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Neural Plast. 2018 Jun 12;2018:6120925. doi: 10.1155/2018/6120925. eCollection 2018.

Impact of Global Mean Normalization on Regional Glucose Metabolism in the Human Brain.

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Department of Radiology & Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.
Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.
Departments of Nuclear Medicine and Clinical Research, Odense University Hospital, University of Southern Denmark, Odense, Denmark.
Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
Chaire de Recherche Harland Sanders, School of Optometry, University of Montreal, Montreal, Canada.
Neuropsychiatry Laboratory, Psychiatric Centre, Rigshospitalet, Copenhagen, Denmark.
GIGA-Consciousness, Coma Science Group, Université de Liège, Liège, Belgium.
Departments of Neuroradiology, Nuclear Medicine and Neuroimaging Center, Technische Universität München, München, Germany.
Department of Anesthesiology, University of California, Irvine, CA, USA.


Because the human brain consumes a disproportionate fraction of the resting body's energy, positron emission tomography (PET) measurements of absolute glucose metabolism (CMRglc) can serve as disease biomarkers. Global mean normalization (GMN) of PET data reveals disease-based differences from healthy individuals as fractional changes across regions relative to a global mean. To assess the impact of GMN applied to metabolic data, we compared CMRglc with and without GMN in healthy awake volunteers with eyes closed (i.e., control) against specific physiological/clinical states, including healthy/awake with eyes open, healthy/awake but congenitally blind, healthy/sedated with anesthetics, and patients with disorders of consciousness. Without GMN, global CMRglc alterations compared to control were detected in all conditions except in congenitally blind where regional CMRglc variations were detected in the visual cortex. However, GMN introduced regional and bidirectional CMRglc changes at smaller fractions of the quantitative delocalized changes. While global information was lost with GMN, the quantitative approach (i.e., a validated method for quantitative baseline metabolic activity without GMN) not only preserved global CMRglc alterations induced by opening eyes, sedation, and varying consciousness but also detected regional CMRglc variations in the congenitally blind. These results caution the use of GMN upon PET-measured CMRglc data in health and disease.

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