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@@ Introduction The brain represents about 2％of the total body weight．but consumes about 20％of the total energy．The energy demand of the brain is met primarily by aerobic metabolism．Therefore，cerebral metabolic rate of oxygen(CMRO2)is all important index of tissue viability and brain function．Many conditions are related to alterations in oxygen metabolism,such as Huntington’S disease，Alzheimer’S disease and normal aging．In addition，quantitative measurement of CMRO2 is useful in understanding normal cerebral physiology during resting state，sleep，brain activation and physiologic challenges．The measurement of CMRO2 is not yet a routine procedure．Currently available techniques for CMRO2 measurement require the infusion／injection／inhalation of exogenous agent．