CTA Head (Circle of Willis) — Dictation, Appropriateness, and Dose for Residents
1. The Aneurysm Hunt: Acing the Stat CTA Head
Stat CTA head from the ED. 45-year-old with the worst headache of their life. The non-contrast head CT is negative for acute hemorrhage, but the attending wants the aneurysm hunt done yesterday. You need to systematically check the anterior communicating artery, posterior communicating arteries, middle cerebral artery bifurcation, and basilar tip, and you know the neurosurgeons are waiting for your call.
This is a classic scenario where the focused CTA Head (Circle of Willis only) shines. It’s a fast, high-resolution study designed for one primary purpose: finding an intracranial vascular abnormality. As a resident, mastering this read means being confident, systematic, and fast. When I was a fellow, the key was having a bulletproof search pattern for the high-yield locations. Let’s walk through the protocol, the template, and the key findings so you can dictate with confidence. For more guides like this, check out the residents and fellows resource hub.
2. What a CTA Head (Circle of Willis Only) Covers and What Attendings Look For
This is a targeted study. Unlike a full CTA Head and Neck, which is the workhorse for acute stroke to evaluate the arch-to-vertex circulation, the CTA Head (Circle of Willis only) is optimized for intracranial vascular pathology.
Your attending expects a clear, concise report that directly answers the clinical question. This study is primarily ordered to evaluate for:
- Intracranial aneurysm, especially as a source for a subarachnoid hemorrhage (SAH)
- Arteriovenous malformation (AVM) or dural arteriovenous fistula (dAVF)
- Intracranial vasospasm, typically as a complication 7-10 days after an SAH
- Distal branch occlusions (MCA, ACA, PCA) not well seen on non-contrast imaging
- Large-vessel intracranial vasculitis
The most common indications you’ll see are for acute SAH workup (paired with a non-contrast CT), suspected aneurysm, vasospasm surveillance, or pulsatile tinnitus. Your report should systematically address the patency and caliber of the major intracranial vessels and explicitly mention the common aneurysm locations.
3. Radiology Report Template for CTA Head (Circle of Willis Only)
Use this template as a starting point for your macros. It’s designed to be systematic, ensuring you don’t miss the critical “hot spots” where aneurysms love to hide.
Technique
Axial images were acquired from the skull base to the vertex following the administration of [50] mL of [Omnipaque 350] intravenous contrast. Bolus tracking was utilized. Multiplanar reformatted images, including maximum intensity projections (MIP) and 3D volume-rendered images, were reviewed.
Findings
Intracranial Arteries:
The visualized portions of the internal carotid arteries are patent.
Anterior Cerebral Arteries: The A1 and A2 segments are patent. The anterior communicating artery complex is unremarkable. No aneurysm is identified.
Middle Cerebral Arteries: The M1 and M2 segments are patent bilaterally. The MCA bifurcations are unremarkable. No aneurysm is identified.
Posterior Cerebral Arteries: The P1 and P2 segments are patent bilaterally. The posterior communicating arteries are unremarkable. No aneurysm is identified.
Vertebrobasilar System: The vertebral arteries and basilar artery are patent. The basilar tip is unremarkable. No aneurysm is identified.
Circle of Willis: [Describe any anatomic variants, e.g., fetal PCA, hypoplastic A1 segment].
Vessel Caliber: There is no evidence of focal stenosis, occlusion, or diffuse narrowing to suggest vasospasm.
Intracranial Veins:
The visualized dural venous sinuses, including the superior sagittal sinus and transverse sinuses, are patent.
Extravascular Findings:
Comparison is made to the prior non-contrast CT head from [Date]. No new or acute intracranial hemorrhage. No territorial infarct. The brain parenchyma is otherwise unremarkable. Visualized portions of the orbits, paranasal sinuses, and mastoid air cells are unremarkable.
Impression
- No evidence of intracranial aneurysm, vascular malformation, or significant stenosis.
- No evidence of large vessel occlusion.
4. Free Template Sources for Radiology Residents
Building a personal library of high-quality templates is one of the best things you can do during training. While the template above is a great starting point, two great free repositories exist that are worth bookmarking. These are maintained by major radiology organizations and offer a huge range of templates across all subspecialties.
- RadReport.org: Curated by the Radiological Society of North America (RSNA), this is a comprehensive library of peer-reviewed templates.
- Radiology Templates (AU): An excellent, well-organized library maintained by Australian radiologists with a practical, clinically focused approach.
5. The Next-Level Move: From Free-Form Dictation to Structured Reports
Templates are essential, but the real world of dictation is often a mix of structured reporting and free-form descriptions of positive findings. You might dictate “There is a 4 mm saccular aneurysm arising from the anterior communicating artery,” but then you have to manually slot that into the right section of your template and make sure the impression is perfect.
This is where AI-powered tools can streamline your workflow. Instead of just being a static text expander, modern reporting assistants can take your free-form dictation of positive findings and intelligently structure it. For example, GigHz Precision AI is designed to listen to your description of a finding and then generate a complete, structured report using pre-loaded templates from the American College of Radiology (ACR) and Society of Interventional Radiology (SIR). It helps ensure your final report is clean, consistent, and contains all the key elements your attending is looking for, without the manual copy-pasting.
6. When Should You Order a CTA Head (Circle of Willis Only)? ACR Appropriateness Criteria
Understanding when a study is indicated is just as important as reading it. The American College of Radiology (ACR) provides evidence-based guidelines through its Appropriateness Criteria. For indications related to intracranial vascular disease, the CTA Head is frequently a top choice.
According to the ACR’s topic on Cerebrovascular Diseases-Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage, a CTA of the head is “Usually Appropriate” for several common clinical scenarios.
For a patient with a known acute subarachnoid hemorrhage (SAH) seen on a non-contrast CT, a CTA is the recommended next study to identify a potential ruptured aneurysm. Similarly, for the initial imaging of suspected cerebral vasospasm or for surveillance of a known, untreated aneurysm, CTA is considered “Usually Appropriate.” The same rating applies to screening high-risk patients (e.g., those with a strong family history or certain genetic conditions) and for monitoring known high-flow vascular malformations like an AVM or dural AVF.
Key alternatives include MRA of the brain without contrast (using 3D Time-of-Flight sequences), which is a great option when IV contrast is contraindicated. For definitive evaluation and treatment planning, especially for aneurysms, catheter-based Digital Subtraction Angiography (DSA) remains the gold standard.
7. How Much Radiation Does a CTA Head (Circle of Willis Only) Deliver?
A common question from ordering providers and patients is about radiation dose. A CTA Head (Circle of Willis only) delivers an effective radiation dose of approximately 1-3 mSv.
To put that in perspective, this is in the low-dose tier of CT imaging (1-10 mSv) and is comparable to the amount of natural background radiation a person receives over several months to a few years. It’s a relatively small dose, especially when weighed against the clinical urgency of ruling out a life-threatening condition like a ruptured aneurysm. Modern CT scanners use automated dose modulation techniques to keep the dose as low as reasonably achievable while maintaining diagnostic image quality.
| Imaging Study | Typical Effective Dose |
|---|---|
| CTA Head (Circle of Willis) | 1-3 mSv |
| Natural Background Radiation (per year) | ~3 mSv |
| Chest X-ray (2 views) | ~0.1 mSv |
| CT Abdomen/Pelvis | ~10 mSv |
Dose estimates are based on curated data from ACR resources. Actual dose may vary based on patient size and specific scanner protocol.
8. CTA Head (Circle of Willis Only) Imaging Protocol — Phases, Contrast, and Reconstructions
A high-quality CTA depends on a precise protocol. The goal is to capture a pure arterial phase with dense opacification of the intracranial arteries and minimal venous contamination. This is achieved with a rapid contrast injection rate and bolus tracking.
The scan is a single helical acquisition from the skull base through the vertex. From this raw data, thin axial images are reconstructed, which are then used to generate the Maximum Intensity Projection (MIP) and 3D Volume Rendered (VRT) images that are essential for spotting small aneurysms.
| Parameter | Specification |
|---|---|
| Contrast | 50 mL of Iohexol/iopamidol (350-370 mgI/mL) at 5 mL/sec |
| Timing | Bolus tracking with ROI at the top of the aortic arch; threshold 120 HU + 5 sec delay |
| Coverage | Skull base to vertex |
| Helical Parameters | kVp: 100-120; Reference mAs: 200; Pitch: ~0.85 |
| Reconstructions | Thin axial (0.6-1.0 mm); 5 mm MIPs (axial, coronal, sagittal); 3D VRTs |
Common Protocol Pitfalls: The most common pitfall is related to contrast volume. While 50 mL is generally sufficient for a focused Circle of Willis study, if the clinical question requires evaluating the neck vessels as well, the contrast volume should be increased to 70-80 mL to ensure adequate opacification through the extended scan range.
9. The 3-Months-Free Offer for Radiology Residents and Fellows
3+ months free for radiology residents and fellows
If you want to look like a rockstar on your reports, we’ve got an offer for you. We’re giving trainees extended free access to GigHz Precision AI. You can dictate your positive findings in free form, and the AI will generate a clean, structured report using ACR and SIR templates, with the appropriate clinical decision support firing automatically.
All we ask in return is your feedback so we can keep improving the product for trainees on the front lines.
To apply, just let us know these three things:
- Your PGY year (e.g., PGY-2, PGY-4)
- Your training type (radiology residency or fellowship specialty)
- Your training program / hospital name
Signup is simple. No credit card, no long forms. Just reply to the application with those three items, and we’ll get you set up. You can apply for the residents free-access program here.
10. Frequently Asked Questions (FAQ)
Is GigHz Precision AI HIPAA-compliant?
Yes. The platform is designed for de-identified workflows by default and operates under a Business Associate Agreement (BAA) with covered entities. Patient confidentiality and data security are core to the system’s architecture.
Does this require a complex IT setup at my hospital?
No. GigHz Precision AI is a secure, browser-based tool. There is no software to install on hospital machines. It works on the computer in the reading room, your personal laptop, or even an iPad on call.
Can I use this alongside PowerScribe or other dictation systems?
Yes. Most residents use it in a “copy-paste” workflow. You dictate your findings into the tool, let the AI structure the report, review the output, and then paste the final, clean text into your hospital’s PACS/RIS.
Is it available on mobile or iPad?
Yes, the platform is web-based and responsive, so it works across desktops, laptops, and tablets like the iPad, which is perfect for checking things on the go or in the call room.
Can I customize the templates?
Yes. While the system comes pre-loaded with standard ACR and society-based templates, you can create, modify, and save your own templates to match your personal preferences or your institution’s specific formatting requirements.
What happens after I finish my residency or fellowship?
The free access program is specifically for trainees. After you graduate, you can transition to a standard plan for practicing radiologists. We offer discounts for recent graduates to help you get started in your new role.
Free GigHz Tools That Pair With This Article
Three free tools that complement the material above:
- ACR Appropriateness Criteria Lookup — Type an indication or clinical scenario in plain language and get the imaging studies the ACR rates for it, with adult and pediatric radiation levels. Built directly from 297 ACR topics, 1,336 clinical variants, and 15,823 procedure ratings.
- GigHz Imaging Protocol Library — A searchable library of 131 imaging protocols with the physics specs surfaced and the matching ACR Appropriateness Criteria alongside. Plain-English narratives readable in 60 seconds, organized by modality.
- GigHz Radiation Dose Calculator — Pick the imaging studies a patient has had and see total dose in millisieverts (mSv) with comparisons to natural background radiation, transatlantic flights, and chest X-rays. Useful for shared decision-making.
Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 7, 2026
