CT Head Without Contrast

Indications

• Acute stroke (ischemic vs hemorrhagic triage prior to thrombolysis/thrombectomy)
• Head trauma / traumatic brain injury, suspected intracranial hemorrhage
• Acute headache, thunderclap headache (suspected subarachnoid hemorrhage)
• Altered mental status, new neurologic deficit, seizure
• Suspected hydrocephalus / shunt evaluation
• Mental status change in known mass or post-op follow-up

Patient prep

• No specific prep; no NPO required
• Remove hairpins, earrings, dentures, hearing aids and other metallic/dense objects from scan field
• Position supine, head first, in head holder; immobilize head
• Confirm patient can lie still; sedation occasionally needed in agitated/pediatric patients

Contrast

Technique

• Supine, head first; gantry angled along the orbitomeatal (or supraorbital-meatal) line to minimize lens dose, or acquire helically and reformat
• Coverage: foramen magnum / skull base through vertex
• Helical or sequential/axial acquisition; 120 kV typical; mAs per scanner with automatic exposure control (≈250-350 effective mAs)
• Iterative reconstruction to reduce dose/noise
• Reconstruct soft-tissue (brain) kernel at 4-5 mm axial and bone kernel at thin section; reformat coronal and sagittal
• No breath-hold required

Series / Sequences

Key points

• First-line in acute stroke to exclude hemorrhage before thrombolysis; assess for early ischemic change (loss of gray-white differentiation, insular ribbon sign, hyperdense vessel sign) and use ASPECTS scoring
• Subarachnoid hemorrhage sensitivity is highest within 6 hours; consider LP or vessel imaging if negative but clinically suspected
• Use narrow stroke windows to improve gray-white contrast
• Keep gantry tilt or reformat to spare the orbital lenses; thin bone recon essential for trauma
• If acute large-vessel occlusion suspected, typically proceed to CTA +/- CT perfusion

References