title: Operational lumped constant for FDG in normal adult male rats.
abstract: We determined an operational value for the lumped constant to be used in measurements of the local rate of cerebral glucose use (lCMR(glc)) with FDG in normal adult male rats.
  
  
  METHODS
  The standard quantitative autoradiographic method was used with 2-deoxy-d-(14)C-glucose ((14)C-DG) and with (14)C-FDG in awake normal adult male rats. Timed arterial blood samples were drawn for 45 min after the bolus and assayed for plasma glucose and (14)C concentrations. At the end of the 45-min experimental period, the rats were killed, and their brains were removed and divided in half sagittally. One hemisphere was immediately frozen and assayed for local (14)C concentrations by quantitative autoradiography; the other was weighed, homogenized in t-octylphenoxypolyethoxyethanol solution, and assayed for (14)C concentrations in the whole brain by liquid scintillation counting. Paired rats (3 pairs), one in each pair receiving (14)C-DG and the other receiving (14)C-FDG, were studied in parallel on the same day. Additional unpaired animals (n = 8) were studied with either (14)C-DG or (14)C-FDG but not in parallel on the same day. To calculate the lCMR(glc) in rats studied with (14)C-FDG, the rate constants for (14)C-FDG were estimated from the (14)C-DG values determined for rats and the (14)C-FDG/(14)C-DG ratios determined for humans. In all of the rats studied with either (14)C-DG or (14)C-FDG, the lCMR(glc) was first calculated in 12 representative brain structures with the lumped constant of 0.48 previously determined for (14)C-DG in rats. The ratio of the lCMR(glc) thus determined with (14)C-FDG to that determined with (14)C-DG for each structure was then multiplied by the lumped constant for (14)C-DG to estimate the lumped constant for (14)C-FDG. The lCMR(glc) and the lumped constant for FDG in the brain as a whole were similarly estimated from the tracer concentrations in the brain homogenates.
  
  
  RESULTS
  The mean values for the lumped constant for FDG were found to be 0.71 and 0.70 in the autoradiographic assays and the assays with brain homogenates, respectively.
  
  
  CONCLUSIONS
  The appropriate value for the lumped constant to be used in determinations of the lCMR(glc) in normal adult male rat studies with (18)F-FDG and small-animal PET scanners is 0.71.
authors.affiliation: Positron Emission Tomography Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Joji
authors.initials: J
authors.lastname: Tokugawa
authors.forename: Laura
authors.initials: L
authors.lastname: Ravasi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Nakayama
authors.forename: Kathleen C
authors.initials: KC
authors.lastname: Schmidt
authors.forename: Louis
authors.initials: L
authors.lastname: Sokoloff
mesh_terms: D000818:Animals; D001345:Autoradiography; D001794:Blood Pressure; D001921:Brain / Q000473:pathology; D003847:Deoxyglucose / Q000378:metabolism; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D008297:Male; D049268:Positron-Emission Tomography / Q000295:instrumentation* / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D003847:Deoxyglucose