Quantitative Susceptibility Mapping as an Alternative to CT for Localizing Gold Intraprostatic Fiducial Markers

Gold fiducial markers (FMs) for prostate radiotherapy are commonly localized using Computed Tomography (CT), though interest in MR-only workflows is growing. One current limitation with magnitude-based MR-only workflows is the ability to distinguish FMs from blood products and calcifications because all appear as signal voids. Quantitative Susceptibility Mapping (QSM) separates sources based on their susceptibility, and may be a potential solution. We apply the QSMxT pipeline to gradient-echo images of a prostate cancer patient with FMs and a calcification. We found that QSM provided a contrast that could differentiate the FMs from calcifications to a degree comparable to CT.