MRA Brain Without Contrast (3D TOF) — Dictation, Appropriateness, and Dose for Residents

1. The MRA Brain Without Contrast: A Resident’s Guide to Aneurysm Hunting

It’s a routine outpatient MRA brain for aneurysm screening. The patient has a family history of subarachnoid hemorrhage, and your attending is meticulous about the circle of Willis. They expect you to comment on every major branch, rule out any saccular outpouching, and do it all without the crutch of contrast. You’re scrolling through the 3D time-of-flight (TOF) source images, knowing that a 2 mm anterior communicating artery aneurysm can easily hide in the overlap of a maximum intensity projection (MIP). The pressure isn’t about speed; it’s about precision.

When I was a junior resident, I’d spend half my time just trying to get the MIPs to look right, and the other half terrified I was missing a tiny bleb. The key, which an attending finally drilled into me, is a systematic approach to both the acquisition and the interpretation. This guide gives you that system, from protocol to dictation. For more guides and tools like this, check out the residents and fellows resource hub we’ve put together.

2. What an MRA Brain Without Contrast (3D Time-of-Flight) Covers and What Attendings Look For

A non-contrast MRA of the brain is the workhorse for non-invasive intracranial vascular screening. It leverages the principle of flow-related enhancement: fresh, unsaturated arterial blood flowing into the imaging slab appears bright against the background brain tissue, which has been saturated by radiofrequency pulses. A saturation band placed superiorly nulls the signal from incoming venous flow, isolating the arterial circulation.

This study is primarily designed to answer questions about vascular anatomy and major pathology. It is not the first choice for acute stroke, where CT angiography is much faster, or for detailed pre-operative planning, where digital subtraction angiography (DSA) remains the gold standard.

**Common Indications:**
* Screening for intracranial aneurysms in high-risk patients (e.g., family history, polycystic kidney disease)
* Follow-up of known, untreated aneurysms
* Workup of subarachnoid hemorrhage (SAH) when CTA is contraindicated
* Evaluation of suspected arteriovenous malformations (AVMs)
* Surveillance for vasospasm after SAH
* Workup for suspected Moyamoya disease

**What your attending expects in the report:**
* A clear statement on the technique (3D TOF without contrast).
* Systematic evaluation of the major intracranial arteries: internal carotid arteries (cavernous, supraclinoid segments), anterior cerebral arteries (A1, A2 segments), middle cerebral arteries (M1, M2 segments), vertebral arteries, basilar artery, and posterior cerebral arteries (P1, P2 segments).
* Specific mention of common aneurysm locations: anterior communicating artery, posterior communicating arteries, MCA bifurcation, and basilar tip.
* A definitive statement on the presence or absence of aneurysms, AVMs, stenosis, or occlusion.
* Measurement of any aneurysm found (neck, maximal dimensions) and description of its morphology.

3. Radiology Report Template for MRA Brain Without Contrast (3D Time-of-Flight)

This template provides a solid starting point for your dictations. Remember to always review the source images first, as small aneurysms can be completely obscured on MIP reconstructions.

Technique

Magnetic resonance angiography of the intracranial arteries was performed without intravenous contrast using a 3D time-of-flight (TOF) technique. Multiplanar reformatted images, including maximum intensity projections (MIPs), were reviewed.

Findings

VESSELS:

Anterior Circulation:
Internal Carotid Arteries: The cavernous and supraclinoid segments of the internal carotid arteries are patent and normal in caliber. No significant stenosis, occlusion, or aneurysm is identified.
Anterior Cerebral Arteries: The A1 segments are symmetric. The A2 segments are unremarkable. The anterior communicating artery is unremarkable.
Middle Cerebral Arteries: The M1 and M2 segments are patent bilaterally without evidence of stenosis, occlusion, or aneurysm.

Posterior Circulation:
Vertebral Arteries: The intracranial vertebral arteries are patent and converge to form the basilar artery. [Comment on dominance if relevant, e.g., The left vertebral artery is dominant.]
Basilar Artery: The basilar artery is patent and normal in caliber through its course to the tip.
Posterior Cerebral Arteries: The P1 and P2 segments are patent bilaterally.

Circle of Willis: [Describe any variants, e.g., Fetal origin of the right posterior cerebral artery. The posterior communicating arteries are symmetric and patent.]

Other Findings: No evidence of arteriovenous malformation, fistula, or other vascular anomaly is seen. The visualized major dural venous sinuses are patent.

Impression

1. No evidence of intracranial aneurysm, arteriovenous malformation, significant stenosis, or occlusion.

2. Normal appearance of the major intracranial arteries.

4. Free Radiology Template Sources

Building a personal library of high-quality templates is a rite of passage in residency. Before you build your own from scratch, know that two great free repositories exist, curated by radiologists for radiologists. They are excellent starting points for common and uncommon studies alike.

• RadReport.org: Maintained by the Radiological Society of North America (RSNA), this is a comprehensive library of peer-reviewed templates covering nearly every modality and subspecialty.
• Radiology Templates (AU): An excellent, straightforward resource maintained by Australian radiologists with clean, practical templates that are easy to adapt.

5. The Next-Level Move: Free-Form Dictation to Structured Report

Templates are great, but they can feel rigid, especially when you have multiple positive findings. The workflow most of us want is to simply dictate the findings as we see them—”3 mm saccular aneurysm at the ACom,” “moderate stenosis of the left M1 segment”—and have the software handle the rest.

This is the core idea behind GigHz Precision AI. It’s designed to take your free-form dictation of positive findings and intelligently generate a complete, structured report. The system uses pre-loaded templates from governing bodies like the American College of Radiology (ACR) and Society of Interventional Radiology (SIR) to ensure your output is clean, consistent, and contains the key elements your attending is looking for. It helps streamline the reporting process, letting you focus on the diagnostic task rather than on formatting.

6. When Should You Order an MRA Brain Without Contrast? ACR Appropriateness Criteria

Knowing when an MRA Brain is the right call is just as important as reading it correctly. The American College of Radiology (ACR) provides evidence-based guidelines for common clinical scenarios. For cerebrovascular imaging, the key documents are “Cerebrovascular Diseases-Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage” and “Cerebrovascular Disease.”

Here’s how non-contrast MRA fits in:

• High-risk cerebral aneurysm screening: For patients with a strong family history or conditions like polycystic kidney disease, non-contrast MRA is rated as Usually Appropriate by the ACR. It provides excellent detection for aneurysms ≥3 mm without radiation or contrast.
• Known cerebral aneurysm surveillance (untreated or previously treated): For monitoring known aneurysms, MRA without contrast is also Usually Appropriate. It is the preferred modality for serial follow-up.
• Known acute subarachnoid hemorrhage (SAH) on CT: When trying to find the source of a bleed, CTA is typically the first choice. However, if iodinated contrast is contraindicated (e.g., severe renal failure, allergy), MRA without contrast May Be Appropriate, though it is less sensitive than CTA or DSA for small aneurysms.
• Suspected stroke (less than 6 hours): In the hyperacute setting, time is critical. CTA is Usually Appropriate and much faster. MRA without contrast May Be Appropriate as part of a comprehensive MRI stroke protocol but is not the first-line vascular imaging choice.
• Suspected central nervous system (CNS) vasculitis: For initial imaging of suspected vasculitis, MRA without contrast is considered Usually Appropriate, often performed alongside conventional brain MRI sequences to look for associated parenchymal changes.

Key alternatives include CTA of the head, which is faster and better for small aneurysms but requires radiation and iodinated contrast; contrast-enhanced MRA (CE-MRA), which can improve visualization of slow-flow states or distal vessels; and catheter-based Digital Subtraction Angiography (DSA), the invasive gold standard reserved for problem-solving and treatment.

7. MRA Brain Without Contrast Imaging Protocol — Technique and Parameters

A high-quality 3D TOF MRA depends on getting the technical parameters right. Motion is the enemy, as it degrades the 3D acquisition significantly. The goal is to achieve high spatial resolution to detect small vessels and aneurysms while maintaining a good signal-to-noise ratio (SNR). 3T scanners are generally preferred over 1.5T for their superior SNR.

The protocol is centered on a single, high-resolution 3D acquisition covering the circle of Willis.

Common Protocol Pitfalls:

• Flow-related artifacts: Slow or turbulent flow (e.g., in a large aneurysm or distal to a stenosis) can cause signal loss, mimicking a stenosis. If there’s clinical suspicion, a phase-contrast MRA or contrast-enhanced MRA may be needed for confirmation.
• Venous contamination: If the superior saturation band is misplaced or fails, bright signal from venous structures can overlap and obscure arteries, particularly around the cavernous sinus.
• Relying only on MIPs: This is the classic resident mistake. Maximum intensity projections are great for a quick overview but can hide small aneurysms due to vessel overlap. Always scroll through the thin-slice source data.

8. The 3-Months-Free Offer for Residents and Fellows

We’re offering 3+ months of free access to GigHz Precision AI for all radiology residents and fellows. The goal is to help you look like a rockstar on your reports. You can dictate your positive findings in free form, and the AI will generate a clean, structured report using ACR and SIR templates, firing the appropriate clinical decision support automatically.

All we ask in return is your feedback so we can keep improving the product for trainees.

The signup is simple. No credit card, no long forms. To get started, just provide these three items:

1. Your PGY year (e.g., PGY-2, PGY-4)
2. Your training type (radiology residency or fellowship specialty)
3. Your training program / hospital name

Ready to give it a try? Apply for the residents free-access program here.

9. Frequently Asked Questions (FAQ)

Is GigHz Precision AI HIPAA-compliant?

Yes. The platform is designed for de-identified workflows by default. It operates on the anonymized text of your findings, not on patient-identifiable images or demographics from the PACS. No PHI is required to use the tool.

Do I need my hospital’s IT department to set this up?

No. GigHz Precision AI is browser-based and requires no local software installation or integration with your EMR or PACS. It works on any modern web browser, including the one on your call-room computer or personal iPad.

How does this work with PowerScribe or other dictation systems?

It works alongside your existing system. You dictate your findings as you normally would. You can then use the AI-generated structured text to quickly build your final report in PowerScribe, Fluency, or whatever system your institution uses, ensuring it’s complete and well-formatted.

Can I use this on my phone or iPad?

Yes, the platform is fully responsive and works on mobile devices and tablets. This is particularly useful for reviewing templates or checking criteria on the go.

Can I customize the report templates?

Yes. While the system comes pre-loaded with standard ACR and society-based templates, you can create, modify, and save your own custom templates to match your personal style or your institution’s specific requirements.

What happens after my residency or fellowship ends?

We have straightforward continuity plans for graduating trainees who want to continue using the platform in their practice. Your custom templates and preferences are saved to your account.

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