Interactive Steatosis Mapper: liver CT attenuation reading with estimated MRI-PDFF and histological grade.
Created by Dr. Sharad Maheshwari MD - imagingsimplified@gmail.com
Founder: BeResponsibleAI
CT-Based Steatosis & MASH Triage
Adjust the sliders below based on any non-contrast 120 kV CT (ideal for both dedicated abdominal imaging and opportunistic screening). The tool will calculate estimated PDFF, MASH risk, and automatically generate an actionable reporting phrase in the next tab.
Clinical Biomarkers (MASH Triad)
High MASH Probability
Combination of liver attenuation ≤ 40 HU and abnormal biomarkers generates a highly predictive composite risk for MASH.
⚙ Automated Clinical Synthesis
Adjust the sliders to generate a clinical synthesis.
📄 Generated Dictation Template
Live OutputNormal / Minimal Fat
Clinical Context & Rationale
Context will appear here based on selected parameters.
Evidence & Scientific Rationale
The algorithms powering this dashboard rely on established physical principles and massive published cohorts to serve as a robust categorical triage tool.
HU-PDFF Correlation Curve
Visualizing the inverse non-linear relationship between non-contrast 120 kV CT attenuation and MRI-PDFF (the non-invasive gold standard).
1 Tool Logic: The "Gatekeeper"
The calculator uses a Gatekeeper logic system. The CT scan detects the presence of structural fat, while labs (ALT, HDL-C) detect active inflammation and systemic metabolic dysfunction.
A. The Gatekeeper: CT Attenuation (≤ 40 HU)
Lab values will only trigger a MASH alert if HU is ≤ 40 (the published gold-standard cutoff for moderate/severe steatosis). Without structural fat, elevated ALT indicates a different etiology entirely (e.g., viral or drug-induced injury).
B. The Triggers (The Composite Triad)
If HU ≤ 40, the tool evaluates the labs. Entering ALT > 40 U/L or HDL-C < 1.1 mmol/L meets the Composite Triad, triggering the high-risk MASH alert UI.
2 The Physical Principle
- ✔ Normal liver parenchyma is roughly 55 to 65 HU on a non-contrast scan. Fat has a negative attenuation (roughly -50 to -100 HU).
- ✔ Because a CT voxel represents average attenuation, as macroscopic fat droplets replace hepatocytes, overall attenuation drops predictably.
3 Biomarker Selection: Why ALT & HDL-C?
The Primary Independent Predictors
ALT (Alanine Transaminase)
The primary driver for active hepatocellular injury. As fat causes cellular ballooning, ALT leaks into the bloodstream.
HDL-C (High-Density Lipoprotein)
Uniquely tied to systemic metabolic dysfunction. Severe hepatic insulin resistance increases CETP activity, stripping cholesterol from HDL particles. A dropping HDL-C is a highly validated surrogate for MASH progression.
📖 Mandatory References
Opportunistic CT Screening (The 40 HU Standard)
Pickhardt, P. J., et al. Pivotal population studies defining the ≤ 40 HU threshold for moderate-to-severe steatosis.
View Literature Search →Living Donor Liver Transplantation Cohorts (CT to Histology)
Park SH, et al. (Radiology 2006). The foundational transplant literature directly correlating unenhanced CT ≤ 40 HU with ≥ 30% macrovesicular steatosis (Histology S2) via liver wedge biopsies to prevent graft failure.
View Literature Search →HDL-C and Dyslipidemia in MASH
Literature linking severe insulin resistance, impaired ApoA-I synthesis, and dropping HDL-C.
View Literature Search →Comprehensive Liver Disease Knowledge Base
A clinical guide to understanding the spectrum of Steatotic Liver Disease, the recent shifts in nomenclature, and the broader clinical picture beyond initial imaging.
1. The Nomenclature Shift: NAFLD to MASLD
In 2023, major global hepatology societies replaced the term NAFLD (Non-Alcoholic Fatty Liver Disease) with MASLD (Metabolic Dysfunction-Associated Steatotic Liver Disease).
Why the change?
- It removes the stigmatizing terms "non-alcoholic" and "fatty."
- It establishes an affirmative diagnosis rather than an exclusionary one. A patient is diagnosed with MASLD if they have hepatic steatosis PLUS at least one cardiometabolic risk factor (e.g., obesity, type 2 diabetes, hypertension, or dyslipidemia).
2. Defining the Diagnostic Metrics
To understand steatosis evaluation, it is crucial to understand the three distinct ways we measure liver fat: Radiodensity (CT), Proton Fraction (MRI), and Histology (Biopsy).
CT Attenuation (Hounsfield Units / HU)
HU is a standard measure of radiodensity on a CT scan. Water is exactly 0 HU. A normal, healthy liver measures between 55 and 65 HU on a non-contrast scan. Because fat is lighter than water, it has a negative HU value (roughly -50 to -100). As microscopic fat accumulates inside the liver cells, it pulls the overall average density of the organ downward. Thus, a lower HU indicates more fat.
MRI-PDFF (Proton Density Fat Fraction)
MRI-PDFF is the non-invasive "gold standard" for quantifying liver fat. It uses advanced MRI physics to calculate the exact percentage of mobile protons in the liver that come from fat molecules versus water molecules. Unlike CT (which gives a blended density score), MRI-PDFF provides an absolute, quantitative percentage (e.g., 12.5% fat).
Histological Steatosis Grade (S0 - S3)
This is the microscopic assessment from an invasive liver biopsy. A pathologist examines the tissue sample and estimates the percentage of liver cells (hepatocytes) that contain visible fat droplets. The NASH Clinical Research Network (CRN) categorizes this into four distinct grades (S0, S1, S2, and S3).
| Biopsy Grade | Hepatocytes w/ Fat | Est. MRI-PDFF | CT Attenuation | Clinical Implication |
|---|---|---|---|---|
| S0 (Normal) | < 5% | < 5% | ≥ 55 HU | Low Risk |
| S1 (Mild) | 5% – 33% | 5% – 15% | 40 – 50 HU | Rising Risk |
| S2 (Moderate) | 34% – 66% | 15% – 24% | 30 – 40 HU | Clinically Important |
| S3 (Severe) | > 66% | ≥ 25% | < 30 HU | High MASH Prob. |
3. The Disease Spectrum
MASLD is not a single disease, but a progressive spectrum of liver injury driven by metabolic dysfunction:
Simple Steatosis (MASL)
Fat accumulation in >5% of hepatocytes without significant inflammation. Often asymptomatic and highly reversible with weight loss.
MASH (Steatohepatitis)
The fat causes cellular toxicity, leading to hepatocyte ballooning, inflammation, and cell death. This is the critical stage our calculator aims to flag early.
Fibrosis
Chronic inflammation leads to scar tissue formation. Graded F0 (none) to F4 (cirrhosis). This is the primary predictor of liver-related mortality.
Cirrhosis (F4) & HCC
End-stage liver architecture distortion. Patients are at risk for decompensation (ascites, varices) and Hepatocellular Carcinoma (HCC).
4. Beyond the Tool: The Full Lab Panel
While our calculator uses ALT and HDL-C to predict initial inflammation (MASH), managing the disease requires evaluating the entire clinical picture—specifically assessing for Fibrosis.
Markers of Fibrosis (Crucial for Prognosis)
- AST (Aspartate Transaminase): While less specific than ALT for early inflammation, AST levels often surpass ALT as the disease progresses to severe fibrosis and cirrhosis. The AST/ALT ratio is a key clinical metric.
- Platelet Count: A dropping platelet count is one of the earliest signs of portal hypertension, indicating advanced fibrosis/cirrhosis.
- FIB-4 Score Combining Age, AST, ALT, and Platelets generates the FIB-4 score, the gold-standard non-invasive triage test for ruling out advanced fibrosis.
Metabolic & Other Markers
- GGT (Gamma-Glutamyl Transferase): Often elevated in MASLD. It is a highly sensitive but non-specific marker of oxidative stress and biliary injury.
- Triglycerides & LDL-C: High triglycerides confirm dyslipidemia, and managing LDL-C is paramount because the leading cause of death in MASLD patients is cardiovascular disease, not liver failure.
- HbA1c & Fasting Glucose: Essential for evaluating the severity of insulin resistance and concurrent Type 2 Diabetes.
- Albumin & Bilirubin: These measure the liver's synthetic and excretory functions. They typically remain entirely normal until the liver reaches decompensated cirrhosis.
5. What about LAI (Liver Attenuation Index)?
Historically, radiologists frequently evaluated steatosis using the Liver-Spleen difference or ratio, collectively known as the Liver Attenuation Index (LAI).
The Logic: A normal liver is typically 5 to 10 HU brighter than the spleen. A Liver-Spleen difference of ≤ -10 HU (the liver is 10 units darker than the spleen) is a highly validated metric that strongly correlates with ≥ S2 steatosis and MRI-PDFF.
Why use absolute HU (≤ 40) in this tool instead of LAI?
- Field of View: In opportunistic screening (particularly chest CTs), the spleen is frequently not fully visible, making LAI impossible to calculate.
- Splenic Disease: Anemia, portal hypertension, or splenic congestion can alter spleen attenuation, introducing errors into the ratio.
- Global Standardization: Massive cohort studies have proven that an absolute liver attenuation of ≤ 40 HU is robust enough to stand on its own for diagnosing moderate-to-severe fat without needing an internal splenic control.
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