Liver MRI: Quantifying Iron and Fat (T2* and PDFF)
MRI measures two numbers in the liver, how much iron and how much fat, non-invasively instead of by biopsy.
Liver iron: T2* / R2*
Iron is strongly paramagnetic and accelerates signal decay, so the more iron in the liver, the shorter the T2* (higher R2*). Calibrated sequences convert this into a liver iron concentration, guiding chelation in transfusion-dependent patients and diagnosing overload states like haemochromatosis.
Liver fat: proton density fat fraction (PDFF)
MRI can separate the signal from water and fat protons to compute the proton density fat fraction, the percentage of liver made up of fat. PDFF is accurate, reproducible across scanners when done properly, and sensitive to small changes, making it valuable for diagnosing and monitoring steatosis (MASLD/NAFLD) and as an endpoint in drug trials.
Why it matters
- Avoids biopsy: sampling error and complications of needle biopsy are removed; the whole liver is assessed.
- Quantitative follow-up: treatment response (chelation, lifestyle, drugs) is tracked with real numbers.
- Often paired with MR elastography for fibrosis, together giving iron, fat and stiffness in one visit.
Sources
- Reeder SB et al. Quantification of hepatic steatosis with MRI: the effects of accurate fat-fraction estimation. J Magn Reson Imaging 2011;34:729–49.
Educational summary for clinicians; calibration and thresholds are technique-dependent. Not medical advice.