A Computed Tomography (CT) scan is a diagnostic imaging tool that uses X-rays and computer processing to create detailed, cross-sectional images of the body. The CT system measures how different tissues absorb the radiation beam.
The general rule for this procedure is that any metal objects near the area being scanned should be removed. Metallic jewelry and accessories interfere with the image acquisition process, potentially compromising the scan’s diagnostic quality. Removing such items helps ensure the most accurate results for the radiologist, as the interference relates to image clarity, not patient safety.
Understanding Image Artifacts in CT Scans
The reason metal must be removed relates to how the dense material interacts with the X-ray beam, leading to image artifacts. An artifact is a distortion, streak, or shadow on the resulting image that does not correspond to the patient’s actual anatomy.
Metal is so dense that it effectively stops the X-ray photons, causing the imaging computer to receive incomplete or inaccurate data. This results in bright and dark streaks radiating outward from the metal object.
These streaks can obscure the soft tissues and pathology the physician is trying to evaluate. For instance, a small tumor or an internal injury could be completely hidden by the artifact created by a nearby accessory.
Artifacts do not pose a physical risk to the patient, but they can lead to a non-diagnostic scan, meaning the procedure may need to be repeated. High atomic number metals, such as iron or platinum, tend to produce more pronounced artifacts. Modern CT scanners employ advanced techniques, but these programs cannot always completely eliminate the distortion, especially when the metal is within the main field of view.
Practical Guide to Removing Jewelry
To ensure the best possible image quality, patients must remove all metallic items close to the region of interest being scanned. This includes common items such as necklaces, watches, bracelets, and rings, even if they are made of precious metals like gold or silver. Earrings and other facial piercings are particularly problematic for head and neck scans and must be removed prior to the procedure.
For scans of the chest or abdomen, accessories like underwire bras, metallic belt buckles, and body piercings must be taken out. Metal hairpins, barrettes, and clips will cause severe streaking on head and brain scans. Removable dental work, including dentures or retainers with metal components, should also be taken out if the scan involves the head or jaw.
While items far away from the scan area might not directly affect the images, many facilities prefer the removal of all personal jewelry. Patients should secure valuables before arriving for the appointment. If an item cannot be easily removed, the patient must communicate this to the technologist before the scan begins.
Handling Non-Removable Metal and Internal Implants
A separate category exists for metal that cannot be easily or safely removed, such as internal medical devices or permanent body modifications. Patients must inform the technologist about any surgical implants, which include joint replacements, plates, screws, surgical clips, stents, and pacemakers. Permanent piercings, like dermal anchors or specific facial jewelry requiring a tool for removal, also fall into this category.
These internal metal objects will still create artifacts, but their presence is necessary for the patient’s condition. In these cases, the technologist can employ specialized techniques to minimize image degradation. Modern CT units often have Metal Artifact Reduction (MAR) software, which uses complex algorithms to digitally correct the streaking caused by the metal.
The technologist may also adjust the scan parameters, such as increasing the kilovoltage or altering the scan angle, to reduce the severity of the artifacts. For example, if a hip replacement is present, the scan protocol for the pelvis might be modified to better visualize the surrounding soft tissues. While these methods cannot always produce a perfectly clear image around the implant, they significantly improve the diagnostic quality compared to an uncorrected scan.