and the space constraints for siting the equipment.
Innovations such as ring-pair permanent magnet arrays have provided effective solutions to these challenges [11]. Machine learning algorithms have further enhanced image quality by compensating for the interference common in ULF scanners. These advancements have made it feasible to operate portable MRI machines without traditional shielding while still achieving reasonable image quality, enhancing their integration into healthcare settings, particularly in low- and middle-income countries (LMICs) [12]. Although there have been significant improvements, more work is needed to address the remaining technical shortcomings of portable MRI systems [13].
The lower signal in Ultra-Low Field (ULF) MRI can be quantified approximately through equations:
This equation represents the signal S(t) as a product of an encoding matrix Eenc(q, t) and a magnetization vector m(q), where q represents spatial coordinates or variables related to the MRI process.
This equation models the MRI signal as a sum of multiple components, each representing the contribution of a small volume element (voxel) within the object. Each voxel has its own magnetization mq and contributes to the overall signal based on its precession frequency ωq and phase evolution over time. The complex exponential e-j ωq t accounts for the rotation of the magnetization in the transverse plane, reflecting both the real and imaginary parts of the signal that can be detected by the MRI scanner.
By summing these contributions, the total signal Sp(t) represents the combination of all processing magnetization vectors at different spatial locations, giving a comprehensive description of the MRI signal at a specific coil or spatial position over time. This model is fundamental to understanding how MRI signals are formed and processed to generate images.
Enhanced Accessibility: Portable MRI’s Advantage
The reduced energy needs without connection to continuous high power main supply as well as compact size and form of portable MRI machines allows that these machines can be used in settings beyond the controlled environment of a radiology department, especially if it is put on wheels and attached to a mobile power source or supply. These machines have been successfully tested in environments such as offices, outdoors, patient homes, and mobile generators [14]. The development of portable MRI machines, which can be moved on wheels, allows these scanners to operate outside of specially designed radiology facilities. This mobility enables MRI technology to reach remote clinics and areas lacking hospital infrastructure, particularly in low- and middle-income countries (LMICs), where conventional MRI machines would be impractical due to their size, weight, and need for extensive site preparation and power requirements [15].
Another point of view on the portability is the ability to use the scanner in other places around the hospital. The successful use of portable MRIs at the patient bedside and in intra-operative settings are just a couple of exciting examples of pMRI utilization in hospital systems around the globe Figure 2 [16–20]. This is particularly relevant to LMICs as pMRI means a hospital can utilize intraoperative MRIs without setting up designated operative rooms for larger MRI scanners and still achieve imaging that can greatly improve patient outcomes. Other potential uses could include screening of trauma and other patients for cord contusion in the emergency department without the need for moving the patient, rapid head scans for stroke/trauma in an acute setting or an emergency transport vehicle, or even a quick and comparably inexpensive MRI scan as a substitute or adjunct for a subset of orthopedic conventional radiography [21].
Fig. 2. Use of a novel ultra-low field portable MRI system in diverse clinical settings. (A) The portable MRI scanner in use in a clinic setting. The compact size and lack of a strong magnetic field allows flexible positioning in a typical exam room. (B) The MRI scanner brought into an operating room during a surgical procedure. The scanner can obtain images intraoperatively to guide the surgery. (C) Postoperative MRI scan during recovery after surgery. The portable scanner can easily move to the recovery area to monitor patients. (D) MRI scanning at a patient's bedside in a hospital room or ICU. The portable design makes bedside imaging feasible for closer patient monitoring.
Balancing Healthcare Budgets: Costs of pMRI
The cost-saving potential of portable MRIs has been well-studied, with budget impact studies estimating savings of millions of dollars in rural settings of high-income countries [10,15,22]. With persistently poor access to MRI scanners in many LMICs across the globe, these smaller, less costly machines show great promise to reduce disparities in MRI availability and utility worldwide [23,24]. With a large proportion of machines available in West Africa having low field strength, the integration of ULF-strength MRI machines could be a possible option to improve MRI availability.
A systematic review has depicted the cost-effectiveness of using mobile CT and MRI machines with a great decrease in associated cost per scan without any significant difference in performance compared to more expensive fixed models [25]. The same study also talks about the sharing of machines across hospitals in the same vicinity to decrease non-utilization costs and share initial investment. This model can prove beneficial in LMICs where purchasing a machine may be beyond the financial capacities of individual centers, thus enabling hospitals to benefit by dividing financial burdens amongst themselves.
On the other side of operations, lower acquisition and maintenance costs also translate to lower financial stress levied on the patient. With much of the healthcare expenditure in LMICs being out of pocket, to the point where up to one-fourth of the households have to borrow funds or sell valuables in order to afford care, the hope of cheaper imaging shall be held with a tightening grip [26]. The affordability of pMRI, coupled with other factors that increase accessibility, carries the potential to increase MRI use in LMICs.
Prospects and Practicality: pMRI Systems
Beyond LMIC-specific factors, portable MRIs also carry advantages making them useful in many settings globally. The ability to scan patients while in more comfortable or functionally appropriate positions while scanning means improved comfort for the patient, as well as better imaging in settings of studies like weight-bearing patients and kinematic studies [27]. Further, it can be contemplated that the smaller, and open designs of the scanners can be less intimidating and claustrophobic for the patient, particularly in pediatric settings [27,28]. Further, the ULF strength models allow care providers to perform studies on patients with implants and devices that might otherwise be incompatible with larger high-field scanners [27].
Moreover, with the lower power requirements, these mobile devices can be of great use in areas with long power outages. Studies have found that more than one-fourth of MRI centers do not have adequate plans in case of a power cut-off [29]. The availability of portable MRI models with built-in battery backups is again a promising aspect for LMIC integration as these countries can often have prolonged interruptions to the power supply [30].
Additionally, ULF MRI systems have been associated with fewer artifacts secondary to susceptibility than high-field MR systems [31]. Coupled with the role of machine learning algorithms, satisfactory image quality can be achieved to aid diagnoses [32].
Navigating Obstacles: The Limitations of pMRI
Despite the many advantages, portable MRIs still carry many challenges, akin to other MRI systems. The regular servicing of these machines is essential for longevity and accuracy, but the cost of spare parts and repairs can strain the often-limited budgets of healthcare facilities in LMICs. Though these are expected to be lower than costs associated with larger systems, these must be kept in mind before implementation takes place. Furthermore, operating and maintaining MRI equipment necessitates specialized knowledge and skills. In regions where healthcare resources are scarce, finding and retaining technicians with the requisite expertise can be a significant challenge. Training personnel to operate and troubleshoot portable MRI machines effectively requires investment in education and professional development.
Additionally, the image quality of portable MRIs is somewhat inferior to larger, high-field strength systems. Despite being able to identify almost 94% of lesions compared to more complex systems, it may be difficult to spot smaller lesions on portable machines [33]. This resolution can be increased with longer scan times, but this may not always be practical. This marks one of the most important trade-offs between high-field strength and ULF strength machines. Despite the ease of operation of machines, the interpretation of scans requires much expertise as distortions of margins can make it particularly challenging to accurately quantify disease, such as the presence of neurodegenerative disease.
The comparatively lower image quality also complicates the tracking of disease progression or treatment effectiveness, potentially leading to additional healthcare burdens and costs. Figure 3 compares the image quality between ULF pMRI scanner and conventional high field MRI scanner. Balancing the advantages of portability and affordability with the limitation of image quality remains a central challenge in the development and utilization of portable MRI technology, emphasizing the need for ongoing improvements in this field.
Fig. 3. Comparison of image quality between ultra-low field portable MRI and conventional high field MRI. The portable scanner provides adequate image quality for the clinical evaluation of pathology, though with somewhat lower detail than the high field scanner. Overall, the ultra-low field portable MRI provides useful image quality for many clinical applications, with the tradeoff of lower resolution than high-field MRI.
Empowering Diagnostics: Opportunities with pMRI
The use of ULF MRI systems has shown promising results in many studies, including those on patients on extracorporeal membrane oxygenation (ECMO) [34], high-quality brain scans [10], with specialized contrast [35], and even for bedside evaluation [16,17] for hemorrhage [18] and ischemia [36]. This opens avenues for MRI use where it was previously considered impossible or inconvenient. Coupled with the comparatively lower cost per scan, this enables greater use of MRI in LMICs and other healthcare systems with tighter budgets.
Newer model scanners [32] once set up do not require complex technical expertise to run. This is particularly helpful as the depleted and inadequately trained workforce of LMICs often is unable to maintain competency for large and complex MRI systems [37]. With the increase in newer, smarter portable MRIs, and the increased ease of recording scans, portable MRIs are bound to help reduce the burden on the LMIC radiology workforce.
Conclusion
Portable MRI technology presents a promising solution to the longstanding challenge of accessing advanced medical imaging in LMICs. The systems offer affordability, portability, and increased accessibility, making them a valuable addition to healthcare systems in resource-constrained regions. However, it still comes with the compromise of poor image quality, great image distortion, and use in limited pathology. Ongoing research and development efforts are needed to address technical shortcomings and further improve the utility of portable MRIs. With continued innovation and investment, portable MRI carries the potential to improve patient outcomes in LMICs and promote healthcare equity.
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