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Published on: September 7, 2018
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Limitations of Bone Marrow Relative Fat Fraction Compared With Proton Density Fat Fraction
Tamara Scott1,2, Matthew Mader1, Rianne A van der Heijden1,3
1Department Radiology, University of Wisconsin-Madison, Madison, WI.
Journal of Computer Assisted Tomography
|November 17, 2025
Summary
Relative fat fraction (rFF) MRI measurements of bone marrow fat are inaccurate and should not be used. Proton density fat fraction (PDFF) is a more reliable MRI metric for assessing bone marrow fat content.
Area of Science:
- Radiology
- Medical Imaging
- Oncology
Background:
- Relative fat fraction (rFF) using dual-echo gradient-recalled echo (GRE) in- and opposed-phase (IOP) MRI has been proposed for evaluating multiple myeloma treatment response.
- However, rFF has significant limitations leading to inaccurate bone marrow fat fraction measurements.
- Proton density fat fraction (PDFF) measured by confounder-corrected, multiecho, chemical-shift-encoded (CSE) MRI is a validated and objective metric for tissue fat content.
Purpose of the Study:
- To evaluate the linearity and bias of bone marrow rFF compared to PDFF.
Main Methods:
- Retrospective study of 100 patients (1.5T and 3.0T MRI) including dual-echo GRE IOP and multiecho CSE MRI (IDEAL-IQ).
- Regions of interest (ROIs) placed in T12, L1, and L2 vertebral bodies.
- rFF calculated from signal intensities; correlation with PDFF using linear regression (R2) and Bland-Altman analysis for bias.
Main Results:
- Bone marrow rFF showed no linearity against PDFF at 1.5T (R2 = 0.032) or 3.0T (R2 = 0.057).
- Significant bias was observed between rFF and PDFF at both field strengths.
- Bias increased directly with bone marrow fat fraction.
Conclusions:
- Bone marrow rFF is nonlinear and variably biased compared to PDFF.
- rFF should not be used in research or clinical settings for bone marrow fat assessment.
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