What Happens If You X-Ray Metal?

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What Happens If You X-Ray Metal
Metal absorbs x-rays, so it blocks the view of underlying tissue. Also, it can create ghost images that make the image harder to read.
X-ray of Metal Ring and Hand by Röntgen of Albert von Kölliker's
Röntgen’s first x-ray of a person was his wife’s hand (1895), which had a ring. He later took this x-ray of Albert von Kölliker’s hand.

Before you get an x-ray, mammogram, CT scan, or fluoroscopy, the doctor advises you to remove eye glasses, jewelry, and other metal objects. So, you may wonder what happens when you x-ray metal.

Appearance of Metal on an X-Ray

Metal appears as a light area on an x-ray (or a dark area on the image’s negative). This is because, like bone and dental enamel, metal is dense and absorbs x-radiation. However, metal also scatters some radiation and releases photons when x-rays interact with electrons in the metal atoms. This produces phantom images that make other parts of the image harder to see.

Reason to Remove Metal for X-Rays

The reason you’re asked to remove metal before an x-ray is because the bright spots obscure underlying structures, while the ghost images mar the image. The end result is that the radiologist may need to take additional scans to get the best angle. Minimizing the number of pictures means reducing the amount of absorbed radiation. This is important because x-rays can cause developmental defects and cancer.

The absorbed energy also heats up metal. This isn’t an issue with an x-ray or mammogram, but becomes a consideration with longer scans like fluoroscopy.

Is Metal Dangerous With X-Rays?

Obviously, it’s not always possible to remove metal. People with implants can’t move them. X-rays don’t harm implants and the interaction between metal and the radiation doesn’t damage equipment providing the metal object isn’t directly between the collimator and image receptor.

However, metal objects are an issue with MRI equipment. Some metal objects are attracted to the powerful magnetic field and can become projectiles in the MRI room. Fortunately, most metal implants, like joint replacements and pins connected to bone, won’t move. Some magnetic metals, like pacemaker wires, may react to the magnetic field. Some patients feel heat or vibration at the site of the implant. Finally, metal implants may significantly distort MRI imaging.

References

  • Hall E.J.; Brenner, D.J. (2008). “Cancer risks from diagnostic radiology”. Br J Radiol. 81 (965): 362–78. doi:10.1259/bjr/01948454
  • Herman, Gabor T. (2009). Fundamentals of Computerized Tomography: Image Reconstruction from Projections (2nd ed.). Springer. ISBN 978-1-85233-617-2.
  • Roobottom, C.A.; Mitchell, G.; Morgan-Hughes, G. (2010). “Radiation-reduction strategies in cardiac computed tomographic angiography”. Clin Radiol. 65 (11): 859–67. doi:10.1016/j.crad.2010.04.021
  • Stanton, Arthur (1896). “Wilhelm Conrad Röntgen On a New Kind of Rays: translation of a paper read before the Würzburg Physical and Medical Society, 1895”. Nature. 53 (1369): 274–6. doi:10.1038/053274b0