It sounds like you're referring to the need to remove or cover metal items before undergoing a CT (CAT) scan. Indeed, many metals can interfere with imaging, so patients are often advised to remove items like zippers, jewelry, belts, or other metallic accessories before the scan.
Zippers on clothing can typically be covered with a shirt or other fabric if removal isn't possible, but it's always best to inform the radiology staff of any metal on your clothing. They can advise you on what to do to ensure the imaging is clear and accurate. Always follow the specific instructions provided by your healthcare provider or the facility conducting the scan.