A Computed Tomography (CT) scan uses specialized X-ray equipment and computer processing to create detailed cross-sectional images of the body. These images allow physicians to examine internal structures, organs, and tissues for signs of disease or injury with high precision. To ensure the clarity and diagnostic quality of these images, patients are typically instructed to remove all external items that could interfere with the X-ray beam. For this reason, you will generally be asked to remove your bra before a CT scan, particularly if the garment contains metallic components.
Why Metal Causes Image Distortion During CT Scans
A CT scanner works by rotating an X-ray source and detector array around the patient to collect data from multiple angles. When the high-energy X-ray beam encounters dense materials like metal, a physical process known as “beam hardening” occurs. This happens because the metal strongly absorbs the lower-energy X-ray photons, leaving a “harder,” higher-energy beam to pass through the remaining tissue.
This uneven absorption of X-rays leads to severe image distortion, which radiologists call “streaking artifacts.” These artifacts appear as dark bands between two high-density objects, often surrounded by bright streaks, radiating outward from the metallic source. Even a small piece of metal can create a large, disruptive streak that entirely obscures the surrounding anatomy.
The presence of these streaks can either hide a genuine medical issue or create a false appearance of a problem, significantly impacting the radiologist’s ability to interpret the scan accurately. This technical constraint is the primary reason why removing metal from the scan path is necessary for achieving a successful diagnostic examination.
Specific Garments and Accessories to Remove
The most common garment requiring removal is a traditional bra containing an underwire. The thin, dense metal wire is perfectly positioned to generate significant streaking artifacts across any scan focused on the chest, lungs, or upper abdomen. Because the wire is directly in the path of the X-ray beam, the resulting image distortion makes the underlying tissue impossible to evaluate.
Beyond the underwire, any bra containing metallic components should be removed, including metal hooks, clasps, or sliding adjusters on the straps. Even a small metal hook at the back can cause enough interference to blur a localized section of the image. This rule extends to athletic wear, such as sports bras or leggings, that may contain metal zippers, toggles on drawstrings, or decorative embellishments.
The necessity of removal is most pronounced when the CT scan is focused on the chest or upper abdomen, as the bra’s components are directly in the imaging field. However, the artifact streaks caused by metal can extend far from the object itself, potentially distorting images of the lower abdomen or even the pelvis.
Accessories
Accessories worn adjacent to the scan area must also be removed, as they pose the same risk of distortion. This includes necklaces, body piercings in the chest or sternum area, and hairpins or eyeglasses if the head or neck is being scanned. Patients should also check clothing for hidden metal, such as belt buckles, metal-studded pockets, or metallic thread woven into athletic wear.
What to Wear Instead and How to Prepare
To avoid image interference, the safest and most common practice is to change into a hospital-provided gown before the procedure. These garments are specifically designed to be entirely free of metal. If a gown is not required for your specific scan, you should wear comfortable, loose-fitting clothing that has absolutely no metal components.
Acceptable attire includes soft, non-metallic sports bras, drawstring pants, or a simple cotton t-shirt. It is important to meticulously confirm that the clothing is truly metal-free, checking for things like hidden metallic thread, decorative rivets, or small plastic zippers that may contain a metallic core. Patients should arrive early to allow ample time to change and to remove all accessories, such as watches, earrings, and glasses.
If you are uncertain about a particular item of clothing, communicate with the technologist before the scan begins. When in doubt, removing the item or opting for the hospital gown is the most reliable way to guarantee a clear, diagnostic-quality image.