Suspected acute ischaemic stroke

ACR AC Cerebrovascular Diseases-Stroke (2024); NICE NG128; DAWN/DEFUSE-3/WAKE-UP

A staged hyperacute sequence rather than a single study: unenhanced CT to exclude haemorrhage and permit thrombolysis, angiography to find a treatable occlusion, and perfusion only where it will decide thrombectomy in the extended window.

Sudden focal neurological deficit within a treatment window, or on waking. The vetting question is almost never whether to scan but how far along the sequence to go, and how fast.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Time since onset

Decides thrombolysis and thrombectomy windows, testicular salvage, and whether an ischaemic limb is still salvageable.

Focal neurological deficit

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Head — Unenhanced

CT Head

What we'd amend, and why

The unenhanced scan comes first for one reason: thrombolysis cannot be given until intracranial haemorrhage has been excluded, and haemorrhage and infarction are clinically indistinguishable at the bedside. It is fast, needs no cannula and no renal information, and it simultaneously grades early ischaemic change and shows a hyperdense occluded vessel. Nothing further in this pathway is interpretable without it.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayhyperacute — Suspected hyperacute stroke — onset not stated, including wake-up and unwitnessed presentations
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(1)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.

Worth asking the referrer (2)

None of these hold the request up. They sharpen the protocol or the plan that follows.

What time was the patient last known to be at their neurological baseline?
It determines whether perfusion imaging is added and whether the unknown-onset MRI mismatch route is relevant. It does not gate the unenhanced CT, which happens regardless.
Is the patient a potential candidate for mechanical thrombectomy?
Angiography and perfusion exist to select for an intervention. If the patient could never receive it, the sequence stops after the unenhanced CT.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Focal deficit within the treatment window — CT and angiography in one visit

Role	Study & protocol	Why this answers the question
First line	CT Head CT Head — Unenhanced usually appropriate	Nothing changes about the unenhanced study: haemorrhage still has to be excluded before thrombolysis and it is still the fastest way to do it. What changes is that a stated deficit inside the treatment window removes any reason to stage the visit. Scan now, and do not wait on a cannula, a creatinine or a bed.
First line	CT Angiogram — Intracranial (Circle of Willis) CT Angiogram — Intracranial Arteries	Co-equal with the unenhanced series in this specific patient rather than a later rung, because in a deficit measured in minutes the two acquisitions are one visit to the scanner. A referrer who writes "CT head and CT angiogram" for a patient with a deficit two hours old has reasoned exactly as NICE NG128 does, and answering them with a sequencing correction costs the second attendance the card elsewhere warns about. The angiographic question is unchanged — is there a proximal occlusion a catheter can reach — and it only matters where thrombectomy is possible at all.
Reasonable alternative	CT Angiogram — Carotid and Vertebral (Arch to Vertex) CT Angiogram — Aortic Arch to Vertex	Arch-to-vertex coverage answers the intracranial question as well, and adds the cervical access route and any tandem or dissecting lesion. Choosing it instead of a purely intracranial run costs nothing diagnostically.
Problem solving	CT Perfusion — Brain CT Perfusion — Brain	Inside six hours the core-penumbra distinction rarely decides anything that the plain and vascular studies have not already decided, so perfusion stays a problem-solving addition here rather than a routine component. It earns its contrast and its dose in the extended window, not in this one.

Haemodynamic instability, airway compromise or a falling conscious level take precedence over every step here — the patient is resuscitated on the way to the scanner, not instead of it.

Beyond six hours from time last known well — perfusion or diffusion decides selection

Role	Study & protocol	Why this answers the question
First line	CT Head CT Head — Unenhanced usually appropriate	Still first, and for the same reason: haemorrhage cannot be excluded any other way and everything downstream is uninterpretable without it. Beyond six hours it also carries more weight than it did, because established hypodensity is now visible and the extent of it is part of deciding whether any intervention remains sensible.
Second line	CT Perfusion — Brain CT Perfusion — Brain	This is the window NICE NG128 attaches perfusion to, and the point of it is that the window has not closed. Beyond six hours the core-penumbra mismatch is what SELECTS a patient for thrombectomy rather than refining a decision already made, and the selection extends to 24 hours from time last known well: DAWN selected on a clinical deficit disproportionate to a small infarct core, DEFUSE-3 on a perfusion mismatch, and both showed large treatment effects at 6 to 16 and 6 to 24 hours. A deficit of 12 or 18 hours therefore belongs in the scanner, not in a bed. Beyond roughly 24 hours the selection question generally closes and the study becomes descriptive; at that point the extra contrast and dose need a reason of their own — with the single exception of basilar occlusion, where a later intervention is still routinely considered and the vascular study rather than the perfusion study is what answers it.
Second line	CT Angiogram — Intracranial (Circle of Willis) CT Angiogram — Intracranial Arteries	Still tied to thrombectomy candidacy rather than to the diagnosis, and acquired in the same visit as the perfusion study when both are wanted. In a patient who could never receive the intervention the sequence stops after the unenhanced scan. Cover the vertebrobasilar system as well as the anterior circulation: basilar occlusion is the occlusion most often presenting late, most often normal on unenhanced CT, and the one in which a late intervention is still worth making.
Second line	MRI Brain MRI Brain — acute stroke	The diffusion-FLAIR mismatch is a surrogate for lesion age, which is precisely what is missing in an unwitnessed or wake-up presentation — a diffusion-positive, FLAIR-negative lesion indicates an onset within roughly 4.5 hours and, in the WAKE-UP trial, selected patients who benefited from thrombolysis. Diffusion also finds the small posterior fossa and brainstem infarcts that CT will not show at any time point. In a deficit measured in days rather than hours the question has moved from treatment selection to diagnosis and mechanism, and MRI answers that far better than perfusion does.

An onset time beyond the window narrows what treatment can achieve; it never converts the unenhanced CT into an elective study, and up to 24 hours it does not close the thrombectomy question either.

Suspected hyperacute stroke — onset not stated, including wake-up and unwitnessed presentations

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Head CT Head — Unenhanced usually appropriate	The unenhanced scan comes first for one reason: thrombolysis cannot be given until intracranial haemorrhage has been excluded, and haemorrhage and infarction are clinically indistinguishable at the bedside. It is fast, needs no cannula and no renal information, and it simultaneously grades early ischaemic change and shows a hyperdense occluded vessel. Nothing further in this pathway is interpretable without it.
Second line	CT Angiogram — Intracranial (Circle of Willis) CT Angiogram — Intracranial Arteries	Angiography answers a different question from the unenhanced scan: is there a proximal occlusion a catheter can reach. NICE NG128 attaches this step to thrombectomy candidacy rather than to the diagnosis of stroke, which is why it is a second step and not a routine addition. Acquire it in the same visit to the scanner as the unenhanced series, since a second attendance costs salvageable brain.
Reasonable alternative	CT Angiogram — Carotid and Vertebral (Arch to Vertex) CT Angiogram — Aortic Arch to Vertex	Arch-to-vertex coverage is the better acquisition where tandem cervical disease, dissection or a difficult access route would change the interventional plan. It answers the intracranial question as well, so choosing it instead of a purely intracranial run costs nothing diagnostically.
Problem solving	CT Perfusion — Brain CT Perfusion — Brain	Perfusion separates irreversibly infarcted core from hypoperfused but salvageable tissue. It is worth the extra contrast and dose only when that distinction decides an intervention — typically thrombectomy considered beyond six hours from onset, or where the onset time is unknown. Adding it to a case that will never go to the angiography suite is dose and delay without benefit.
Second line	MRI Brain MRI Brain — acute stroke	On this arm the onset time is not stated, and the commonest reason for that is that nobody knows it — the patient woke with the deficit or was found. That patient is not outside treatment: a lesion visible on diffusion and not yet visible on FLAIR indicates an onset within roughly 4.5 hours, and in the WAKE-UP trial thrombolysis selected on that mismatch alone improved outcome. Diffusion is also far more sensitive than CT for small, posterior fossa and brainstem infarcts, which is the group in which a normal CT is most often read as excluding stroke, and it identifies the mimics — seizure, encephalitis, hypoglycaemic injury — that CT cannot. Its cost is time, which is why it follows rather than replaces the unenhanced CT; it is not a reason to skip it.

Every step after the first is optional and conditional. The failure mode in practice is not omitting perfusion; it is delaying the unenhanced CT while the later steps are arranged.
Ask for the time last known well rather than the time the deficit was noticed. Where nobody knows it, the pathway does not stop: diffusion-FLAIR mismatch stands in for the clock for thrombolysis, and perfusion or clinical-core mismatch does the same for thrombectomy out to 24 hours.

Pitfalls

Delaying the unenhanced CT to arrange angiography or perfusion. The sequence is ordered for a reason, and the first step is the one with a treatment attached to it.
Accepting a request for CT perfusion alone. Perfusion maps are uninterpretable without the unenhanced study and the vascular study alongside them.
Treating a normal CT as excluding stroke. Early infarction is frequently invisible, and posterior fossa infarcts are routinely missed on CT.
Treating a wake-up or unwitnessed stroke as being outside all treatment. Unknown onset is a reason to image differently — diffusion-FLAIR mismatch for thrombolysis, perfusion or clinical-core mismatch for thrombectomy — not a reason to stop at an unenhanced scan and admit the patient.
Standing a patient down from thrombectomy assessment because the deficit is more than six hours old. DAWN and DEFUSE-3 extended selection to 24 hours from time last known well, and the imaging on this pathway is what performs that selection.
Missing basilar occlusion. A fluctuating or depressed conscious level, or a brainstem syndrome with a low NIHSS and a normal unenhanced CT, is the classic presentation; it needs the vertebrobasilar system covered on the angiographic run and diffusion where CT is normal, and it is the occlusion in which a late intervention is still worth making.
Withholding contrast-enhanced angiography over an unknown eGFR in a thrombectomy candidate, which trades a small and largely theoretical renal risk for a large and immediate neurological one.
Requests written as "CT head and CT angiogram" in a patient with a deficit measured in days rather than hours. The pathway is built for the treatment window, and outside it the question, and the right study, change.

Priors — what to pull first

Any prior brain imaging transforms interpretation of early ischaemic change: old infarcts and chronic small vessel disease are routinely over-called as acute on a first study.
A previous CT angiogram or carotid Doppler establishes whether an occlusion is new or chronic, which changes thrombectomy suitability.

What makes a good request

A good request states time last known well, the deficit, and whether the patient is a candidate for thrombolysis, thrombectomy or neither. Those three facts select the whole pathway.
Time last known well, not time of discovery, is what drives the window. Wake-up presentations are treated as unknown onset, not as onset at waking.
The two treatments have different clocks and the request should not conflate them. Intravenous thrombolysis is a decision made inside 4.5 hours of time last known well; mechanical thrombectomy is routine inside 6 hours and extends to 24 hours in patients selected on imaging, on the DAWN clinical-core mismatch and DEFUSE-3 perfusion mismatch criteria. An onset of 12 or 18 hours is therefore not "too late" — it is precisely the situation the perfusion study exists to adjudicate, and treating it as outside all treatment is the commonest way a thrombectomy candidate is lost.
A wake-up or unwitnessed stroke is not excluded from treatment either. A lesion that is visible on diffusion and not yet visible on FLAIR is a validated surrogate for an onset within about 4.5 hours, and the WAKE-UP trial showed benefit from thrombolysis selected on that mismatch alone. Unknown onset is a reason to image differently, not a reason to stop.
Posterior circulation strokes are the ones this pathway misses. Vertigo, diplopia, dysarthria, ataxia, bilateral or crossed signs and a fluctuating conscious level score low on the NIHSS, are frequently invisible on unenhanced CT at any time point, and basilar occlusion carries a justified intervention window well beyond the anterior circulation one. Suspect it explicitly, cover the vertebrobasilar system on the angiographic run rather than stopping at the circle of Willis, and use diffusion when CT is normal and the story is posterior.
NICE NG128 makes the angiographic step conditional on thrombectomy candidacy, and adds perfusion (CT or MR equivalent) when thrombectomy is being considered beyond six hours from onset.

Scoring this once it is done

The classification and risk tools this question ends in.

ASPECTS - Alberta Stroke Program Early CT Score Posterior Circulation ASPECTS (pc-ASPECTS)mTICI / TICI Reperfusion Grade ABCD2 Score (TIA Stroke Risk)Carotid Stenosis (NASCET & ECST)RoPE Score (PFO in Cryptogenic Stroke)

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Head — Unenhanced CT Angiogram — Intracranial Arteries CT Angiogram — Aortic Arch to Vertex CT Perfusion — Brain MRI Brain — acute stroke

Confirm locally

CT Head — Unenhanced: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.