Multi-Center, Multi-Vendor Validation of Simultaneous MRI-Based Proton Density Fat Fraction and R2* Mapping Using a Combined Proton Density Fat Fraction-R2* Phantom.

Background: Fat and iron deposition confound measurements of R2* and proton density fat fraction (PDFF), respectively, yet their combined impact on reproducibility is poorly understood.

Purpose: To evaluate the multi-center, multi-vendor reproducibility of PDFF and R2* quantification using a PDFF-R2* phantom.

Study Type: Prospective multi-center, phantom study.

Phantom: Commercial PDFF-R2* phantom with simultaneously controlled combination of PDFF (0%-30%) and R2* (50-600 s) values.

Field Strength/sequence: 1.5-T and 3-T, three-dimensional (3D) multi-echo, spoiled-gradient-echo sequences, in four different centers, each with a different vendor.

Assessment: Two acquisition protocols were used, optimized for moderate R2* (Protocol 1) and high R2* (Protocol 2), respectively. The phantom was imaged multiple times at one of the centers to assess its stability.

Statistical Tests: Intraclass correlation coefficient (ICC), linear regression analysis, reproducibility coefficient (RDC) and repeatability coefficient (RC).

Results: Excellent agreement was observed for PDFF measurements between centers, vendors, field strengths, and protocols (ICC = 0.97). Stratified by protocol, excellent agreement was observed, with ICC = 0.96 (RDC = 6.2%) for Protocol 1 and ICC = 0.99 (RDC = 3.8%) for Protocol 2. Increased variability in PDFF measurements was observed with increasing PDFF and especially with higher R2*. Excellent agreement was observed for R2* between centers, vendors, field strengths, and protocols (ICC = 0.99). Stratified by protocol, strong agreement was observed, with ICC = 0.988 (RDC = 66.7 s) for Protocol 1 and ICC = 0.99 (RDC = 57.7 s) for Protocol 2. Higher variability in R2* measurements was observed in vials with higher PDFF or R2*. Stability tests demonstrated an ICC = 1.0 for PDFF and R2*, and RC of 0.4% for PDFF and 12 s for R2*.

Data Conclusion: Excellent PDFF and R2* reproducibility was observed across centers, vendors, field strengths, and acquisition protocols. Reproducibility decreased slightly with increasing PDFF and R2*, especially for PDFF measurements in vials with high R2*.

Evidence Level: N/A.

Technical Efficacy: Stage 1.