How does metal affect the results of a pet scan?

Metals and Imaging: Pet scans rely on radioactive sugar honing to areas consuming lots of energy, like cancer (sarcoid too), metals from prior surgery usually doesn't interfere. Mri is a different story . Metal fragments, bullets, implanted devices can move or heat in magnetic fields. Modern medical implants (hips, knees, plates) commonly are compatible. They interefere with ct's and plane films: obstruct view.

Attenuation: The effect of metals on a pet scan are different than from the effects on cts or mris. Metals have a high atomic number which results in photoelectric absorption of the photons coming out from your body after a radiopharmaceutical injection for a pet study. The result is that those photons in the path of this metal will be attenuated, decreasing the counts on the image.

Usually not much: Metal can block the gamma rays that are emitted by the patient, and block the xrays from the ct portion of the pet/ct, which can create errors on one portion of the exam (called the attenuation corrected scan). However, the original pet data from the scan (uncorrected) is always available for review, so if the standard images have artifact on them, the uncorrected images can be reviewed.