01Rapid structural assessment
CT of the head and neck
Non-contrast CT is often the first examination in an acute neurological emergency. Imaging can be extended beyond the brain to extracranial head and neck structures when the symptoms or history indicate it.
Neurological role
- Rapidly identifies intracranial haemorrhage, mass effect, hydrocephalus and many skull or facial fractures.
- Looks for early signs of cerebral infarction and helps decide whether further vascular or perfusion imaging is needed.
- Assesses extracranial structures in selected cases of trauma, infection, tumour or head-and-neck symptoms.
What the patient should know
The scan usually takes only a few minutes. A standard non-contrast head CT needs no injection, but it uses ionising radiation.
Important limitations
A normal early CT does not exclude a small or very recent infarct, and CT has less soft-tissue detail than MRI for many neurological conditions.
02Extra- and intracranial arterial map
CT angiography (CTA)
CTA creates a rapid map of the arteries from the aortic arch and neck vessels to the intracranial circulation after an intravenous injection of iodinated contrast.
Neurological role
- Detects a large-vessel occlusion in acute stroke and shows the route used to plan mechanical thrombectomy.
- Evaluates carotid, vertebral and intracranial stenosis, dissection, aneurysm and other vascular abnormalities.
- Shows vascular anatomy, collateral circulation and relationships to surrounding structures for treatment planning.
What the patient should know
Contrast is injected through an arm vein; a brief feeling of warmth is common. Kidney function, previous contrast reactions and possible pregnancy are checked when relevant.
Important limitations
Calcification, movement and contrast timing can affect accuracy. A complex or very small vascular lesion may still require catheter angiography (DSA).
03Blood flow and tissue viability
CT perfusion (CTP)
CT perfusion follows contrast through the brain and generates colour-coded maps such as cerebral blood flow, cerebral blood volume, mean transit time and Tmax.
Neurological role
- Estimates tissue that is likely already infarcted and tissue that may still be at risk but salvageable in selected patients with acute stroke.
- Supports transfer and reperfusion decisions, including in some patients presenting later or with an uncertain time of onset.
- Adds physiological information to the structural CT and arterial map from CTA.
What the patient should know
A series of images is acquired over a short period while iodinated contrast passes through an arm vein. This adds contrast exposure and radiation to the CT pathway.
Important limitations
Perfusion maps are sensitive to movement, circulation and technical factors. They are never interpreted alone, but together with the examination, non-contrast CT and CTA.
04High-detail tissue characterisation
Magnetic resonance imaging (MRI)
MRI combines different sequences to examine brain, cranial nerves, spine and surrounding soft tissues without ionising radiation.
Neurological role
- Diffusion imaging (DWI/ADC) is highly sensitive to acute ischaemic injury; FLAIR helps characterise oedema and the age and distribution of lesions.
- Susceptibility imaging detects blood products, while dedicated sequences assess tumours, inflammation, demyelination, infection and microvascular disease.
- Targeted protocols can evaluate the cranial nerves, pituitary region, head and neck, spinal cord and spine.
What the patient should know
MRI takes longer than CT and requires the patient to remain still. A safety questionnaire checks implants and metal; gadolinium contrast is used only when it adds useful information.
Important limitations
Movement, severe claustrophobia, some devices and clinical instability can limit MRI. In a time-critical emergency, CT may be faster and more practical.
05Arteries and veins without catheterisation
MR angiography (MRA)
MRA uses MRI techniques to examine extra- and intracranial vessels. Time-of-flight MRA can show arteries without contrast; contrast-enhanced and venous techniques answer other vascular questions.
Neurological role
- Evaluates the carotid, vertebral and intracranial circulation for stenosis, occlusion, aneurysm, dissection or vascular variants.
- Can assess cerebral veins and venous sinuses when venous thrombosis or abnormal drainage is suspected.
- Provides a non-invasive option for diagnosis or follow-up when its detail is appropriate for the clinical question.
What the patient should know
The study is commonly performed as part of the MRI examination. Depending on the question, it may be completed without an injection or with intravenous gadolinium contrast.
Important limitations
Slow or turbulent flow and patient movement can create artefacts or exaggerate a narrowing. Very small or complex lesions may need CTA or DSA for greater detail.
06Time-resolved vascular imaging
4D TWIST arteriovenous MR angiography
4D TWIST is a time-resolved contrast-enhanced MRA technique. It acquires successive three-dimensional volumes as contrast passes from arteries through the capillary phase into veins, adding a dynamic view of blood flow.
Neurological role
- Demonstrates early venous filling and arteriovenous shunting in suspected brain AVMs and dural arteriovenous fistulas.
- Helps show the dominant arterial supply, nidus or fistulous region and venous drainage for non-invasive assessment.
- Can complement planning and follow-up by comparing flow patterns over time without an arterial catheter or X-ray radiation.
What the patient should know
MRI safety screening is required and an intravenous gadolinium injection is usually used. The dynamic series is acquired rapidly while the patient remains still.
Important limitations
Its spatial, temporal and vessel-selective detail is lower than DSA. It complements but does not replace catheter angiography when exact angioarchitecture, definitive confirmation or endovascular treatment planning is required.
