Abstract
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Objectives: The operational equation reported by Sokoloff was modified and has been used to calculate the cerebral glucose metabolic rate (cMRglc) with FDG autoradiography or PET imaging for decades. The FDG rate constants, the K*1, k*2 and k*3, of murine brain tissue, were not available, so researchers used the values from rat brains to calculate the cMRglc when mice were studied. The aim of this study was to determine the FDG rate constants of mouse brain so that cMRglc in mice can be calculated more reliably. Methods: Thirteen normoglycemic C57/BL6 male mice (19-28.5g) were studied by small animal PET imaging. Anesthetized with 1.5% isoflurane, each mouse was scanned for 60 minutes. Eighteen blood samples, 0.2 µL each, were taken from the femoral artery by a microfluidic blood sampling device. The FDG in plasma were estimated from the blood samples by using an equation reported previously. To derive tissue time activity curves (TACs), the regions of the parietal cortex were drawn on fused PET-CT images and superimposed to the 60-minute dynamic PET images. The K*1, k*2, k*3 and k*4 were estimated by a three-compartment FDG model by using the Kinetic Imaging System (KIS). For comparison, the cMRglc were also calculated by using the equation cMRglc = [Glc] *K*FDG/LC, where K*FDG=K*1*k*3/ (k*2+k*3). LC is the lumped constant and [Glc] is the glucose concentration. Results: FDG model fitted well the brain TAC (r=0.94±0.03; n=13) in all studies. The K*1, k*2, k*3, k*4 and K*FDG are 0.22±0.05 ml/min/g, 0.48±0.09 min-1, 0.059±0.018 min-1, 0.025±0.010 min-1 and 0.024±0.007 ml/min/g, respectively. The cMRglc are 24.4±7.7 umol/100g/min, using a LC value of 0.625. Conclusions: We reported the FDG rate constants for normal mouse brain for the first time. The determined cMRglc based on these values were comparable to those (26.3±6.1 umol/100g/min, n= 7) reported by Toyama et al. (2004). Using the mean values of the rate constants in the operational equation improves reliability of the calculation of cMRglc.
Research Support (if any): This work was supported by the UC Discovery Grant bio05-1050, RO1-EB001943 and DOE DE-FC03-02ER63420.
- Society of Nuclear Medicine, Inc.