The evaluation of the lumped constant for deoxyglucose and fluorodeoxyglucose in man

The use of glucose analogues to measure local cerebral glucose metabolism (LCMRgl) is an established and powerful technique. Quantification of LCMRgl in man requires knowledge of the value of the lumped constant (LC) which describes the relationship between the uptake of the glucose analogue by the tissue to the uptake of glucose. The authors have directly measured the LC of both deoxyglucose (DG) and fluorodeoxyglucose (FDG) in 14 male volunteers using C-11 2-deoxy-D-glucose (n=6) and 18-F 2-fluoro-2-deoxy-D-glucose (n=8) respectively. In each subject the internal jugular vein and a radial artery were catheterized so that cerebral venous and arterial blood samples could be obtained. The radionuclide was infused intravenously over 50-60 minutes using an infusion schedule to produce a step change in arterial plasma radionuclide concentration and blood samples were drawn and analyzed for the determination of the extraction fraction of the tracer and of glucose. The lumped constants for deoxyglucose and fluorodeoxyglycose in man are 0.56 +- .043 (SEM) and 0.52 +- .028 (SEM) respectively. LCMRgl was determined in a series of 12 young normal volunteers using C-11 DG (n=6) and 18-F FDG (n=6) and the values of the respective LC. Average whole brain glucose consumption was determined to be 4.99 +- 0.23 mg/100 gm/min and 5.66 +- 0.37 mg/100 gm/min using C-11 DG and 18-F FDG respectively. There is no significant difference between these measurements (t=1.56, df=10) and they both agree well with reported values in the literature using the Kety-Schmidt technique