Evaluation of a motion-robust 2D chemical shift-encoded technique for R2* and field map quantification in ferumoxytol-enhanced MRI of the placenta in pregnant rhesus macaques.

Background: 3D chemical shift-encoded (CSE)-MRI techniques enable assessment of ferumoxytol concentration but are unreliable in the presence of motion.
Purpose: To evaluate a motion-robust 2D-sequential CSE-MRI for R2* and B0 mapping in ferumoxytol-enhanced MRI of the placenta.
Study Type: Prospective.
Animal Model: Pregnant rhesus macaques.
Field Strength/sequence: 3.0T/CSE-MRI.
Assessment: 2D-sequential CSE-MRI was compared with 3D respiratory-gated CSE-MRI in placental imaging of 11 anesthetized animals at multiple timepoints before and after ferumoxytol administration, and in ferumoxytol phantoms (0 μg/mL-440 μg/mL). Motion artifacts of CSE-MRI in 10 pregnant women without ferumoxytol administration were assessed retrospectively by three blinded readers (4-point Likert scale). The repeatability of CSE-MRI in seven pregnant women was also prospectively studied.
Statistical Tests: Placental R2* and boundary B0 field measurements (ΔB0) were compared between 2D-sequential and 3D respiratory-gated CSE-MRI using linear regression and Bland-Altman analysis.
Results: In phantoms, a slope of 0.94 (r ² = 0.99, concordance correlation coefficient ρ = 0.99), and bias of -4.8 s ^-1 (limit of agreement [LOA], -41.4 s ^-1 , +31.8 s ^-1 ) in R2*, and a slope of 1.07 (r ² = 1.00, ρ = 0.99) and bias of 11.4 Hz (LOA -12.0 Hz, +34.8 Hz) in ΔB0 were obtained in 2D CSE-MRI compared with 3D CSE-MRI for reference R2* ≤390 s ^-1 . In animals, a slope of 0.92 (r ² = 0.97, ρ = 0.98) and bias of -2.2 s ^-1 (LOA -55.6 s ^-1 , +51.3 s ^-1 ) in R2*, and a slope of 1.05 (r ² = 0.95, ρ = 0.97) and bias of 0.4 Hz (LOA -9.0 Hz, +9.7 Hz) in ΔB0 were obtained. In humans, motion-impaired R2* maps in 3D CSE-MRI (Reader 1: 1.8 ± 0.6, Reader 2: 1.3 ± 0.7, Reader 3: 1.9 ± 0.6), while 2D CSE-MRI was motion-free (Reader 1: 2.9 ± 0.3, Reader 2: 3.0 ± 0, Reader 3: 3.0 ± 0). A mean difference of 0.66 s ^-1 and coefficient of repeatability of 9.48 s ^-1 for placental R2* were observed in the repeated 2D CSE-MRI.
Data Conclusion: 2D-sequential CSE-MRI provides accurate R2* and B0 measurements in ferumoxytol-enhanced placental MRI of animals in the presence of respiratory motion, and motion-robustness in human placental imaging.
Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:580-592.
(© 2019 International Society for Magnetic Resonance in Medicine.)