Assessing image artifacts from radiotherapy electromagnetic transponders with metal-artifact reduction imaging

Image artifacts due to 14 gauge radiotherapy electromagnetic (EM) transponders were assessed on conventional spin echo images, and corrected using metal artifact reduction techniques: high bandwidth, view angle tilting (VAT), and slice encoding for metal artifact correction (SEMAC). Large areas of signal loss and/or pile-up were produced in an area extending up to 15.3 mm in radius for 14G transponders in standard imaging. Using high bandwidth imaging with VAT, in-plane artifact sizes were reduced by up to 35%. SEMAC did not significantly reduce in-plane or through plane artifact size for axially oriented images, but was effective in reducing through-plane artifacts for sagittal images. Using the experimental data, magnetic field maps were simulated so that the magnetic susceptibility of the transponder could be estimated and slice profiles could be visualized. Due to the large susceptibilities involved, current correction techniques are unable to fully correct artifacts due to EM transponders and significant areas of signal loss and distortion remain. Care should be taken when planning MRI following EM transponder implantation.