# Liver fat quantification (MRI-PDFF)

MRI-PDFF (proton density fat fraction) measures the share of your liver's protons that belong to fat triglycerides, versus all its water and fat protons. The result is a percentage that directly reflects how much fat is in your liver. The scan uses a multi-echo, chemical-shift method that separates water and fat signals, while correcting for several confounders (T1 bias, T2* decay, and the spectral complexity of fat). Simpler in-and-out-of-phase scans cannot correct for those. A PDFF above 5% defines liver steatosis, the threshold for metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD). Permutt et al. (2012) studied 51 biopsy-confirmed patients and found a strong correlation with steatosis grade (r² = 0.56, p < 0.0001). Mean PDFF was 8.9% for grade 1, 16.3% for grade 2, and 25.0% for grade 3. In trials, MRI-PDFF has largely replaced needle biopsy, because it samples the whole liver. A 30% relative drop from baseline is linked to resolution of MASH on biopsy, and is now a common trial endpoint. Excess liver fat speeds insulin resistance and carries its own heart risk, which makes MRI-PDFF a longevity-relevant marker. One limit: it does not directly measure fibrosis, the stage most predictive of liver-related death.

## Sources

- Permutt Z, Le T-A, Peterson MR, Seki E, Brenner DA, Sirlin C, et al.. (2012). Correlation between liver histology and novel magnetic resonance imaging in adult patients with non-alcoholic fatty liver disease – MRI accurately quantifies hepatic steatosis in NAFLD. Alimentary Pharmacology & Therapeutics. https://doi.org/10.1111/j.1365-2036.2012.05121.x
- Dulai PS, Sirlin CB, Loomba R. (2016). MRI and MRE for non-invasive quantitative assessment of hepatic steatosis and fibrosis in NAFLD and NASH: Clinical trials to clinical practice. Journal of Hepatology. https://doi.org/10.1016/j.jhep.2016.06.005
- Caussy C, Reeder SB, Sirlin CB, Loomba R. (2018). Noninvasive, Quantitative Assessment of Liver Fat by MRI-PDFF as an Endpoint in NASH Trials. Hepatology. https://doi.org/10.1002/hep.29797

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_Canonical: https://longevity-switzerland.com/en/glossary/liver-fat-mri-pdff · Part of Longevity Cities · Updated 2026-06-22_