Noncontrast CT, CTA, Perfusion, and Imaging Workflow

Imaging answers the first safety question

The first imaging question in suspected acute stroke is: is there blood? A noncontrast computed tomography (CT) scan is fast, widely available, and highly sensitive for acute intracranial hemorrhage, so it is the standard gate before thrombolytic therapy. MRI (diffusion-weighted imaging) can also exclude hemorrhage and detect early ischemia, but it is usually less available and slower for immediate code-stroke workflow, so CT remains the default.

Do not overinterpret a normal early CT. In the first hours of an ischemic stroke, the scan is frequently normal or shows only subtle early signs (loss of gray-white differentiation, insular ribbon sign, a hyperdense MCA sign, sulcal effacement). A clean CT means there is no hemorrhage — it does not mean there is no stroke.

The ASPECTS score (Alberta Stroke Program Early CT Score, 10 down to 0) grades the extent of early MCA-territory ischemia: a score of 10 is normal, each region with early ischemic change subtracts a point, and a higher (preserved) score predicts better reperfusion outcomes. ASPECTS therefore informs both thrombolytic and thrombectomy decisions. The correct nursing response to a normal CT is to keep the stroke pathway moving, not to reassure the patient that nothing is wrong.

The same scan is also read for an established large infarct, midline shift, or mass effect, any of which changes the risk-benefit balance of reperfusion.

Time goals are system goals

Get With The Guidelines and the Target: Stroke initiative track door-to-imaging and door-to-treatment intervals. The benchmarks the nurse should know are door-to-CT 25 minutes or less and door-to-needle 60 minutes or less (with stretch goals of 45 and even 30 minutes), achieved in 75 percent or more of treated patients. Every 15-minute reduction in door-to-needle time is associated with roughly a 4 percent better functional outcome and lower mortality.

SCRN questions rarely ask the nurse to recite registry fields; they test the behaviors behind the metrics — EMS prenotification, single-call activation, direct-to-CT transport, parallel lab collection, and early pharmacy involvement.

CTA and large-vessel occlusion

A patient with aphasia, forced gaze deviation, dense hemiparesis, severe neglect, or decreased consciousness may have a large-vessel occlusion (LVO) — typically the internal carotid terminus, the M1/M2 middle cerebral artery, or the basilar artery. CT angiography (CTA) acquired from the aortic arch through the vertex localizes the occlusion and defines collateral and access anatomy, directly supporting thrombectomy and transfer decisions. The nurse does not decide eligibility independently but must recognize why vascular imaging and transfer calls are urgent.

Contrast questions are practical nursing questions. Verify allergies, prior contrast reaction, IV adequacy (an 18-20 gauge antecubital line is often needed for power injection), and known kidney disease per local protocol. Importantly, current guidance is that CTA should not be delayed to wait for serum creatinine in a patient without a history of renal impairment when LVO is suspected — the time cost outweighs the small contrast-nephropathy risk. Do not let low-yield paperwork delay imaging once the team has accepted the risk-benefit plan.

Perfusion and extended windows

CT perfusion (CTP) and MRI mismatch imaging estimate the infarct core (tissue already irreversibly damaged) versus the ischemic penumbra (at-risk but salvageable tissue). A small core with a large penumbra is the favorable "mismatch" that justifies reperfusion beyond the earliest window. This imaging underpins the extended-window evidence:

• DAWN trial: thrombectomy 6-24 hours from LKW for anterior LVO with a clinical-core mismatch.
• DEFUSE-3 trial: thrombectomy 6-16 hours from LKW for anterior LVO with perfusion-core mismatch.
• WAKE-UP / EXTEND / extended-window thrombolysis: IV thrombolysis up to 9 hours, or in unknown-onset/wake-up stroke, selected by DWI-FLAIR mismatch or CTP.

For the SCRN nurse, the point is not to quote trial names at the bedside but to keep LKW, witnessed-onset time, neurologic severity, premorbid function, and imaging results linked so the stroke specialist can decide rapidly.

Nursing workflow in and around the scanner

Before transport, confirm monitoring, IV access, glucose, vital signs, and airway stability, and that the patient can lie flat and still. During imaging, watch for vomiting, agitation, deteriorating mental status, or airway compromise — a patient who cannot protect the airway may need management before scanning. After imaging, ensure the results reach the decision-makers immediately; a scan that is completed but not communicated has not yet helped the patient. Closed-loop reporting of "no hemorrhage, CTA shows M1 occlusion, perfusion favorable" is what converts pixels into treatment.

Finally, anticipate the next imaging need. A patient who deteriorates after thrombolysis or thrombectomy returns to noncontrast CT to look for hemorrhagic transformation; a patient with malignant edema may need serial scans to track midline shift. The nurse who has already cleared transport, monitoring, and the airway plan makes that repeat scan happen in minutes rather than the delay that costs salvageable brain. Treat imaging as a continuous service the patient may need repeatedly, not a single checkbox completed on arrival.