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Purpose: This study was undertaken to explore the mechanisms underlying cognitive reserve in subjects with mild memory deficits by using positron emission tomography (PET)., Methods: Global cerebral blood flow (gCBF) and cerebrovascular reserve (CVR) measurements were performed in 15 elders (5 men, 10 women, 62-84, 71.8 +/- 6.2 years) meeting criteria for mild cognitive impairment (MCI). PET consisted of quantitative [(15)O]water determinations of CBF, two at baseline and one postadministration of acetazolamide (ACZ)., Results: Mean gCBF were 44.9 +/- 5.5 during counting, 44.5 +/- 6.7 for the memory task, and 60.2 +/- 4.8 ml/min/100 g for post-ACZ (CVR of 33.9 +/- 13.2%). Task-related gCBF change was significantly related to memory score, performance on the Trail Making Test B (Trails-B), premorbid IQ, and education, and differed significantly between the learning-based groups., Conclusions: Cognitive reserve appears analogous to cardiac reserve. The ability to alter gCBF paralleled performance on general cognitive measures, was enhanced in higher levels of cognitive reserve, and was impaired in individuals who no longer appear to benefit from repeated exposure to testing.

Purpose: Securing two intravenous lines, one for injection and one for blood sampling, can be nearly impossible in compromised patients, therefore, a need exists to quantify the potential error when simplified techniques are employed., Method: Two venous catheters were placed. 2-deoxy-2-[18F]fluoro-glucose (FDG) was infused through one of the catheters. Venous blood samples were drawn from each line. Triplicate aliquots of plasma were analyzed in duplicate., Results: Concentrations from the infusion line were 2.0% higher than the concentrations from the noninfusion line. The average error was 3.3%, 2.0%, and 0.7% higher for the first, second, and third samples, respectively., Conclusions: Blood sampling through the infusion catheter is a viable alternative to the placement of separate venous catheters. Sampling from the injection catheter, even with tubing flush and replacement, will potentially incur small (generally < 10%) over-estimations in concentration in initial samples. Subsequent sampling reduces the error to essentially zero by the third sample.

Purpose: To compile a normal database for the characterization of global [15O]water pharmacokinetic behavior., Procedures: The influences of age, gender, and body habitus on the pharmacokinetics of [15O]water were investigated in a series of normal subjects, N = 100 (50 males, 50 females, age = 19-79) who were participants in cognitive activation studies. Arterial blood was analyzed by autosampler and parametric images were constructed using a 40-second summed image and the autoradiographic model., Results: Males and females were comparable with respect to age, number of injections administered, and dose (mCi) administered per injection but differed significantly with respect to height, weight, and normalized dose (mCi/kg). There were significant gender-based differences in the bolus arrival time, global cerebral blood flow (gCBF), area-under-the-curve (AUC), summed image concentration, and dose-normalized concentration but not dose-normalized AUC. Bolus arrival time, gCBF and dose-normalized AUC were significantly influenced by age., Conclusion: Age and gender are significant determinants of [15O]water pharmacokinetic behavior.