mCTA as the default decision tool:
Multiphase CTA replaces binary CTA/CTP thinking by providing sufficient flow dynamics and collateral information for most stroke patients, enabling fast, confident triage without routine perfusion imaging.
Head‑to‑heart imaging in the acute phase:
Extending the first arterial mCTA phase to include the heart allows early detection of cardioembolic sources during initial stroke imaging, accelerating etiologic classification and secondary prevention decisions.
CT perfusion used selectively, not routinely:
CTP is preserved as a high‑value problem‑solver for complex vascular or clinical presentations, where automated volumetry adds decisive physiological insight without compromising time‑to‑treatment.
Figure 2. Multiphase CT angiography (mCTA) acquired in three phases. The upper row displays maximum intensity projection (MIP) images with a slice thickness of 25 mm at the level of the circle of Willis, while the lower row shows parenchymal images with a slice thickness of 5 mm at the level of the basal ganglia. From left to right, the images represent the early arterial phase (phase 1), the arteriovenous phase (phase 2), and the venous phase (phase 3). An occlusion of the right middle cerebral artery (MCA) is visible in the distal M1 segment. There is delayed contrast filling in the right MCA territory with a one-phase delay compared to the left side, but good contrast filling is observed in the later phases.
Protocol
"Stroke patients at Karolinska University Hospital in Solna are primarily examined using the NAEOTOM Alpha CT scanner. The scan protocol is designed to be fast and effective and consists of three main components: non-contrast-enhanced CT (NECT), multiphase CT angiography (mCTA), and CT perfusion (CTP). NECT and mCTA are always performed, whereas CTP is omitted if intracranial bleeding is detected. In cases of bleeding, mCTA is used to exclude potential vascular malformations, such as aneurysms, arteriovenous malformations, or arteriovenous fistulas, as the source of hemorrhage. Additionally, when bleeding is present, the mCTA acquisition is limited to the brain with all three phases, as additional coverage from the heart is not required. A summary of the stroke scan protocol is provided in Table 1, and the individual scan series along with their corresponding reconstructions are discussed in detail in this section."
Reconstruction & Post‑Processing Details
Exam | Reconstruction / Processing |
|---|
NECT | • VNC + Iodine maps (1 mm Qr44 QIR4) |
|---|
• Soft brain MPR: 0.8 mm Hr40 QIR4, 67 keV | |
• Bone kernel: 0.4 mm Hr72 QIR2, 768×768 | |
• Automated MPRs via syngo.via | |
mCTA | • Vessel recon: 0.4 mm Hv56 QIR4 T3D |
|---|
• Automated thick MIPs (axial/coronal/sagittal) | |
• Parenchymal recon: 5 mm Qr44 QIR4 53 keV (recently 2 mm Hr36) | |
CTP | • 30 volumes / 45 s |
|---|
• 5 mm Hr40 QIR4 T3D | |
• Fully automated perfusion maps (penumbra, core, mismatch) via Rapid Results Technology | |
Contrast Injection Protocols
Exam | Contrast Protocol |
|---|
mCTA | 80 ml Visipaque 320 @ 6 ml /s (13.3 s) |
|---|
- 80 ml NaCl @ 8 ml /s || CTP | 42 ml Visipaque 320 @ 7 ml /s
- 80 ml NaCl @ 8 ml /s |
Clinical Use Logic (Protocol Rules)
Component | Rule at Karolinska |
|---|
NECT | Always performed |
|---|
mCTA | Always performed |
|---|
Heart coverage | Included in Phase 1 unless hemorrhage present |
|---|
CTP | Performed only if no hemorrhage and case is complex / equivocal |
|---|
Bleeding present | mCTA limited to brain only; CTP skipped |
|---|
Szum et al. Optimizing Acute Stroke Diagnostics with Photon-counting CT: Balancing Multiphase CT Angiography, Perfusion, and Cardioembolic Assessment. Magnetom Flash. ESOC 2026.
