Cause of CT Image Artifacts

Examining the cause of CT artifacts, isolating ring artifact, streak artifact and steps you can take to prevent CT system down time.

Note: Perform axial test scans using water phantom for most consistent scan data. Helical scans may show partial ring or artifact that may increase troubleshooting difficulty.

Cause of CT Artifacts

Perform test scans using water phantom and examine the nature of the artifact. Artifact descriptors will help in isolating cause of CT artifacts.

Induced CT Artifact

Description: Typically represented as band artifacts or ring artifact with blurred edges. Contrast present on mylar window around the CT bore or beam obstruction during daily calibration can be cause for artifact.

How to remove contrast from CT mylar window

First, inspect mylar window for any small holes in the ring. Do not apply liquid solution if holes are visible in mylar window. Then, use warm water and rubbing alcohol solution on a clean cloth to wipe off any visible contrast along beam path. In this case, pour a small amount of solution on cloth and wipe with cloth to avoid excessive liquid. Avoid spilling any solution into CT gantry.

FInally, after contrast has been cleaned, perform daily calibration and test scans using quality assurance phantom.

Beam obstructions during daily calibrations cause image artifact. Additionally, CT daily QA scans may show elevated mean values. Water mean value only passes specification if value is within -3 to +3. Perform daily calibrations again after identifying and clearing beam obstruction.

CT Scanner Ring Artifact

Description: Clearly defined edges and usually localized to channel segmentation no more than 1mm in thickness. White or black in color. Ring artifacts occur as a result of data acquisition or detector issues. If experiencing ring artifacts during scanning try:

1) Choosing a different detector configuration ex. 4×5, 2×10, 8×2.5. Also try to choose different collimator setting by reducing detector coverage in an attempt to exclude bad channel during scan data acquisition.

2) If you cannot scan with a configuration that is free of ring artifacts or excludes bad data channel, you most likely have a Data Acquisition subsystem issue. Most causes of white ring artifact and dark ring artifact will likely be within the CT Gantry and will require a Field Engineer.

4 items to check before making a service call

CT Scan Room Temperature

First, check your scan room temperature. Ideal scan room temperature ranges from 68 degrees to 73 degrees Fahrenheit. Scanning should not be performed above 83 degrees F. Rising temperatures in scan room can overheat internal components and cause CT artifacts. Pause scanning until CT scan room temperature has normalized and is within recommended scanning temperature.

CT Gantry Exhaust Fan Functionality

Second, check CT gantry exhaust fans. Check the top of your CT gantry to make sure all fans are on. Heat buildup inside of the CT Gantry can cause damage to sensitive electrical components and power supplies. High gantry exhaust temperature relative to ambient temperature can be an indication that gantry cooling subsystem is not functioning properly.

Are fans not working? Check for radiant heat from gantry fan ports. Issues with power supplies or faulty fans can prevent heat from being evacuated from CT Gantry.

Power Down and Restart CT scanner

Last Resort: Power down entire system from A1 main disconnect power that is supplying power to CT system from facility; alternatively shut down gantry with gantry enable button on PDU. Leave system off for 10 minutes. Power back on using the green start button. Perform gantry reset by pushing the button with the blinking LED on the left or right gantry interface panels. This will remove all power from system and provide enough time for any stored voltage to bleed off. Restoring power to system resets all gantry subsystems and provides subsystem LED self tests. Boot system and perform test scans.

Contact MRI Repair Service Engineer (FE)

Call qualified Field Service Engineer for CT repair service. Contact us for a list of recommended service providers.

Cause of CT Artifacts: Conclusion

Most ring and band artifacts will require troubleshooting from a qualified field service engineer. While the cause of CT artifacts can vary, there are some simple steps that can be taken to ensure risk of induced artifact in calibration data is reduced to a minimum.

Additional items that will keep your system up and running: Changing HVAC or air conditioning filters regularly, regular planned maintenance, tracking daily quality control scans to ensure consistency and spot anomalies.

Additional Resources

• Top 5 Tips When Your CT is Not Scanning
• CT Scanner Price Guide
• Top 5 Tips to Reduce Downtime
• MRIPETCTSOURCE YouTube Channel

Does Your System Require On-site CT Scanner Repair Service? Contact Us Today!

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