RT Journal Article
SR Electronic
T1 Operational Lumped Constant for FDG in Normal Adult Male Rats
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 94
OP 99
VO 48
IS 1
A1 Joji Tokugawa
A1 Laura Ravasi
A1 Toshiyuki Nakayama
A1 Kathleen C. Schmidt
A1 Louis Sokoloff
YR 2007
UL http://jnm.snmjournals.org/content/48/1/94.abstract
AB We determined an operational value for the lumped constant to be used in measurements of the local rate of cerebral glucose use (lCMRglc) with FDG in normal adult male rats. Methods: The standard quantitative autoradiographic method was used with 2-deoxy-d-14C-glucose (14C-DG) and with 14C-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 14C 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 14C concentrations by quantitative autoradiography; the other was weighed, homogenized in t-octylphenoxypolyethoxyethanol solution, and assayed for 14C concentrations in the whole brain by liquid scintillation counting. Paired rats (3 pairs), one in each pair receiving 14C-DG and the other receiving 14C-FDG, were studied in parallel on the same day. Additional unpaired animals (n = 8) were studied with either 14C-DG or 14C-FDG but not in parallel on the same day. To calculate the lCMRglc in rats studied with 14C-FDG, the rate constants for 14C-FDG were estimated from the 14C-DG values determined for rats and the 14C-FDG/14C-DG ratios determined for humans. In all of the rats studied with either 14C-DG or 14C-FDG, the lCMRglc was first calculated in 12 representative brain structures with the lumped constant of 0.48 previously determined for 14C-DG in rats. The ratio of the lCMRglc thus determined with 14C-FDG to that determined with 14C-DG for each structure was then multiplied by the lumped constant for 14C-DG to estimate the lumped constant for 14C-FDG. The lCMRglc 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. Conclusion: The appropriate value for the lumped constant to be used in determinations of the lCMRglc in normal adult male rat studies with 18F-FDG and small-animal PET scanners is 0.71.