MRI Brain — acute stroke
Whole brain including posterior fossa; intracranial arterial coverage from the vertebral and internal carotid arteries through the circle of Willis when angiography is included.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Suspected acute ischaemic stroke where CT is equivocal or negative and the diagnosis would change management.
- Wake-up stroke or unknown onset time, where the mismatch between a visible diffusion lesion and an as-yet-normal FLAIR is used as a surrogate for lesion age.
- Suspected posterior circulation or brainstem infarction, which CT frequently misses.
- Suspected stroke mimics — seizure, migraine aura, encephalitis, hypoglycaemic injury.
- Suspected arterial dissection as the cause of stroke in a younger patient, adding fat-saturated T1 through the neck.
Technique
- Minimum useful set: DWI with ADC, FLAIR, and a susceptibility-sensitive sequence (SWI or T2*) to detect haemorrhage.
- Intracranial time-of-flight MR angiography is added where large-vessel occlusion is the question.
- Perfusion imaging, where used for late-window selection, is a dynamic susceptibility contrast acquisition requiring a power injector and a rapid gadolinium bolus.
- Sources differ on whether diffusion-FLAIR mismatch or perfusion mismatch should drive late-window thrombectomy selection; both are in use and local pathway wins.
Where it goes wrong
- Choosing MRI when it delays a time-critical decision that CT plus CT angiography would have made sooner.
- Omitting the susceptibility sequence, so haemorrhagic transformation is not seen.
- Reading a diffusion lesion as necessarily acute without the FLAIR comparison the mismatch concept depends on.
- Diffusion signal loss from susceptibility near the skull base masking small brainstem infarcts.
- Screening a confused or aphasic patient inadequately for devices under time pressure — the pathway must not shortcut MR safety.
Clinical questions that reach this study
Known or suspected lung cancer — stagingSuspected acute ischaemic strokeSuspected intracranial haemorrhage (non-traumatic)Suspected subarachnoid haemorrhageFirst unprovoked seizureDrug-resistant epilepsy — pre-surgical assessmentSuspected brain metastasesSuspected primary brain tumourSuspected multiple sclerosis or first demyelinating eventSuspected meningitis or encephalitisHeadache with red flag featuresHeadache without red flags (migraine, tension-type, chronic stable)Suspected normal pressure hydrocephalusCognitive impairment or suspected dementiaHead injury in childrenSuspected inflammatory spinal cord lesion (transverse myelitis)Chronic rhinosinusitis and pre-operative sinus CTSuspected physical abuse in a child — skeletal survey
Contrast
None
- The core acute protocol is unenhanced. Contrast is only involved if contrast-enhanced angiography or perfusion is added, which is a separate local decision.
Acquisition
- Breathing
- Free breathing; the priority is total table time in a time-critical pathway.
- Preparation
- No fasting or bowel preparation for an unenhanced brain study. Establish whether gadolinium is actually needed before booking an IV slot — most brain questions do not require it. Young children and patients unable to keep still for 20-30 minutes need a sedation or general anaesthetic pathway agreed in advance.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- MR safety screening for implants and foreign bodies· radiographer at scan
- Sedation or anaesthesia for a child· nurse pre scan