Magnetic Resonance Imaging-Proton Density Fat Fraction (MRI-PDFF) is a non-invasive imaging technique that has emerged as a reliable tool in medical diagnostics. Its primary purpose is to accurately measure fat content in various organs, particularly the liver. This method provides precise, quantitative data on organ fat.
What MRI-PDFF Measures
MRI-PDFF stands for Magnetic Resonance Imaging – Proton Density Fat Fraction. Magnetic Resonance Imaging operates by using strong magnetic fields and radio waves to generate detailed images of organs and tissues within the body. Unlike X-rays or CT scans, MRI does not involve ionizing radiation.
The “Proton Density Fat Fraction” component quantifies the percentage of fat relative to water within a given tissue. The technique acquires multiple echoes at different echo times, where fat and water signals are either in-phase or out-of-phase. Specialized software then processes this data, correcting for factors like T2 effects and fat signal modeling, to accurately calculate fat content. This approach ensures accurate and reliable fat quantification.
Its Importance in Liver Health
Measuring liver fat is significant, especially for conditions like Non-Alcoholic Fatty Liver Disease (NAFLD) and its more severe form, Non-Alcoholic Steatohepatitis (NASH). NAFLD is characterized by excessive fat accumulation in the liver, affecting over 20% of the population. NASH, a progressive form of NAFLD, carries a higher risk of advancing to cirrhosis and hepatocellular carcinoma, becoming a leading cause of liver transplantation.
MRI-PDFF aids in diagnosing these conditions by providing a precise, quantitative assessment of liver fat content, also known as hepatic steatosis. It helps monitor disease progression or regression in response to treatments or lifestyle changes, with a relative reduction of 29% to 30% in liver fat on MRI-PDFF associated with histological improvement in NASH. Furthermore, MRI-PDFF is increasingly used in clinical trials for new drug therapies targeting liver diseases, serving as an objective and quantitative biomarker to assess treatment response.
Comparing MRI-PDFF to Other Diagnostics
MRI-PDFF offers advantages over other methods used to assess liver fat. Liver biopsy, traditionally considered the gold standard, is an invasive procedure with risks like pain, bleeding, and, rarely, death. It samples only a small portion of the liver, which can lead to sampling errors and potentially false negative results. In contrast, MRI-PDFF is non-invasive and provides a quantitative assessment of fat content across the entire liver.
Compared to other imaging techniques like ultrasound and CT scans, MRI-PDFF demonstrates superior accuracy for liver fat. While ultrasound can qualitatively assess liver echogenicity, its accuracy for fat quantification is lower, especially for mild steatosis. CT scans can detect moderate to severe hepatic steatosis, but their utility is limited at low fat concentrations, and they involve ionizing radiation, making them less suitable for repeated examinations. MRI-PDFF is independent of acquisition parameters and platform differences, making it a highly repeatable and reproducible biomarker.
What to Expect and Understanding Your Results
Undergoing an MRI-PDFF scan is a straightforward process. You will lie still on a table that slides into the MRI machine, which can be noisy, but earplugs are typically provided. The scan duration is relatively short, often performed during a single breath-hold to ensure clear images.
Your MRI-PDFF results are typically reported as a percentage, indicating the proportion of fat in your liver. A PDFF value of less than 5% generally indicates normal liver fat content. Values above this threshold suggest hepatic steatosis, with increasing percentages correlating with higher grades of fat accumulation: mild, moderate, or severe. For example, a PDFF of 6.5–17.4% might indicate mild steatosis, while 22.2% or greater suggests severe steatosis. Discuss these results with your healthcare provider, who can interpret them within your overall clinical context and guide any necessary next steps.