The study shows that a MRI‑based measure called the gadoxetic acid uptake rate (k1) combined with liver size (k1VL) lines up well with traditional liver function tests, while the portal‑vein perfusion rate (kpv) does not. This imaging trick helps doctors see how well different parts of the liver are working, especially in sick livers, but it isn’t something you can use at home.

Global and regional liver function assessments are important for defining the magnitude and spatial distribution of dose to preserve functional liver parenchyma and reduce incidence of hepatotoxicity from radiation therapy for intrahepatic cancer treatment. This individualized liver function-guided radiation therapy strategy is critical for patients with heterogeneous and poor liver function, often observed in cirrhotic patients treated for hepatocellular carcinoma. This study aimed to validate <i>k₁</i> as a measure of global and regional function through comparison with 2 well-regarded global function measures: indocyanine green retention (ICGR) and albumin-bilirubin (ALBI). Seventy-nine dynamic gadoxetic acid enhanced magnetic resonance imaging scans were acquired in 40 patients with hepatocellular carcinoma in institutional review board approved prospective protocols. Portal venous perfusion (<i>k_pv</i> ) was quantified from gadoxetic acid enhanced magnetic resonance imaging using a dual-input 2-compartment model, and gadoxetic acid uptake rate (<i>k₁)</i> was fitted using a linearized single-input 2-compartment model chosen for robust <i>k₁</i> estimation. Four image-derived measures of global liver function were tested: (1) mean <i>k₁</i> multiplied by liver volume (<i>k₁V_L</i> ) (functional volume), (2) mean <i>k₁</i> multiplied by blood distribution volume (<i>k₁V_dis</i> )_, (3) mean <i>k_pv,</i> and (4) liver volume (<i>V_L</i> ). The measure's correlation with corresponding ICGR and ALBI tests was assessed using linear regression. Voxel-wise similarity between <i>k₁</i> and <i>k_pv</i> was compared using Spearman ranked correlation. Significant correlations (<i>P</i> &lt; .05) with ICGR and ALBI were found for <i>k₁V_L, k₁V_dis,</i> and <i>V_L</i> (in order of strength), but not for mean <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>k</mml:mi></mml:math> <i>_pv</i> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>.</mml:mo></mml:math> The mean ranked correlation coefficient between <i>k₁</i> and <i>k_pv</i> maps was 0.09. <i>k₁</i> and <i>k_pv</i> maps were predominantly mismatched in patients with poor liver function. The metric combining function and liver volume (<i>k₁V_L</i> ) was a stronger measure of global liver function compared with perfusion or liver volume alone, especially in patients with poor liver function. Gadoxetic acid uptake rate is promising for both global and regional liver function.