Which CT artifact is commonly caused by metal implants?

Which CT artifact is commonly caused by metal implants?

• A. Ring artifact
• B. Motion artifact
• C. Beam-hardening streak artifact
• D. Partial volume averaging

Answer: (C)

Beam-hardening streak artifacts arise when dense metal implants alter the X-ray beam as it passes through the body. CT uses a polyenergetic beam, and metal absorbs lower-energy photons more readily. As the beam traverses the implant, the spectrum shifts toward higher energies, which the reconstruction can misinterpret, producing characteristic streaks and shading around the implant. Photon starvation—when so many photons are absorbed that very few reach the detectors—can worsen these streaks, making the area around the metal look streaked and low in signal. This combination is a well-known manifestation of how metal hardware affects CT images. Ring artifacts come from detector calibration or malfunction, not from the implant itself; motion artifacts result from patient movement during scanning; partial volume averaging arises from finite voxel size blending different tissues at interfaces.

Beam-hardening streak artifacts arise when dense metal implants alter the X-ray beam as it passes through the body. CT uses a polyenergetic beam, and metal absorbs lower-energy photons more readily. As the beam traverses the implant, the spectrum shifts toward higher energies, which the reconstruction can misinterpret, producing characteristic streaks and shading around the implant. Photon starvation—when so many photons are absorbed that very few reach the detectors—can worsen these streaks, making the area around the metal look streaked and low in signal. This combination is a well-known manifestation of how metal hardware affects CT images.

Ring artifacts come from detector calibration or malfunction, not from the implant itself; motion artifacts result from patient movement during scanning; partial volume averaging arises from finite voxel size blending different tissues at interfaces.