← Back to Browse
Ask AleraHome
CT
BrainDemonstration data

CT Perfusion — Acute Stroke

CT perfusion (CTP) is a dynamic contrast-enhanced technique that quantifies cerebral haemodynamics in acute ischaemic stroke. By deriving cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time-to-maximum (Tmax), it distinguishes infarct core from salvageable penumbra and, with automated software, informs thrombectomy eligibility in extended windows.

Indications

  • Acute anterior-circulation large-vessel occlusion for thrombectomy selection in the 6-24 hour window
  • Stroke with unknown time of onset (e.g. wake-up stroke) requiring tissue-based selection
  • Confirmation and quantification of ischaemic penumbra beyond standard treatment windows
  • Problem solving in suspected stroke mimics and posterior circulation ischaemia

Contraindications & Cautions

  • Severe iodinated contrast allergy without adequate premedication
  • Significant renal impairment (weigh urgency of reperfusion decision against risk)
  • Established large infarct on non-contrast CT where perfusion adds little
  • Haemorrhage on non-contrast CT (perfusion not indicated as first test)

Patient Preparation

  • Preceding non-contrast head CT to exclude haemorrhage and large established infarct
  • Secure large-bore intravenous access (18-20 G) for power injection
  • Rapid renal function assessment per institutional acute stroke protocol
  • Head immobilisation to minimise motion during the dynamic acquisition

Technique & Parameters

  • Bolus of 35-50 mL iodinated contrast at 4-6 mL/s followed by saline flush
  • Dynamic cine acquisition (typically 45-70 seconds) with adequate temporal sampling to capture first pass
  • Coverage of the vascular territory of interest (whole-brain coverage where available)
  • Post-processing with deconvolution to generate CBF, CBV, MTT and Tmax parametric maps
  • Automated software (e.g. RAPID) for core and penumbra volumetrics and mismatch calculation

Systematic Review

  • Verify arterial input and venous output functions and adequacy of the bolus
  • Inspect CBF and Tmax maps for the region of hypoperfusion
  • Define core as relative CBF <30% and penumbra as Tmax >6 s
  • Compute mismatch volume (penumbra minus core) and mismatch ratio
  • Correlate with CT angiography occlusion site and non-contrast CT

Key Findings & Significance

  • Ischaemic core: markedly reduced CBF (rCBF <30%) with matched reduced CBV
  • Penumbra: prolonged Tmax >6 s with preserved or increased CBV (autoregulation)
  • Prolonged MTT and Tmax delineating the total ischaemic territory
  • Favourable mismatch profile (e.g. core <70 mL, mismatch ratio ≥1.8, mismatch volume ≥15 mL)
  • Luxury perfusion or reperfusion hyperaemia after recanalisation

Differential Considerations

  • Seizure-related hyperperfusion or postictal hypoperfusion mimicking ischaemia
  • Chronic small-vessel ischaemia and prior infarct causing baseline perfusion asymmetry
  • Migraine aura with cortical spreading hypoperfusion
  • Technical artefact from poor bolus, motion or truncated acquisition
  • Venous or watershed hypoperfusion unrelated to acute large-vessel occlusion

Pearls & Pitfalls

  • CTP thresholds are software and processing dependent; use validated, consistent parameters
  • Core volume can be overestimated in the very early time window (ghost infarct core)
  • Always interpret CTP alongside non-contrast CT and CT angiography, never in isolation
  • DEFUSE 3 and DAWN trial criteria underpin extended-window thrombectomy selection

Structured Report

  • Report ischaemic core and penumbra volumes and the mismatch ratio
  • State the occlusion site correlated with CT angiography
  • Comment on whether the profile meets institutional thrombectomy criteria
  • Note technical adequacy and any confounders (motion, bolus timing)
  • Provide an integrated conclusion combining CT, CTA and CTP findings

References

  • Albers GW et al. DEFUSE 3: Thrombectomy for Stroke with Perfusion-Imaging Selection, NEJM
  • Nogueira RG et al. DAWN: Thrombectomy 6 to 24 Hours after Stroke with Clinical-Infarct Mismatch, NEJM
  • Radiographics: Vagal A et al. Automated CT Perfusion Imaging for Acute Ischemic Stroke
  • AHA/ASA Guidelines for the Early Management of Patients with Acute Ischemic Stroke

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.