Parametric PET images of CMRglu acquired at baseline (Left) and during 1-mg/kg i.v. cocaine (Right) in an anesthetized nonpregnant female baboon brain (transaxial views) from group 3. The scale bar at the bottom of the PET images provides the color-coded hue correspondence of the glucose utilization rate measured as micromole per 100 g per minute. It is clear from the quantitative PET CMRglu images that the acute i.v. challenge of cocaine reduces the CMRglu globally in the baboon brain. On average, in group 3, the CMRglu at baseline was 11.6 ± 2 μg/100 g per min and decreased significantly to 8.0 ± 1.9 μmol/100 g per min (P = 0.028) during 1 mg/kg cocaine exposure.

(A) A parametric PET image of an anesthetized pregnant M. radiata (sagittal view) of the local metabolic rate of glucose calculated based on the fetal brain time activity curve (as well as a fetal plasma glucose of 2.8 μmol/L) in a normal, pregnant M. radiata (group 1) and the corresponding T2-weighted MRI image, demonstrating the anatomical position of the fetal brain. The scale bar at the bottom of the PET images provides the color-coded hue correspondence of the glucose utilization rate measured as micromole per 100 g per min in the parametric image (except for the area corresponding to the maternal bladder, which appears as a bright red homogenous area). The color-coded scale helps illustrate that the CMRglu of the fetal brain approximated 7 to 8 μmol/100 g per min in this particular M. radiata fetus. (B) Parametric PET image of the local metabolic rate of glucose, also calculated based on the fetal brain time activity curve (fetal plasma glucose of 2.8 mmol/L) in a pregnant M. radiata exposed to 1-mg/kg cocaine i.v. (group 2); and the corresponding T2-weighted MRI image demonstrating the position of the fetal brain. Again, the scale bar at the bottom of the PET images provides the color-coded hue correspondence of the glucose utilization rate measured as micromole per 100 g per min in the parametric PET image (except for the maternal bladder) and is scaled identical to the control image in A for direct comparison. The blue colors represent the low values (0–10 μmol/100 g per min), and yellow and red colors represent higher values (approximately >10–15 μmol/100 g per min). The average CMRglu of the fetal brain in this particular M. radiata fetus approximated 10 μmol/100 g per min. Note the two symmetrical hot spots in the fetal brain, which appear in a location likely to correspond to the striatum. On average, the fetal CMRglu increased 2-fold (P < 0.01) from 5.1 ± 3.1 μg/100 g per min to 11.5 ± 2.5 μg/100 g per min during exposure to 1-mg/kg cocaine, while the maternal CMRglu increased from 10.1 ± 7.6 μg/100 g per min to 20.5 ± 3.9 μg/100 g per min (P = 0.037).

Calculation of the CMRglu in the maternal brain using commercially available software (PMOD) is illustrated. The maternal left-ventricle time-activity curve is obtained from the maternal heart and used as the arterial input function for calculation of CMRglu using the Gjedde-Patlak plot approach. The graphical analysis of the Gjedde-Patlak plot is shown; the regression line is fitted to the last three to four points of the curve and the slope of the linear phase of the plot is the uptake rate constant K_i (ml tissue/mL plasma)min⁻¹ from which the CMRglu is calculated (41).