Rapidly restoring blood flow to the brain in patients with stroke caused by a blocked blood vessel in the brain is the key to reducing disability. Current treatments often leave small blocked arteries that cannot be safely opened with mechanical clot removal devices. Furthermore, stagnant flow limits access of clot-dissolving medication to the clot. This trial tests iron nanoparticles (similar to iron infused to replace low body stores but injected directly into the brain artery upstream of the blockage) combined with an external rotating magnet that draws the nanoparticles towards the clot, overcoming stagnant blood flow. The aim is to bring fresh blood which contains naturally-occurring clot-dissolving substances, and any clot-dissolving medication that may be circulating, to the surface of the clot with the aim of restoring blood flow to the brain. The trial will recruit up to 30 patients. All will receive injection of nanoparticles via an angiogram (small tube inserted into a leg or arm artery and fed up into the brain artery under Xray control). The procedure takes 30min and the degree of success in opening the artery at the end of procedure is the primary outcome, combined with an absence of symptomatic brain bleeding at 24h.

Inclusion Criteria:

• Patients presenting with ischemic stroke within 24 hours of the time they were last known to be well
• Patient's age is ≥18 years
• Legal requirements for consent as per local legislative requirements are satisfied.
• Distal medium vessel intracranial arterial occlusion visible on CT-angiography, MR-angiography or catheter digital subtraction angiography (DSA) in the middle cerebral, anterior or posterior cerebral artery. The occlusion may be primary or secondary (ie following initial mechanical thrombectomy of a large vessel occlusion)

Exclusion Criteria:

• Intracranial hemorrhage (ICH) identified by CT or MRI
• Rapidly improving symptoms at the discretion of the investigator
• Pre-stroke mRS score of ≥ 3 (indicating functional dependence)
• Frank hypodensity in >1/3 of the affected arterial territory on non-contrast CT
• CT Perfusion ischemic core volume > 100 ml
• Known automated implantable cardiac defibrillator, pacemaker, cerebral aneurysm clip, cochlear implant, cranial neurostimulator or other device implant that is incompatible with the external magnetic field
• Known allergy or sensitivity to iron
• Known hemochromatosis, or known liver disease such as cirrhosis.
• Known aortic dissection
• Suspected septic embolization
• Contra indication to imaging with contrast agents
• Pregnant or lactating women
• Any terminal illness such that patient would not be expected to survive more than 6 months
• Current participation in another investigational drug or device treatment study
• Any condition that, in the judgment of the investigator could impose hazards to the patient if study therapy is initiated or affect the participation of the patient in the study.

Primary outcome assessed by blinded imaging core laboratory. Day 90 modified Rankin scale assessed by central blinded clinician.