Design and evaluation of quantitative MRI phantoms to mimic the simultaneous presence of fat, iron, and fibrosis in the liver.

Purpose: To design, construct, and evaluate quantitative MR phantoms that mimic MRI signals from the liver with simultaneous control of three parameters: proton-density fat fraction (PDFF), R 2 ∗ , and T ₁ . These parameters are established biomarkers of hepatic steatosis, iron overload, and fibrosis/inflammation, respectively, which can occur simultaneously in the liver.
Methods: Phantoms including multiple vials were constructed. Peanut oil was used to modulate PDFF, MnCl ₂ and iron microspheres were used to modulate R 2 ∗ , and NiCl ₂ was used to modulate the T ₁ of water (T _1,water ). Phantoms were evaluated at both 1.5 T and 3 T using stimulated-echo acquisition-mode MRS and chemical shift-encoded MRI. Stimulated-echo acquisition-mode MRS data were processed to estimate T _1,water , T _1,fat , R 2 , water ∗ , and R 2 , fat ∗ for each vial. Chemical shift-encoded MRI data were processed to generate PDFF and R 2 ∗ maps, and measurements were obtained in each vial. Measurements were evaluated using linear regression and Bland-Altman analysis.
Results: High-quality PDFF and R 2 ∗ maps were obtained with homogeneous values throughout each vial. High correlation was observed between imaging PDFF with target PDFF (slope = 0.94-0.97, R ² = 0.994-0.997) and imaging R 2 ∗ with target R 2 ∗ (slope = 0.84-0.88, R ² = 0.935-0.943) at both 1.5 T and 3 T. The values of R 2 , fat ∗ and R 2 , water ∗ were highly correlated with slope close to 1.0 at both 1.5 T (slope = 0.90, R ² = 0.988) and 3 T (slope = 0.99, R ² = 0.959), similar to the behavior observed in vivo. The value of T _1,water (500-1200 ms) was controlled with varying NiCl ₂ concentration, while T _1,fat (300 ms) was independent of NiCl ₂ concentration.
Conclusion: Novel quantitative MRI phantoms that mimic the simultaneous presence of fat, iron, and fibrosis in the liver were successfully developed and validated.
(© 2020 International Society for Magnetic Resonance in Medicine.)