A new type of MRI scanner that works at ultra-low magnetic fields—thousands of times weaker than a standard hospital machine—is being tested on stroke patients within minutes of their arrival at the emergency department. This matters because current MRI scanners are large, expensive, and immobile. Many small or rural hospitals lack them entirely, and even in major centres, patients must be transported to a dedicated room, which delays treatment. For stroke, where every minute counts, that delay can mean the difference between recovery and permanent brain damage. The new scanner sits next to a research 3T MRI and is a five-minute walk from the emergency department, allowing researchers to image patients as close to symptom onset as possible. If successful, this pilot data will guide the development of a portable, head-only device that could eventually be placed in ambulances or emergency departments. That would transform pre-hospital stroke care—enabling paramedics to distinguish between a clot and a bleed before deciding on treatment, and extending access to advanced brain imaging to communities that currently have none.
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Unmet need: Portable, safe, effective and affordable imaging for ischaemic stroke (IS) which may also be applicable to other acquired brain injuries (e.g. intracerebral haemorrhage (ICH) and traumatic brain injury). This is relevant in the pre-hospital setting: 1) NICE approval of tenecteplase bolus rather than alteplase infusion for treatment of IS within 4.5 hours simplifying administration pre-hospital1 2) the INTERACT 4 study found rapid blood pressure lowering in the ambulance was associated with better outcomes in ICH patients but worse outcomes in IS patients, highlighting the need for diagnostic imaging before treatment2. 3) Increasing understanding of early haematoma expansion in ICH and thus the need for early treatment initiationx. This is relevant for hospital settings: i) Lower rates of thrombolysis in areas outside large urban areas3. Small or rural hospitals have limited advanced imaging (CT perfusion, MRI), impeding assessment of suitability for recanalisation therapies particularly where time of onset is unknown3. ii) Increased interest in portable, low-field MRI (LF-MRI) as a solution to safety, cost and access concerns of existing MRI technologies as witnessed by recent studies using low fixed-field scanners (SWOOP (Hyperfine, 64mT))4. Field-cycling imaging (FCI) is a unique imaging technology that employs fast field-cycling at ultra-low magnetic field (ULF)5. The former explores the magnetic spectrum and molecular dynamics in vivo by measuring changes in T1 relaxation time constant of tissues over a wide range of magnetic field strengths, rapidly switching between different fields during the pulse sequence. This closely relates to water dynamics over time scales that complement diffusion-weighted MRI and represents a potential new imaging biomarker6. We have identified subacute ischaemic stroke at magnetic fields as low as 0.2mT (Fig 1), with differences in nuclear magnetic resonance dispersion (NMRD) profile between stroke and matched contralateral brain7. We have also accurately identified ICH (Fig 2)8, peri-haematomal oedema8, and small vessel disease9 when compared to 3T MRI. We hypothesise that characterising intracellular and extracellular water dynamics using NMRD in acute ischaemic stroke will identify early infarct and distinguish between salvageable and core infarct tissue. A new multi-slice FCI prototype which can cycle between 200 and <0.2 mT with much-improved voxel size (<1mm) has been constructed next to a research 3T MRI, and five minutes from the Emergency Department (ED) (Fig 3). We will image patients as close to onset of stroke symptoms as practical to test whether FCI can identify and quantify acute tissue changes when compared to 3T MRI. This pilot data will inform development of a next generation head-specific portable low-field device which could eventually be placed in ambulances or EDs. A stroke survivor has contributed to the application and is a co-applicant (CM). Participant feedback from previous studies has contributed to improved patient comfort and scanning environment, including an adapted head coil to reduce claustrophobia. This proposal fits James Lind priorities10. Five patient representatives visited the new scanner and shared a vision of improving access to brain imaging.
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