PET CT Artifact Troubleshooting Guide

Updated 13 November 2026 · Standard formula, shown below

This guide walks you through the most common PET/CT image artifacts—what causes them, how to recognize them, and the step-by-step fixes to prevent or correct them. You’ll learn practical techniques for patient preparation, acquisition, and reconstruction that directly improve image quality and diagnostic confidence. Before starting, ensure you have access to your scanner’s user manual, the raw sinogram data (for reprocessing), and the reconstruction software’s parameter settings.

What You’ll Need

Access to the PET/CT scanner’s acquisition and reconstruction console
Raw list-mode or sinogram data for reprocessing (if needed)
Patient preparation records (blood glucose, hydration, activity, scan delay)
CT attenuation correction maps and the original CT raw data
Quality control phantom and daily QC logs
Reconstruction software with adjustable parameters (matrix, filter, iterations, subsets)

Step-by-Step

Identify the artifact type. Visually inspect the images. Common categories: truncation (bright edges at body boundaries), metal artifacts (streaks from dental implants or prostheses), motion blur (respiratory or patient movement), attenuation correction mismatches (misregistration between CT and PET), and reconstruction artifacts (Gibbs ringing or excessive smoothing).
Check patient preparation. Review the blood glucose level (should be < 200 mg/dL for FDG), verify the patient fasted at least 4–6 hours, and confirm no recent vigorous exercise or caffeine intake. High glucose competes with FDG, causing diffuse background uptake that mimics a soft-tissue artifact.
Verify injection and uptake time. Confirm the injected activity and the exact uptake time (typically 60±10 minutes). If the uptake time is too short, blood-pool activity remains high, creating a generalized haze. If too long, lesion contrast may drop.
Assess patient motion. Review the CT and PET for misregistration. If the patient moved between CT and PET, the attenuation correction map will be misaligned, causing hot or cold bands at the edges of organs. Use the scanner’s motion correction software if available, or re-acquire the CT if the motion is severe.
Evaluate CT-based attenuation correction. Look for truncation artifacts—if the patient extends beyond the CT field of view, the PET emission data outside that FOV is not corrected, leading to false high uptake at the edges. Use extended FOV reconstruction or a dedicated truncation correction algorithm.
Handle metal artifacts. If the patient has dental fillings, hip prostheses, or other metal, the CT image will show bright streaks and dark bands. These propagate to the PET attenuation-corrected images as false uptake. Apply metal artifact reduction (MAR) software on the CT, or use a metal-aware reconstruction that segments the metal and recalculates attenuation.
Review reconstruction parameters. Check the matrix size (e.g., 128×128 vs 256×256) and filter settings. A too-small matrix or overly aggressive smoothing can blur small lesions, while a too-high filter cutoff can create Gibbs ringing (oscillating bright/dark rings around high-contrast edges). Adjust iterations and subsets: more iterations increase resolution but also noise; typical values are 2–4 iterations and 16–24 subsets for OSEM.
Check for random and scatter correction. Ensure that random coincidence correction and scatter correction are applied. If not, you’ll see a diffuse background that increases with activity. Verify the scatter fraction is within expected range (typically 30–40% for whole-body).
Inspect the CT itself. If the CT has beam-hardening artifacts (e.g., from dense contrast), they can cause false attenuation values. Use a lower kVp or a dedicated beam-hardening correction. Also check for incomplete breath-hold—if the CT is acquired at full inspiration and the PET at shallow breathing, the diaphragm position differs, causing a misregistration artifact.
Reprocess with corrected parameters. Once the cause is identified, reprocess the raw data with the appropriate correction. For example, if motion is the issue, use respiratory gating; if truncation, apply extended FOV; if metal, use MAR. Always compare the corrected images to the originals to confirm improvement.
Document and archive. Record the artifact type, cause, and correction applied. This helps in future scans and for quality assurance reviews.

Common Mistakes

Ignoring patient motion—even small movements can cause significant misregistration.
Using the CT from a different breathing phase without checking alignment.
Over-smoothing the reconstruction to reduce noise, which hides small lesions.
Not applying metal artifact reduction when metal is present.
Forgetting to update the attenuation map after a patient moves or after a CT injection.
Assuming all artifacts are from the PET—always check the CT first.

Tips

Always acquire the CT with the same breath-hold instructions as the PET (usually shallow breathing or end-expiration).
Use a dedicated QC phantom daily to catch reconstruction artifacts early.
For obese patients, consider increasing the CT tube current to reduce noise and truncation.
When in doubt, compare the non-attenuation-corrected PET images to the corrected ones—this helps distinguish true uptake from correction artifacts.
Keep a log of artifact types and causes; you’ll spot patterns and prevent them proactively.

Troubleshooting

If the artifact persists after following the steps:

Misregistration still visible? Re-acquire the CT with the patient in the exact same position. If that’s not possible, manually adjust the CT-to-PET registration in the reconstruction software.
Metal artifacts remain? Try a different MAR algorithm or use a lower-energy CT (e.g., 120 kVp instead of 140 kVp) if available. If the metal is extensive, consider a separate diagnostic CT with MAR.
Reconstruction artifacts? Try a different reconstruction algorithm (e.g., TOF if available) or increase matrix size. If Gibbs ringing persists, apply a mild post-filter.
If you cannot correct the artifact, note it in the report. The interpreting physician must know that a region may be falsely hot or cold.
If the artifact is in the CT itself (e.g., streak artifacts from patient motion), repeat the CT scan—it’s fast and low-dose.

Frequently Asked Questions

Why does my PET image show a bright rim around the body?

This is typically a truncation artifact—the patient extends beyond the CT field of view, so the attenuation correction is incomplete. Use an extended FOV reconstruction or a truncation correction algorithm.

Can dental fillings cause false FDG uptake in the brain?

Yes, metal artifacts from dental work can cause streaking on the CT, which propagates to the PET attenuation-corrected images, creating false uptake near the metal. Applying metal artifact reduction helps.

What is the best way to reduce respiratory motion artifacts?

Use respiratory gating during PET acquisition, or have the patient hold their breath during the CT (if possible) and breathe shallowly during PET. Also, ensure the CT and PET are acquired with the same breathing instructions.

Why does my image look blurry even with a high-resolution reconstruction?

Blur can be due to patient motion, a too-small matrix, or excessive smoothing. Check the raw data for motion, and try increasing the matrix size (e.g., from 128×128 to 256×256) without increasing smoothing.

How do I know if an artifact is from attenuation correction or from real uptake?

Compare the attenuation-corrected image to the non-attenuation-corrected image. If the area of concern disappears or changes dramatically, it’s likely a correction artifact.

What should I do if the artifact is only visible in one slice?

Check if the CT slice is misregistered with the PET slice. A slight misregistration can cause a focal artifact. Review the CT and PET fusion to confirm alignment.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.