CT Colonography (Virtual Colonoscopy) — Dictation, Appropriateness, and Dose for Residents

1. The Attending-Ready CT Colonography Read

The request comes in from GI: a 72-year-old on Eliquis had an incomplete optical colonoscopy due to a tortuous sigmoid. They couldn’t clear the transverse or ascending colon, and they need you to finish the job. Your attending expects a clean, structured report with a C-RADS classification for any polyps and an E-RADS score for the inevitable extracolonic findings. You need to be systematic, confident, and fast.

When I was a fellow, the 3D fly-through felt like a video game, but the real work is in the 2D multiplanar reconstructions (MPRs), meticulously comparing the supine and prone images to differentiate a mobile piece of tagged stool from a fixed, flat lesion. Getting this right means knowing the protocol, the reporting framework, and what to look for before you even open the case. We built this guide—and our entire residents and fellows resource hub—to help you nail these reads every time.

2. What a CT Colonography (Virtual Colonoscopy) Covers and What Attendings Look For

CT Colonography (CTC), or virtual colonoscopy, is a low-dose CT technique designed specifically for evaluating the gas-distended colon. It’s not a general-purpose belly CT; it’s a dedicated screening and diagnostic tool. The key is meticulous bowel prep with fecal tagging (oral contrast to make residual stool bright) and colonic insufflation with CO2.

This study is primarily designed to answer:

• Is there evidence of colorectal polyps, particularly those ≥6 mm? (Sensitivity is around 90% for polyps ≥10 mm).
• Is there a mass concerning for colorectal cancer?
• Can we evaluate the proximal colon that was inaccessible during an incomplete optical colonoscopy?
• Are there any clinically significant extracolonic findings (e.g., aortic aneurysm, renal mass, lung nodule)? These are found in about 10-15% of screening CTCs.

Your attending will expect a report that systematically evaluates the entire colon, from rectum to cecum, and explicitly states the C-RADS (CT Colonography Reporting and Data System) category. They’ll also want a clear summary of any significant extracolonic findings, categorized using E-RADS.

3. Radiology Report Template for CT Colonography (Virtual Colonoscopy)

Use this template as a starting point for your macros. The key is to be systematic and to use the C-RADS/E-RADS framework in your impression to provide clear, actionable recommendations.

Technique

Low-dose CT of the abdomen and pelvis was performed without intravenous contrast following colonic insufflation with carbon dioxide. Helical images were acquired in both supine and prone positions. Multiplanar 2D reformations and 3D endoluminal “fly-through” images were reviewed on a dedicated workstation.

Bowel preparation and distention: [Adequate/Suboptimal/Inadequate].
Fecal and fluid tagging: [Adequate/Suboptimal/Inadequate].

Findings

COLON: The colon is well-distended and cleansed. No suspicious wall thickening, mass, or stricture is identified. Evaluation for polyps reveals:

• Rectum: No polyps identified.
• Sigmoid Colon: No polyps identified.
• Descending Colon: No polyps identified.
• Transverse Colon: [Describe any polyps: e.g., “A 7 mm sessile polyp is seen along the anti-mesenteric border of the mid transverse colon, fixed in location on supine and prone imaging.”]
• Ascending Colon: No polyps identified.
• Cecum: No polyps identified.

Appendix: Visualized and unremarkable.
Diverticulosis: [Present/Absent]. If present, describe location and any signs of active inflammation.

EXTRACOLONIC FINDINGS: Systematic review of the extracolonic structures reveals:

• Liver: No suspicious lesion.
• Gallbladder and Biliary Tree: Unremarkable.
• Spleen, Pancreas, Adrenal Glands: Unremarkable.
• Kidneys and Ureters: [e.g., “Simple 2 cm cyst in the right kidney, upper pole.”]
• Aorta and IVC: No aneurysm or significant adenopathy.
• Bones: No aggressive osseous lesion.
• Visualized Lung Bases: [e.g., “A 5 mm non-calcified nodule in the right lower lobe.”]

Impression

1. [C-RADS Category and description]. For example: “C-RADS C2: One 7 mm polyp in the transverse colon. Surveillance CT colonography in 3 years is recommended per guidelines.” or “C-RADS C3: 12 mm pedunculated polyp in the sigmoid colon. Referral for optical colonoscopy and polypectomy is recommended.”

2. [E-RADS Category and description of extracolonic findings]. For example: “E-RADS E2: Simple right renal cyst, clinically unimportant.” or “E-RADS E4: 5 mm non-calcified pulmonary nodule in the right lower lobe, potentially important. Recommend follow-up per Fleischner Society guidelines.”

3. [Other findings, e.g., “Mild sigmoid diverticulosis without evidence of diverticulitis.”]

Key Principles for the Impression:

• C-RADS is mandatory: C0 (inadequate), C1 (normal), C2 (small polyp 6-9 mm), C3 (≥10 mm polyp or 3+ medium polyps), C4 (mass concerning for cancer).
• E-RADS for everything else: E1 (normal), E2 (unimportant), E3 (likely unimportant), E4 (potentially important).
• Compare Supine and Prone: Your confidence in a fixed lesion skyrockets when you confirm its location on both scans. Mention this if relevant.

4. Free Radiology Template Sources

Building a personal macro library is a rite of passage. If you’re looking for more templates to adapt, two great free repositories exist. They are maintained by radiologists for radiologists and offer a solid starting point for a wide range of studies.

• RadReport.org: Curated by the RSNA, this is one of the most comprehensive and widely used free template libraries available.
• Radiology Templates (AU): An excellent, well-organized library maintained by Australian radiologists with a practical, clean layout.

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

The real bottleneck on call isn’t dictating the findings; it’s formatting them into the perfect, attending-approved structure with all the right scoring systems and follow-up recommendations. This is where AI-powered tools can streamline your workflow. Instead of clicking through a complex macro, you can dictate the positive findings in free form—”seven millimeter sessile polyp in the transverse colon, five millimeter lung nodule right lower lobe”—and let the software do the rest.

GigHz Precision AI is designed for this exact task. It parses your free-form dictation of findings, generates a fully structured report using pre-loaded ACR and society-backed templates, and helps ensure that classifications like C-RADS and E-RADS are correctly applied in the impression. It’s about getting the clerical work out of the way so you can focus on the diagnostic interpretation.

6a. When Should You Order a CT Colonography? ACR Appropriateness Criteria

The decision to order a CTC is guided by established clinical criteria, primarily for colorectal cancer (CRC) screening. The American College of Radiology (ACR) provides clear guidance on this topic.

According to the ACR Appropriateness Criteria for Colorectal Cancer Screening, CT Colonography is rated as Usually Appropriate for average-risk individuals as an alternative to optical colonoscopy. It’s also a primary tool for completing a colorectal evaluation after an incomplete optical colonoscopy, a very common real-world indication.

Key alternatives for CRC screening include:

• Optical Colonoscopy: The gold standard, as it allows for direct visualization, biopsy, and polypectomy in a single session.
• Stool DNA Testing (e.g., Cologuard): A non-invasive option that detects abnormal DNA and blood in the stool. Positive tests require a follow-up colonoscopy.
• Fecal Immunochemical Test (FIT): An annual test that detects human blood in the stool, also requiring colonoscopy for positive results.

CTC is generally not the first choice for evaluating acute symptoms like a GI bleed or colitis, where standard contrast-enhanced CT or endoscopy are preferred.

6b. How Much Radiation Does a CT Colonography Deliver?

Since CTC is often used for screening, radiation dose is a critical consideration. The protocol is specifically designed to be “low-dose.”

The estimated effective dose for a complete two-position (supine and prone) CT Colonography is approximately 4-8 mSv. This places it in the low-to-moderate radiation exposure tier, comparable to a few years of natural background radiation. The use of automated exposure control and iterative reconstruction techniques helps keep the dose as low as reasonably achievable while maintaining diagnostic image quality for polyp detection.

This dose is significantly lower than a standard diagnostic or staging CT of the abdomen and pelvis, reflecting its dedicated role in screening and polyp detection where high-contrast resolution is less critical than spatial resolution.

6c. CT Colonography (Virtual Colonoscopy) Imaging Protocol — Phases, Contrast, and Reconstructions

A successful CTC relies on a highly standardized protocol focused on optimal colonic distention and low-dose acquisition. Unlike many abdominal CTs, intravenous contrast is not routinely used unless the study is being performed for cancer staging in a patient with a known obstructing lesion.

The core of the protocol is acquiring thin-slice helical data in two patient positions to differentiate fixed polyps from mobile stool and fluid. CO2 is preferred for insufflation because it is absorbed much more quickly than room air, leading to less patient discomfort after the procedure.

Common protocol pitfalls:

• Inadequate Insufflation: Collapsed segments of the colon are uninterpretable and can hide significant pathology. This is a common reason for a C-RADS C0 (inadequate) study.
• Poor Bowel Prep/Tagging: Large amounts of untagged residual stool can obscure the colonic mucosa and mimic polyps, leading to false positives or non-diagnostic studies.
• Skipping the Second Position: The prone or decubitus scan is not optional. It is essential for confirming that a potential polyp is a true, fixed lesion rather than mobile debris.

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

3+ months free for radiology residents and fellows

Look like a rockstar on your reports—dictate positive findings in free form, and our AI generates a structured report using ACR and SIR templates with the appropriate clinical decision support firing automatically. This is your chance to try the reporting workflow of the future, today.

All we ask is 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 specific fellowship)
3. Your training program / hospital name

Ready to give it a try? Send us your details and apply for the residents free-access program.

8. Frequently Asked Questions

Is GigHz Precision AI HIPAA-compliant?

Yes. The platform is designed for de-identified workflows by default. You dictate findings, not raw PHI. It operates securely within compliance frameworks to protect data privacy.

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 IT approval. It works on any modern computer, including the call-room PC or your personal laptop/iPad.

How does this work with PowerScribe or other dictation systems?

It works alongside your existing PACS and dictation system. You can dictate your findings into the GigHz web interface, and the AI generates a structured report. You then copy and paste the final, formatted text into your official reporting system. This ensures the final report is clean, structured, and complete.

Can I customize the templates?

Yes. While the system comes pre-loaded with ACR, LI-RADS, C-RADS, and other society-standard templates, you can create and save your own customized versions to match your personal or institutional preferences.

What happens after my residency or fellowship ends?

We offer continuity plans for graduating residents and fellows who want to continue using the platform in their practice. Your templates and customizations can be carried over, providing a consistent workflow as you transition to being an attending.