LCBF values decline while L? values increase during normal human aging measured by stable xenon-enhanced computed tomography

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Abstract
Results of measurements of LCBF and Lλ values utilizing optimal CT-CBF methods under resting conditions are reported among thirty-two neurologically normal volunteers aged between 20 and 88 years. Measurements were made during inhalation of 26–30% stable xenon gas for 8 min and serial scanning utilizing a state-of the-art CT scanner with both eyes closed and ears unplugged. LCBF values for cortical gray matter were lowest in occipital cortex and highest in frontal cortex. Gray matter flow values were also high in subcortical structures with highest values measured in the thalamus. For white matter, highest flow values were measured in the internal capsule. Changes in LCBF and Lλ values were analyzed with respect to advancing age. Significant age-related declines in LCBF values were observed in occipital cortex and frontal white matter. Significant age-related increases in Lλ values were measured in frontal and temporal cortex, caudate nucleus and thalamus. Possible explanations are offered for these age-related increases in Lλ values for gray matter, such as accumulation of lipofuscin in neurons and relative compacting of gray matter with advancing age. The latter increases the numbers of nerve cells sampled per volume of gray matter measured.