MRA Carotid / Neck — contrast-enhanced

Aortic arch and origins of the great vessels to the skull base, usually with intracranial coverage on the same run or as a separate time-of-flight acquisition.

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

Symptomatic carotid territory stroke or transient ischaemic attack where carotid stenosis needs quantifying and ultrasound was equivocal or technically limited.
Suspected cervical arterial dissection, alongside axial fat-saturated T1 through the neck.
Suspected vertebral artery origin disease, which ultrasound cannot assess.
Vascular mapping before neck surgery or intervention.
Large-vessel vasculitis involving the cervical vessels.

Technique

First-pass 3D spoiled gradient-echo acquisition with elliptic-centric or centric k-space ordering so the centre of k-space coincides with peak arterial enhancement.
Bolus timing by automated tracking or a small test bolus; a fixed empirical delay is the least reliable option.
A separate fat-saturated axial T1 sequence through the neck is what actually shows dissection mural haematoma — the angiogram alone can be normal.
Non-contrast alternatives exist and are used where gadolinium is undesirable, but generally give lower confidence at vessel origins.

Where it goes wrong

Mistimed bolus: too early gives arterial signal only at the centre with poor edges, too late gives venous contamination that obscures the carotid bifurcation.
Relying on the angiographic sequence alone in suspected dissection and omitting fat-saturated T1.
Swallowing motion at the moment of the arterial run, which selectively degrades the bifurcation.
Susceptibility from dental work and stents at the very level being interrogated.

Clinical questions that reach this study

Carotid imaging after TIA or minor stroke

Contrast

Gadolinium, intravenous

A macrocyclic gadolinium agent at a typical single dose of about 0.1 mmol/kg, given as a bolus by power injector at around 2-3 mL/s with a 20-30 mL saline chaser at the same rate, timed by bolus tracking or a test bolus.

The rate matters as much as the dose here. Injection rate sets bolus amplitude rather than total enhancement, so a slow injection of a full dose still gives a weak arterial peak; the saline chaser at the same rate is what keeps the tail of the bolus compact.
Timing is the whole study: the arterial run is a single first pass with the centre of k-space acquired at peak arterial enhancement, typically around 15-25 s from the start of injection in a normal circulation, but bolus tracking is preferred precisely because that number moves with cardiac output.

Acquisition

Breathing: Suspended respiration for the arterial acquisition where the patient can manage it; swallowing must be avoided.
Preparation: State the territory: intracranial, cervical, or both — they are different acquisitions with different contrast requirements. For aneurysm surveillance, supply prior imaging and any coil or clip history; hardware degrades time-of-flight locally. IV access is only needed if a contrast-enhanced neck acquisition is planned.

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.

Contrast-enhanced MR angiographyAcquisition is synchronised to bolus arrival in the target vessel, which is short and variable (of the order of 12–25 s from injection in timing-bolus studies), using MR fluoroscopic triggering or a test bolus, with a centric or elliptic-centric k-space order. Confirm locally.
Gadolinium shortens blood T1 so that vessels are bright on a heavily T1-weighted acquisition, independently of flow direction or velocity — which is the whole reason it outperforms non-contrast time-of-flight techniques in slow, turbulent or in-plane flow. The transferable principle is that image contrast is set by the moment the CENTRE of k-space is filled, not by when the acquisition starts or ends: fill the centre while the bolus is arterial and the study is arterial even if sampling continues for another half-minute; fill it a few seconds late and the same raw data yield a venous-contaminated study. Triggering and view ordering are therefore not technical preferences but the phase definition itself.

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
Kidney function and gadolinium-based contrast· radiographer at scan
Intravenous access adequate for the planned injection· radiographer at scan
MR safety screening for implants and foreign bodies· radiographer at scan