A Realistic In Silico Brain Phantom for Quantifying Susceptibility Anisotropy‐Induced Error in Susceptibility Separation

Purpose To create a realistic in silico brain phantom for positive and negative magnetic susceptibility that incorporates susceptibility anisotropy, enabling the evaluation of how susceptibility anisotropy influences susceptibility separation algorithm performance. Methods We expanded an existing QSM validation phantom by creating separate maps for positive and negative susceptibility, with the option of modeling susceptibility anisotropy. Multi‐echo gradient echo data were simulated to evaluate four susceptibility separation techniques (‐separation, DECOMPOSE‐QSM, APART‐QSM, and ‐QSM). To assess the impact of noise, simulations were performed at different SNR levels (50, 100, 200, 300). Results Our findings showed that the error in negative susceptibility estimates increased by up to 53% when susceptibility anisotropy was present, compared to the case without susceptibility anisotropy, with ‐separation being the algorithm that was most sensitive to anisotropy. Robustness to noise varied across the assessed algorithms, with APART‐QSM and ‐separation having the highest and lowest sensitivity to noise, respectively. Conclusion The modified phantom is open‐source and can serve as a numerical ground truth for evaluating susceptibility separation methods. Our findings emphasize the importance of incorporating susceptibility anisotropy into susceptibility separation models to improve their accuracy.