Guidelines for QSM phantom production and evaluation of candidate phantom materials

Purpose: Quantitative susceptibility mapping (QSM) is an MR technique that depicts and precisely quantifies spatial biodistributions from hypointense blooming artifacts. Recently, QSM has gained much uptake as method for mapping iron and identifying calcium. However, QSM is missing a truth for each of these materials. Guidelines for reproducible workflows for QSM phantom design and production need to be developed to accelerate standardization efforts. This manuscript details a rigorous protocol for QSM phantom design and production, then provides recommendations for iron- and calcium-based materials given the inter-session repeatability and inter-scanner reproducibility of their QSM measurements. Methods: 5 concentrations of 4 materials were imaged with a multi-echo gradient-echo acquisition at 3 and 7 Tesla. The intra-session, inter-session repeatability, inter-scanner reproducibility and molar susceptibility by QSM were quantified. Results: The QSM measurements of USPIO had a moderate to good inter-session repeatability. The molar susceptibility was approximately 2.45 times larger at 3 T compared to 7 T. The QSM measurements of ferritin had excellent inter-session repeatability. The molar susceptibility was approximately 4 \% larger at 3 T compared to 7 T. The QSM measurements of calcium chloride had excellent inter-session repeatability and excellent inter-scanner reproducibility. The QSM measurements of calcium carbonate had a good to excellent inter-session repeatability and an excellent inter-scanner reproducibility. Conclusion: This work reveals ferritin and calcium chloride to be the most repeatable and reproducible iron-and calcium-based materials for QSM, respectively. A detailed methodology for phantom production, concentration ranges, visual analysis and statistical analysis are provided. ### Competing Interest Statement Kieran OBrien and Jin Jin are employees of Siemens Healthineers in Australia. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a conflict of interest.