Accurate quantification of regional liver function is needed, and PET of specific hepatic metabolic pathways offers a unique method for this purpose. Here, we quantify hepatic galactose elimination in humans using PET and the galactose analog 2-18F-fluoro-2-deoxy-d-galactose (18F-FDGal) as the PET tracer. Methods Eight healthy human subjects underwent 18F-FDGal PET/CT of the liver with and without a simultaneous infusion of galactose. Hepatic systemic clearance of 18F-FDGal was determined from linear representation of the PET data. Hepatic galactose removal kinetics were determined using measurements of hepatic blood flow and arterial and liver vein galactose concentrations at increasing galactose infusions. The hepatic removal kinetics of 18F-FDGal and galactose and the lumped constant (LC) were determined. Results The mean hepatic systemic clearance of 18F-FDGal was significantly higher in the absence than in the presence of galactose (0.274 ± 0.001 vs. 0.019 ± 0.001 L blood/min/L liver tissue; P < 0.01), showing competitive substrate inhibition of galactokinase. The LC was 0.13 ± 0.01, and the 18F-FDGal PET with galactose infusion provided an accurate measure of the local maximum removal rate of galactose (Vmax) in liver tissue compared with the Vmax estimated from arterio-liver venous (A-V) differences (1.41 ± 0.24 vs. 1.76 ± 0.08 mmol/min/L liver tissue; P = 0.60). The first-order hepatic systemic clearance of 18F-FDGal was enzyme-determined and can thus be used as an indirect estimate of galactokinase capacity without the need for galactose infusion or knowledge of the LC. Conclusion 18F-FDGal PET/CT provides an accurate in vivo measurement of human galactose metabolism, which enables the quantification of regional hepatic metabolic function.

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Background & Aims There is a clinical need for methods that can quantify regional hepatic function noninvasively in patients with cirrhosis. Here we validate the use of 2-[18F]fluoro-2-deoxy-d-galactose (FDGal) PET/CT for measuring regional metabolic function for this purpose and apply the method to test the hypothesis of increased intrahepatic metabolic heterogeneity in cirrhosis. Methods Nine cirrhotic patients underwent dynamic liver FDGal PET/CT with blood samples from a radial artery and liver vein. Hepatic blood flow was measured by indocyanine green infusion/Fick’s principle. From blood measurements, hepatic systemic clearance (Ksyst, l blood/min) and hepatic intrinsic clearance (Vmax/Km, l blood/min) of FDGal were calculated. From PET data, hepatic systemic clearance of FDGal in liver parenchyma (Kmet, ml blood/ml liver tissue/min) was calculated. Intrahepatic metabolic heterogeneity was evaluated in terms of coefficient of variation (CoV, %) using parametric images of Kmet. Results Mean approximation of Ksyst to Vmax/Km was 86% which validates the use of FDGal as PET tracer of hepatic metabolic function. Mean Kmet was 0.157 ml blood/ml liver tissue/min, which was lower than 0.274 ml blood/ml liver tissue/min previously found in healthy subjects (p <0.001) in accordance with decreased metabolic function in cirrhotic livers. Mean CoV for Kmet in liver tissue was 24.4% in patients and 14.4% in healthy subjects (p <0.0001). The degree of intrahepatic metabolic heterogeneity correlated positively with HVPG (p <0.05). Conclusions A 20 min dynamic FDGal PET/CT with arterial sampling provides an accurate measure of regional hepatic metabolic function in patients with cirrhosis. This is likely to have clinical implications for assessment of patients with liver disease as well as treatment planning and monitoring.

Good to high conversions (70–100 %) into optically active tri‐ or tetracyclic nitrogen‐containing compounds 1 based on 1,2‐dihydroisoquinolines and 1,2‐dihydrophthalazines proceed with high diastereoselectivity (d.r.≥15:1) and good to excellent enantioselectivity (85–96 % ee) in the presence of a chiral amine.