This study investigates a new, simplified approach to measuring blood pressure within the liver (portal hypertension) using Endoscopic Ultrasound-Guided Portal Pressure Gradient Measurement (EUS-PPG). While this minimally invasive method traditionally relies on a hepatic vein as the baseline reference point, advanced liver scarring can make these veins twisted and highly difficult to access. To address this challenge, our study evaluates the Inferior Vena Cava (IVC)-the body's largest main vein-as an alternative reference site. Currently, it remains scientifically unproven whether the inferior vena cava or the hepatic vein provides the more reliable and accurate pressure reading for calculation, as anatomical distortion from cirrhosis can affect both areas differently. By measuring and comparing both venous compartments during a single, clinically scheduled endoscopy session, this study aims to determine if the pressures are truly interchangeable. Ultimately, this research will clarify which vessel serves as the optimal reference point, helping to establish a safer, more reliable diagnostic standard for patients with complex vascular anatomy.

Inclusion Criteria:

• Consecutive adult patients (≥18 years) undergoing clinically indicated EUS-guided portal pressure gradient measurement

Exclusion Criteria:

• severe coagulopathy (INR >2.0), thrombocytopenia (<50,000/µL)
• large-volume ascites
• gastric varices precluding safe vascular puncture
• known hepatic vein thrombosis or Budd-Chiari syndrome
• altered IVC anatomy such as patients after liver transplantation with piggy-back anastomosis
• contraindication to upper gastrointestinal endoscopy or sedation
• pregnancy

The study population consists of consecutive adult patients ($\ge18$ years) undergoing a clinically indicated EUS-PPG measurement (e.g., for liver disease evaluation, fibrosis staging, or portal hypertension assessment).