Detecting Portal Venous Blood Flow in Metabolic Dysfunction-Associated Fatty Liver Disease Using Non-Invasive Doppler Ultrasound.

Introduction Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common liver disease and is associated with metabolic syndrome, obesity, and insulin resistance. MAFLD has been shown to produce changes in portal venous blood velocity and portal pressure before the development of cirrhosis. Accurate measurement of portal venous blood flow is essential for early detection of portal hypertension and assessing fibrosis risk. In this study, we aim to evaluate non-invasive transcutaneous Doppler ultrasound versus invasive direct techniques for detecting portal venous blood flow changes in a rat model of MAFLD. Methods We induced MAFLD in rats by a high-fat diet (HFD). Male Sprague Dawley rats (n=16) were housed in pairs under standard conditions (12-hour light/dark cycle, temperature-controlled environment at 20-23°C) with ad libitum access to water. After a two-day acclimation period, rats were divided into standard chow diet (STD) and HFD groups (n=8 each) for 10 weeks. Portal venous blood flow was first measured non-invasively via transcutaneous Doppler ultrasound and then directly using a flow probe during terminal surgery. Additionally, peak portal venous blood flow was compared between fed and fasted states (n=3 each) using non-invasive ultrasound. Animals were randomized to the order of testing and were anesthetized prior to ultrasound using isoflurane. Each measurement was collected in triplicate by same operator and averaged. Results Direct measurements indicated significantly higher portal venous blood flow in HFD rats (23.4 ± 2.8 mL/min) compared to STD rats (18.0 ± 2.4 mL/min, p<0.05). However, non-invasive Doppler ultrasound did not show significant differences between HFD (13.2 ± 1.0 mL/min) and STD (12.5 ± 1.8 mL/min, p=0.74). Importantly, transcutaneous Doppler ultrasound detected a significant increase in peak portal venous blood flow in the fed state (213.9 ± 24.9 mL/min) versus the fasted state (125.5 ± 24.1 mL/min, p<0.05). Conclusion Non-invasive Doppler ultrasound did not detect absolute portal flow differences between HFD and STD rats but successfully identified feeding-state changes. This suggests potential use in monitoring hemodynamic changes, though further refinement and validation in larger models are needed for clinical application. Limitations include a small sample size, particularly in the fed versus fasted analysis, and the exclusive use of male rats. The accuracy of transcutaneous Doppler ultrasound was hindered by technical challenges, including difficulty imaging small vessels, operator dependency, and assumptions about vessel geometry. Additionally, non-invasive measurements significantly underestimated actual flow compared to invasive methods. These factors limit the generalizability and clinical translation of the findings, underscoring the need for further validation in larger animal models and refinement of imaging techniques.