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

Abstract

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 (r2 = 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 (r2 = 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 (r2 = 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 (r2 = 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.

Reproducibility of liver R2* quantification for liver iron quantification from cardiac R2* acquisitions

“…In their study, the relationship between R2* and iron content was highly linear for R2* values up to 1200 s −1 , for both 2D and 3D CSE-MRI, so long as high SNR source images were used. However, when the SNR performance was similar to that expected with clinical 2D and 3D CSE-MRI acquisitions, the relationship between R2* and iron content only showed a linear relationship up to 400 s −1 and 500 s −1 , for 2D and 3D acquisitions, respectively [33].…”

“…As Zhu et al have recently shown in a phantom study, reliable measurement of R2* using 2D and 3D CSE-MRI depends on the signal-to-noise (SNR) ratio [33]. In their study, the relationship between R2* and iron content was highly linear for R2* values up to 1200 s −1 , for both 2D and 3D CSE-MRI, so long as high SNR source images were used.…”

Quantitative ferumoxytol-enhanced MRI in pregnancy: A feasibility study in the nonhuman primate

“…5 and Table 3. Example ROIs are shown in a previous study [31]. Placental R2* and susceptibility increased significantly after ferumoxytol administration at Day 0-post (P < 0.001).…”

Performing Quality Control on Magnetic Resonance Imaging Liver Fat/Iron Quantification Studies: A Critical Requirement

“…Review of water only image motion artifacts according to a Likert scale 17 : 5 = no motion, 4 = insignificant motion, 3 = moderate motion, 2 = significant motion, and 1 = severe motion (Fig. 2).…”