Liver Fat Quantification (PDFF) Explained: MRI vs. Blood Tests vs. Ultrasound

Liver fat quantification measures how much fat is stored in the liver. MRI-PDFF provides a quantitative liver-fat percentage, while blood tests assess liver injury and fibrosis risk, and ultrasound-based methods identify or estimate steatosis.

FibroScan with CAP can assess liver fat and stiffness, while LiverMultiScan combines MRI-derived liver-fat measurement with additional biomarkers for broader liver assessment.

Hepatic steatosis occurs when excess fat, mainly triglycerides, accumulates inside liver cells. It is commonly associated with obesity, insulin resistance, type 2 diabetes and metabolic syndrome, although alcohol exposure, medications and other liver conditions can also contribute.

The World Health Organization (WHO) identifies excess body weight, unhealthy diets and physical inactivity as important risk factors for chronic non-communicable diseases, including diabetes and cardiovascular disease.

Simply being told that you have fatty liver does not indicate exactly how much fat is present. Conventional ultrasound may suggest hepatic steatosis through increased liver echogenicity, whereas MRI-PDFF (proton density fat fraction) uses novel magnetic resonance imaging techniques to provide a numerical estimate of liver fat.

Blood tests provide different information. ALT and AST can indicate hepatocellular injury, while platelet count and other laboratory values can contribute to fibrosis-risk calculations such as FIB-4. These tests do not directly measure liver fat as a percentage.

Liver-fat quantification is particularly useful when clinicians need to assess the degree of hepatic steatosis, monitor changes over time or evaluate treatment response. MRI-PDFF is valuable in these situations because it provides a reproducible, non-invasive measurement across a large portion of the liver.

Historically, liver biopsy was used to grade steatosis and assess other histological features of liver disease. Although biopsy remains important in selected situations, it is invasive and samples only a small part of the liver. MRI-PDFF provides a non-invasive quantitative alternative for assessing hepatic fat.

The term non-alcoholic fatty liver disease (NAFLD) is increasingly being replaced by metabolic dysfunction-associated steatotic liver disease (MASLD).

MASLD refers to steatotic liver disease occurring alongside one or more cardiometabolic risk factors, such as overweight or obesity, type 2 diabetes or other metabolic abnormalities, without harmful alcohol intake being the primary cause. The disease spectrum can include steatosis, metabolic dysfunction-associated steatohepatitis (MASH), fibrosis, cirrhosis and related complications.

The 2024 EASL-EASD-EASO guideline uses MASLD and MASH as the preferred terminology while recognising that NAFLD and NASH remain widely used in older literature.

This terminology places greater emphasis on metabolic health and the cardiometabolic risk factors that commonly accompany fatty liver disease.

MRI-PDFF, LiverMultiScan, blood tests, conventional ultrasound and FibroScan with controlled attenuation parameter (CAP) provide different types of information.

MRI-PDFF stands for magnetic resonance imaging proton density fat fraction. It is an advanced MRI technique that separates fat and water signals to calculate the proportion of fat within liver tissue.

Unlike conventional ultrasound, which may describe the liver as mildly or moderately fatty, MRI-PDFF can provide a numerical liver-fat fraction.

It has several advantages:

• Provides a quantitative liver-fat percentage

• Does not use ionising radiation

• Covers a large portion of the liver

• Has good repeatability and reproducibility

• Can detect changes in liver fat over time

• Is useful in clinical research and treatment-response assessment

MRI-PDFF has also been extensively evaluated against liver biopsy and other reference methods. It is particularly useful when the clinical question is: "How much fat is present in the liver?"

However, MRI-PDFF is not a complete assessment of liver disease. It does not independently determine the presence or severity of every type of liver inflammation, viral hepatitis or fibrosis.

LiverMultiScan is a multiparametric MRI-based technology that provides quantitative information about liver fat, liver tissue characteristics and iron.

Depending on the protocol, LiverMultiScan can provide measurements including:

• PDFF: estimates liver fat

• cT1: provides information associated with liver tissue changes and disease activity

• T2* or liver-iron measurements: assess hepatic iron

MRI-PDFF is a specific quantitative measurement of liver fat, while LiverMultiScan uses PDFF as one component of a broader multiparametric MRI assessment. In other words, LiverMultiScan is not simply another name for MRI-PDFF. A LiverMultiScan assessment can potentially provide information about:

1. How much fat is present in the liver

2. Whether there are MRI-derived features associated with fatty liver disease activity

3. Whether there is excess liver iron

This can make multiparametric MRI useful when a clinician wants more information than liver-fat percentage alone can provide.

However, LiverMultiScan does not mean that every liver condition can be assessed with one scan. Blood tests, elastography or specialist evaluation may still be required depending on the individual's clinical situation.

Routine blood tests cannot directly calculate the percentage of fat in the liver. While a standard fatty liver blood test cost is relatively low compared to advanced MRI imaging, panel prices vary depending on whether you order standalone liver enzymes (ALT/AST) or comprehensive metabolic panels. ALT and AST are commonly measured to look for evidence of hepatocellular injury.

The fibrosis-4 body mass index, or FIB-4, uses:

• Age

• AST

• ALT

• Platelet count

to estimate the likelihood of advanced liver fibrosis.

The 2023 AASLD Practice Guidance recommends further evaluation for people with steatosis on imaging or clinical suspicion of fatty liver disease. It supports FIB-4 as an initial risk-stratification tool, followed by vibration-controlled transient elastography (VCTE/FibroScan), ELF testing or other assessment when indicated.

The 2024 EASL-EASD-EASO guideline similarly recommends a stepwise approach using blood-based scores such as FIB-4 followed by imaging-based non-invasive tests such as transient elastography when appropriate.

Blood testing may therefore be combined with glucose, HbA1c, lipid profile, complete blood count and other metabolic parameters to understand the broader risk profile.

Conventional abdominal ultrasound is frequently used as an initial imaging test when fatty liver is suspected.

It looks for features such as increased hepatic echogenicity. However, conventional ultrasound is primarily qualitative or semi-quantitative.

Ultrasound can suggest fatty liver but cannot reliably provide an exact liver-fat percentage. It is also less sensitive for mild steatosis than quantitative MRI techniques.

MRI is demonstrably superior for diagnostic precision. Conventional ultrasound can only estimate fat qualitatively and often misses mild steatosis, whereas MRI-PDFF provides a quantitative percentage-based fat fraction regardless of body habitus.

Controlled attenuation parameter (CAP) is an ultrasound-based measurement used to estimate hepatic steatosis. CAP is commonly available with transient elastography systems such as FibroScan. It measures the attenuation of ultrasound signals as they travel through liver tissue.

Higher CAP measurements generally indicate greater hepatic fat accumulation. CAP has been compared with MRI-PDFF in multiple studies. Its performance can vary according to body habitus, probe type, degree of steatosis and other technical factors. Therefore, CAP should not be treated as a direct substitute for an MRI-PDFF liver-fat percentage.

FibroScan is a non-invasive transient elastography technology that can assess liver stiffness and, when CAP is available, estimate liver steatosis.

It can provide two important measurements:

• CAP → estimates liver fat

• Liver stiffness measurement (LSM) → helps assess fibrosis risk

This makes FibroScan particularly useful when the clinical question includes both fatty liver and possible fibrosis.

The 2023 AASLD guidance identifies vibration-controlled transient elastography as an appropriate secondary assessment after FIB-4 in many patients requiring further fibrosis risk stratification.

The 2024 EASL-EASD-EASO guideline also includes transient elastography in its stepwise non-invasive assessment pathway.

No. FibroScan with CAP is useful for estimating liver steatosis, but MRI-PDFF is generally better established for precise quantitative liver-fat measurement.

The two methods report different measurements:

• MRI-PDFF reports proton density fat fraction as a percentage

• CAP reports ultrasound attenuation in dB/m

• CAP is affected by factors such as body habitus and technical characteristics

• MRI-PDFF provides broader liver coverage and more direct quantitative information

FibroScan has an important advantage: it can assess liver stiffness and steatosis during the same examination.

Therefore, the choice depends on the clinical question. FibroScan may be highly useful for fibrosis-risk assessment and routine steatosis evaluation, whereas MRI-PDFF is generally preferred when an accurate numerical measurement of liver fat is specifically required.

MRI-PDFF is generally the preferred non-invasive method when precise quantitative liver-fat measurement is required.

Research comparing MRI-PDFF with histological assessment has demonstrated strong diagnostic performance for detecting and grading steatosis.

FibroScan CAP is also useful, particularly because it is quick, non-invasive and can provide liver-stiffness information alongside steatosis assessment. However, CAP provides an indirect attenuation-based measurement rather than the same percentage-based fat fraction produced by MRI-PDFF.

Blood tests have a different purpose. They help identify biochemical abnormalities and estimate fibrosis risk but do not directly quantify liver fat.

An MRI-PDFF value below approximately 5% is commonly used as a reference threshold for non-steatotic liver.

An MRI-PDFF value of 5% or higher generally suggests hepatic steatosis, although exact thresholds vary according to the MRI technique, study population and clinical context.

Research studies may use higher thresholds to distinguish increasing degrees of steatosis, but these should not automatically be applied as universal clinical grades.

Liver-fat percentage does not tell you whether you have liver inflammation or advanced fibrosis. These are separate clinical questions that may require liver enzymes, FIB-4, FibroScan/VCTE, magnetic resonance elastography or specialist evaluation.

MRI liver-fat quantification prices in India vary widely depending on the city, diagnostic centre, MRI strength, protocol and whether PDFF analysis is included.

The price range in the original draft should be treated as an indicative range rather than a fixed national price. Before publishing a specific ₹4,500–₹11,500 figure, it is better to verify the current listings for the target city because specialised MRI pricing can change.

When comparing prices, check whether the quoted amount includes:

• MRI liver-fat quantification/PDFF

• Image acquisition

• PDFF post-processing

• Radiologist reporting

• Additional MRI sequences

• Contrast, if clinically required

A routine liver MRI and an MRI specifically analysed for PDFF are not necessarily the same examination.

MRI-PDFF has strong evidence supporting quantitative liver-fat assessment. FibroScan CAP can detect and estimate steatosis but is not interchangeable with MRI-PDFF.

Conventional ultrasound is useful for detecting more obvious fatty infiltration but has lower sensitivity for mild steatosis.

Blood tests are not liver-fat quantification tests. ALT and AST can indicate liver injury, while FIB-4 is used for fibrosis-risk stratification.

Blood tests are generally the most accessible and least expensive option. Conventional ultrasound is also widely available and relatively affordable.

FibroScan is generally more accessible and less expensive than MRI-based liver-fat quantification, although availability varies between cities and centres.

MRI-PDFF and LiverMultiScan require specialised MRI equipment and analysis, making them more expensive and less widely available.

Blood tests usually involve a simple blood draw. Ultrasound and FibroScan are non-invasive examinations and are generally completed relatively quickly.

MRI-PDFF requires the patient to remain still inside the MRI scanner. Breath-holding instructions may be required during some sequences.

LiverMultiScan similarly requires MRI acquisition followed by specialised image analysis. Reporting time depends on the diagnostic centre, radiologist and whether specialised post-processing is required.

The right test depends on what you need to find out.

• Initial liver and metabolic assessment: Blood tests may be an appropriate starting point.

• Suspected fatty liver: Ultrasound may be used for initial imaging.

• Fibrosis-risk assessment: FIB-4 followed by FibroScan/VCTE or another non-invasive test may be appropriate.

• Precise liver-fat measurement: MRI-PDFF is generally preferred.

• Liver fat plus stiffness assessment: FibroScan with CAP can provide both measurements.

• Multiparametric MRI assessment: LiverMultiScan can provide PDFF alongside additional MRI-derived biomarkers.

• Treatment-response monitoring: MRI-PDFF can provide reproducible numerical measurements of liver fat.

• Uncertain or chronic liver disease: Gastroenterology or hepatology evaluation may be required.

The 2024 EASL-EASD-EASO guideline supports a stepwise approach using blood-based scores such as FIB-4 and, when indicated, imaging-based non-invasive tests such as transient elastography.

An abnormal liver-fat measurement does not automatically mean advanced liver disease.

A healthcare professional may assess:

• Body weight and metabolic risk factors

• Diabetes or insulin resistance

• Cholesterol and triglycerides

• Alcohol exposure

• Medications and herbal supplements

• ALT and AST

• Platelet count

• FIB-4 score

• Liver stiffness

• Other causes of liver disease

The next investigation depends on the overall clinical picture.

For example, someone with steatosis and a low fibrosis-risk score may need monitoring and management of metabolic risk factors, whereas someone with an elevated FIB-4 may need FibroScan or specialist evaluation.

MyDiagnostics can be used for blood-based liver health screening and broader health assessment, including laboratory investigations relevant to liver and metabolic health.

Blood tests can be a useful starting point when the clinical goal is to assess liver enzymes and associated metabolic risk before deciding whether further imaging is needed.

For people specifically looking for MRI-based liver-fat assessment, MyDiagnostics also offers its Vital Full Body MRI Scan, which includes liver-related MRI assessment and liver-fat analysis. The exact MRI protocol, including whether a specific PDFF sequence or analysis is included, should be confirmed at the time of booking.

This distinction is important:

Blood testing helps assess liver injury and metabolic/fibrosis risk; MRI-based testing is used when quantitative imaging assessment of liver fat is required.

If you specifically need a standalone MRI-PDFF, LiverMultiScan or FibroScan, confirm availability and the exact protocol with the diagnostic centre before booking, because these investigations are not interchangeable.