Prior to the curative resection of colorectal carcinoma (CRC) or pancreatic ductal adenocarcinoma (PDAC), the exclusion of hepatic metastasis using cross-sectional imaging is mandatory. The Doppler perfusion index (DPI) of the liver is a promising method for detecting occult liver metastases, but the underlying visceral duplex sonography is critically viewed in terms of its reproducibility. The aim of this study was to investigate systematically the reproducibility of the measured variables, the calculated blood flow, and the DPI. Between February and September 2023, two examinations were performed on 80 subjects within a period of 0–30 days and at two previously defined quality levels, aligned to the German standards of the DEGUM. Correlation analyses were carried out using Pearson’s correlation coefficient (PCC) and the intraclass correlation coefficient (ICC). The diameters, blood flow, and DPI showed a high degree of agreement (PCC of 0.9 and ICC of 0.9 for AHP). Provided that a precise standard of procedure is adhered to, the Doppler examination of AHC, AHP, and PV yields very reproducible blood flows and DPI, which is a prerequisite for a comprehensive investigation of its prognostic value for the prediction of metachronous hepatic metastasis in the context of curatively treated CRC or PDAC.

Background/Objectives: The Doppler perfusion index (DPI) quantifies the ratio of arterial to total hepatic blood flow and reflects hepatic hemodynamic balance. Its clinical applicability is limited by insufficient standardization and the absence of clearly defined physiological reference conditions. This study aimed to establish an upper physiological reference limit for the DPI and to assess its dependence on standardized physiological conditions in healthy adults. Methods: In this prospective study, 44 healthy adults underwent Doppler ultrasonography under standardized conditions (fasting/resting, post-exercise, postprandial). Volumetric blood flow was measured in the portal vein and via the proper hepatic artery and, where feasible, the common hepatic artery. The DPI was calculated as the ratio of arterial to total hepatic inflow. Nonparametric statistical methods were applied. Results: After exclusion of participants with non-standard hepatic arterial anatomy, 39 individuals were analyzed. The DPI varied across physiological conditions, reflecting changes in the relative contributions of arterial and portal venous inflow. Under fasting/resting conditions, values based on the proper hepatic artery showed low variability (mean 0.242 ± 0.057) and normal distribution (Shapiro–Wilk p = 0.625). The empirically derived 90th percentile was 0.30. Measurements based on the common hepatic artery were higher and more variable. Conclusions: The DPI is a physiologically dynamic parameter whose clinical use requires standardized measurement conditions. Under defined protocols, a value of approximately 0.30 may be considered an upper physiological reference limit. Standardization of acquisition and use of the proper hepatic artery enable reproducible and interpretable measurements. This provides a methodological basis for further clinical applications, including oncological contexts in which functional alterations of hepatic perfusion may be relevant.