CTA = IV bolus of contrast + helical CT scanner with multislice imaging. Captures arterial & venous phases → detailed imaging of vessels. 3D reconstructions via Maximum Intensity Projection (MIP).

⚙️ Procedure: Timed to peak contrast opacification → circle of Willis + branches + extracranial vessels.

💡 Clinical Applications:

🧠 Detecting basilar artery stroke & clot location for thrombectomy planning.
🌀 Aneurysms: sensitivity 94–98% (>3 mm); 70% if <3 mm.
🩸 Assess thrombus in acute stroke → intra-arterial thrombolysis / thrombectomy guidance.
🔎 Detect dissections, pseudoaneurysms, vasospasm in SAH.

⚠️ Limitations: Less accurate than DSA; risk of contrast nephropathy (esp. renal impairment).

🖼️ CT Perfusion (CTP)

CTP = maps cerebral blood flow dynamics. Often combined with CTA in acute stroke. Generates time-density curves → calculates perfusion parameters.

📊 Key Measures:

💧 CBV (Cerebral Blood Volume): 4–5 ml/100 g tissue.
🚰 CBF (Cerebral Blood Flow): ~50–60 ml/100 g/min (grey matter).
⏱️ MTT (Mean Transit Time): Arterial inflow → venous outflow.
📈 TTP (Time to Peak): Contrast injection → max enhancement.

🧠 Clinical Utility:

Infarct Core ☠️: ↓↓ CBF, ↓↓ CBV, ↑ MTT/Tmax → irreversibly damaged.
Penumbra 🟡: ↓ CBF, preserved/↑ CBV, ↑ MTT/Tmax → salvageable with reperfusion.

Core	Penumbra
⬆️ MTT/Tmax ⬇️⬇️ CBF ⬇️⬇️ CBV	⬆️ MTT/Tmax ⬇️ CBF ~Normal / ↑ CBV

⚠️ Challenges: Results can be affected by arrhythmias, cardiac output, local stenosis. Seizures may mimic hyperperfusion.

📌 Current Use: Increasingly applied in large vessel occlusions & research; more common in comprehensive stroke centres.

🧩 CT in Haemorrhagic Stroke

Non-contrast CT (NCCT) → blood = hyperdense (bright). Sensitivity ~99% in first 24h.

🩸 Findings:

Acute Haemorrhage: Bright hyperdense lesion ± mass effect/midline shift.
SAH: Hazy hyperdensity in sulci/cisterns (Sylvian fissure, interhemispheric fissure, prepontine cistern).
Subdural: Crescent-shaped along brain periphery; chronic → hypodense.
Intraventricular: Blood in ventricles → risk hydrocephalus (ventricular dilatation).

🧲 MRI GRE useful if CT negative after 1–2 weeks.

🎯 Digital Subtraction Angiography (DSA)

DSA = gold standard for vascular detail (aneurysms, AVMs).

⚙️ Procedure: Catheter via femoral artery → contrast → X-ray subtraction imaging.

💡 Clinical Applications:

Detect small aneurysms, AVMs, vasculitis.
Identify bleeding source post-SAH (ruptured aneurysm).
Guide endovascular interventions: coils, stents, embolization.

⚠️ Risks:

~1% stroke risk (embolization).
Bleeding, vascular injury, infection.
Contrast nephropathy (esp. CKD).

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Cerebral Angiography and Perfusion

🖼️ CT Angiography (CTA)

🖼️ CT Perfusion (CTP)

🧩 CT in Haemorrhagic Stroke

🎯 Digital Subtraction Angiography (DSA)

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