[Medical Q&A] Why are we asked to take off clothes when taking X-rays?

Planner: Chinese Medical Association

Reviewer: Kong Lingyan, deputy chief physician, Peking Union Medical College Hospital

The principle of X-ray imaging is based on the fact that when X-rays penetrate different tissues of the human body, they produce different degrees of absorption and attenuation due to differences in tissue density, thus forming an image on the imaging plate or detector. Simply put, high-density tissue absorbs more X-rays and appears white on the film; low-density tissue absorbs less X-rays and appears black. The clothes we wear, especially clothing accessories containing metal, plastic and other materials, will seriously interfere with this imaging process.

Metal zippers, buttons, metal accessories, etc. on clothing have a much higher density than human tissue, and will show obvious high-density images on X-rays. These high-density images will overlap the body parts we need to observe. For example, when doing a chest X-ray, if there is a metal zipper on the clothes, it is likely to show a high-density image on the film, covering the lung tissue, making it difficult for doctors to accurately determine whether there is a disease in the lungs, and may even lead to misdiagnosis, causing unnecessary worries for patients and subsequent examinations and treatments.

In addition to metal objects, some thick clothing or clothing with prints or plastic decorations can also affect X-ray imaging. Although they do not cause strong interference like metal, they can also change the penetration and attenuation of X-rays to a certain extent, reduce the clarity of the image, and affect doctors' observation of subtle lesions.

Of course, when taking X-rays, doctors will also fully consider the privacy and comfort of patients. For patients with limited mobility or physical weakness, doctors will flexibly adjust the examination requirements according to the actual situation to minimize the inconvenience caused by undressing. At the same time, the hospital will also take corresponding measures to protect the privacy and dignity of patients.