TY - JOUR T1 - The Lumped Constant for the Galactose Analog 2-<sup>18</sup>F-Fluoro-2-Deoxy-<span class="sc">d</span>-Galactose Is Increased in Patients with Parenchymal Liver Disease JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 590 LP - 594 DO - 10.2967/jnumed.113.125559 VL - 55 IS - 4 AU - Kasper S. Mikkelsen AU - Michael Sørensen AU - Kim Frisch AU - Gerda E. Villadsen AU - Bo M. Bibby AU - Susanne Keiding Y1 - 2014/04/01 UR - http://jnm.snmjournals.org/content/55/4/590.abstract N2 - The galactose analog 2-18F-fluoro-2-deoxy-d-galactose (18F-FDGal) is a suitable PET tracer for measuring hepatic galactokinase capacity in vivo, which provides estimates of hepatic metabolic function. As a result of a higher affinity of galactokinase toward galactose, the lumped constant (LC) for 18F-FDGal was 0.13 in healthy subjects. The aim of the present study was to test the hypothesis of a significantly different LC for 18F-FDGal in patients with parenchymal liver disease. Methods: Nine patients with liver cirrhosis were studied in connection with a previous study with determination of hepatic intrinsic clearance of 18F-FDGal (). The present study determined the hepatic removal kinetics of galactose, including hepatic intrinsic clearance of galactose (/) from measurements of hepatic blood flow and arterial and liver vein blood galactose concentrations at increasing galactose infusions. LC for 18F-FDGal was calculated as ()/(/). On a second day, a dynamic 18F-FDGal PET study with simultaneous infusion of galactose (mean arterial galactose concentration, 6.1 mmol/L of blood) and blood samples from a radial artery was performed, with determination of hepatic systemic clearance of 18F-FDGal () from linear analysis of data (Gjedde–Patlak method). The maximum hepatic removal rate of galactose was estimated from 18F-FDGal PET data () using the estimated LC. Results: The mean hepatic of galactose was 1.18 mmol/min, the mean was 0.91 mmol/L of blood, and the mean / was 1.18 L of blood/min. When compared with values from healthy subjects, did not differ (P = 0.77), whereas both and / were significantly lower in patients (both P &lt; 0.01). Mean LC for 18F-FDGal was 0.24, which was significantly higher than the mean LC of 0.13 in healthy subjects (P &lt; 0.0001). Mean determined from the PET study was 0.019 L of blood/min/L of liver tissue, which was not significantly different from that in healthy subjects (P = 0.85). Mean hepatic was 0.57 mmol/min/L of liver tissue, which was significantly lower than the value in healthy subjects (1.41 mmol/min/L of liver tissue (P &lt; 0.0001)). Conclusion: Disease may change the LC for a PET tracer, and this study demonstrated the importance of using the correct LC. ER -