CT Angiogram — Aortic Arch to Vertex

Aortic arch to the vertex, including the great vessel origins, cervical carotid and vertebral arteries and the intracranial circulation.

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

Carotid territory transient ischaemic attack or minor stroke, to quantify extracranial stenosis before endarterectomy or stenting.
Suspected craniocervical arterial dissection, including after neck trauma or in a young stroke patient.
Suspected vertebrobasilar insufficiency or subclavian steal.
Blunt cerebrovascular injury screening in trauma meeting local criteria.

Technique

Bolus tracking with the monitoring region of interest in the aortic arch or descending aorta; published triggers for cervical work sit around 100-150 HU above baseline, followed by a post-trigger diagnostic delay of roughly 4-8 s. Because the acquisition starts at the arch, that delay is short by design — it exists to let the carotid and vertebral arteries fill, not to wait out a transit time.
A test bolus of about 15-20 mL at the diagnostic injection rate is the alternative where individual transit time is in doubt; the diagnostic delay is then the measured peak arrival time in the arch plus a few seconds. A blind fixed delay of around 15-20 s from the start of injection is the least robust option and is reserved for scanners without tracking.
Scanning caudocranially reduces perivenous streak artefact at the thoracic inlet, which is where the great vessel origins are assessed.
These numbers move with scanner generation: a wide-detector or high-pitch system covers arch to vertex in a few seconds and tolerates a shorter post-trigger delay than an older 16- or 64-slice platform, so a delay copied between scanners is a common source of venous contamination.
Right arm injection keeps dense contrast out of the left brachiocephalic vein and away from the origin of the left common carotid artery.

Where it goes wrong

Dense contrast in the ipsilateral subclavian and brachiocephalic veins produces streak that can simulate or hide an origin stenosis — this is an injection-side problem, not a reconstruction problem.
Heavy calcification blooms on thick maximum-intensity projections and over-calls stenosis; grading should be done on thin axial or curved reformats using consistent criteria.
Scanning too late fills the jugular veins and degrades the intracranial portion.
Swallowing during the acquisition creates a step artefact at exactly the carotid bifurcation.

Clinical questions that reach this study

Carotid imaging after TIA or minor stroke Suspected acute ischaemic stroke

Contrast

Iodinated, intravenous

Typically 40-70 mL of non-ionic iodinated contrast at 4 mL/s or more, followed by a saline chaser of around 25 mL.

Acquisition

Breathing: Quiet respiration or suspended respiration for the arch portion; no swallowing.
Reconstruction: Sub-millimetre axial source images, curved planar reformats along each carotid and vertebral artery, maximum-intensity projections and bone-removal volume rendering.
Preparation: Power-injectable cannula, right antecubital preferred so undiluted contrast in the left brachiocephalic vein does not obscure the great vessel origins. No swallowing during acquisition.

Phases

Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.

Early arterial phaseTypically ~15–25 s after the start of injection (or ~4–8 s after bolus trigger). Confirm locally.
Contrast is in arteries only; parenchyma has barely begun to enhance and veins are unopacified. The transferable principle is that this phase is a road map, not a lesion-detection phase: it defines arterial anatomy, variants, stenoses, dissection flaps and active arterial extravasation, and it deliberately trades away parenchymal contrast to do so. Any solid-organ lesion that depends on parenchymal enhancement difference will be under-called here, so an early arterial series is an addition to a diagnostic phase, never a substitute for one.
CT angiography, bolus-trackedNo fixed delay. A monitoring ROI is placed in the target vessel (commonly the aorta) and acquisition triggers at a set attenuation rise — a ~100 HU threshold is widely used — followed by a short diagnostic delay of a few seconds for table movement and breath-hold instruction. Confirm locally.
This is not a separate physiological phase so much as a technique for hitting one reliably. The transferable principle is that a fixed delay assumes an average circulation, and the patients who most need vascular imaging — the shocked, the failing, the arrhythmic, the aneurysmal — are precisely those whose circulation time is furthest from average. Tracking the bolus in the target vessel replaces that assumption with a measurement, so peak arterial opacification is achieved in the individual patient. The trade-off is that the technique commits the scan to whatever the monitoring ROI sees: a badly placed ROI, a mistimed breath-hold or a threshold reached by a contralateral vein produces a systematically mistimed study rather than a slightly degraded one.

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.

Prior contrast reaction and elective premedication· nurse pre scan
Intravenous access adequate for the planned injection· radiographer at scan
Metformin and iodinated contrast· radiographer at scan
Child-sized technique and contrast dose· radiographer at scan
Kidney function and intravenous iodinated contrast· radiographer at scan