Examining the cause of CT artifacts, isolating ring artifact, streak artifact and steps you can take to prevent CT system down time.
Ring artifacts in CT scans are circular or ring-like image distortions characterized by black or white edges that can degrade the diagnostic quality of images and can lead to misinterpretation or misdiagnosis.
These image distortions are produced when one or more detector channels generate spikes or dips in the scan data. A ring artifact appears in images when image data in one or more detector channels registers outside of the system’s tolerance levels. The most common causes of ring artifacts in CT scans are faulty detector components, noisy power supplies, calibration errors, obstructions in the X-ray beam, or even physical damage to detector modules. Read more below.
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.
Perform test scans using water phantom and examine the nature of the artifact. Artifact descriptors will help in isolating cause of CT artifacts.
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.
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.
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.
To resolve ring artifacts, troubleshooting and corrective action is required. This may involve removing obstructions in the path of the X-ray beam or replacing faulty detector components. After performing corrective action, the system will need to be recalibrated In order to resolve the CT ring artifact.
It is important to note that performing calibrations before addressing the underlying issue can mask the appearance of the ring artifact but will complicate troubleshooting the root cause.
To effectively resolve a CT scan ring artifact, it is advisable to conduct a thorough examination of the patient database to identify when the artifact first appeared and track the frequency of occurrence.
Once this information is obtained, promptly notifying the CT scan service provider with these details would be the recommended course of action. By doing so, the service provider can be informed of the artifact’s history and take appropriate measures to resolve the ring artifact effectively.
If you are currently experiencing a CT scan ring artifact, here’s a few things to know:
Ring artifacts in CT scans may not appear on every image and often occur only with specific scan parameters selected.
When ring artifacts are first noticed, it’s useful to run test scans with DQA phantoms to assess your system’s limitations.
Perform multiple test series, adjusting different scan parameters. Start by switching the focal point: if you’re using a large focal point, switch to a small one, or vice versa. Next, adjust detector configuration settings, such as slice thickness and images per rotation. You may find that only certain protocols are affected, or that all of them are. However, this quick 5-minute evaluation is invaluable for assessing current scan limitations and determining which patients can still be scanned without concerns about ring artifacts.
To learn more about CT scan ring artifacts, check out some of the helpful resources listed below.
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.
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.
Call qualified Field Service Engineer for CT repair service. Contact us for a list of recommended service providers.
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.
Does Your System Require On-site CT Scanner Repair Service? Contact Us Today!
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CT scan ring artifact explained. CT scan machine pictured left, CT ring artifact example pictured right.
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