Measuring the global cerebral metabolic rate of oxygen (CMRO(2)) is a valuable tool for assessing brain vitality and function. Measurement of blood oxygen saturation (HbO(2)) and flow in the major cerebral outflow and inflow vessels can provide a global estimate of CMRO(2). We demonstrate a rapid noninvasive method for quantifying CMRO(2) by simultaneously measuring venous oxygen saturation in the superior sagittal sinus with magnetic resonance susceptometry-based oximetry, a technique that exploits the intrinsic susceptibility of deoxygenated hemoglobin, and the average blood inflow rate with phase-contrast magnetic resonance imaging. The average venous HbO(2), cerebral blood flow, and global CMRO(2) values in eight healthy, normal study subjects were 64%+/-4%, 45.2+/-3.2 mL per 100 g per minute, and 127+/-7 micromol per 100 g per minute, respectively. These values are in good agreement with those reported in literature. The technique described is noninvasive, robust, and reproducible for in vivo applications, making it ideal for use in clinical settings for assessing the pathologies associated with dysregulation of cerebral metabolism. In addition, the short acquisition time (approximately 30 seconds) makes the technique suitable for studying the temporal variations in CMRO(2) in response to physiologic challenges.

Neonatal congenital heart disease (CHD) is associated with altered cerebral hemodynamics and increased risk of brain injury. Two novel noninvasive techniques, magnetic resonance imaging (MRI) and diffuse optical and correlation spectroscopies (diffuse optical spectroscopy (DOS), diffuse correlation spectroscopy (DCS)), were employed to quantify cerebral blood flow (CBF) and oxygen metabolism (CMRO 2 ) of 32 anesthetized CHD neonates at rest and during hypercapnia. Cerebral venous oxygen saturation (S v O 2 ) and CBF were measured simultaneously with MRI in the superior sagittal sinus, yielding global oxygen extraction fraction (OEF) and global CMRO 2 in physiologic units. In addition, microvascular tissue oxygenation (StO 2 ) and indices of microvascular CBF (BFI) and CMRO 2 (CMRO 2i ) in the frontal cortex were determined by DOS/DCS. Median resting-state MRI-measured OEF, CBF, and CMRO 2 were 0.38, 9.7 mL/minute per 100 g and 0.52 mL O 2 /minute per 100 g, respectively. These CBF and CMRO 2 values are lower than literature reports for healthy term neonates (which are sparse and quantified using different methods) and resemble values reported for premature infants. Keywords: cerebral blood flow; cerebral hemodynamics; diffuse optics; MRI; near-infrared spectroscopy; neonatal ischemia INTRODUCTION Congenital heart disease (CHD) affects B35,000 neonates each year in the United States. These patients suffer both short-and long-term neurologic sequelae. Periventricular leukomalacia is the most common cerebral injury found in this population. This type of injury is characterized by focal necrosis in the periventricular white matter, and it is associated with pyknotic glial nuclei and reactive gliosis. 1,2 During the early stages of brain development, the oligodendrocyte (brain glial cells) precursors are metabolically very active and highly susceptible to injury from reduced blood flow and oxygen delivery. Hence, hypoxiaischemia has been implicated as a major cause of this injury in CHD neonates.Periventricular leukomalacia leads to impaired myelination and has been linked to worse neurodevelopmental outcomes in premature infants and postulated to cause (at least in part) the impaired cognition and cerebral palsy commonly seen in this cohort of infants with CHD. 3,4 Quantification of the hemodynamic and metabolic state of these neonates via measurements of cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen consumption (CMRO 2 ) should provide valuable information toward understanding the interaction between cardiac pathophysiology and subsequent cerebral health. Potentially, such new knowledge could help predict and prevent adverse outcomes.

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Positron emission tomography (PET) using L-[methyl-(11)C]-methionine (MET) is the most popular amino acid imaging modality in oncology, although its use is restricted to PET centers with an in-house cyclotron facility. This review focuses on the role of MET-PET in imaging of cerebral gliomas. The biological background of tumor imaging with methionine is discussed with particular emphasis on cellular amino acid transport, amino acid utilization in brain, normal metabolism of methionine, and its alterations in cancer. The role of MET-PET in clinical management of cerebral gliomas in initial diagnosis, differentiation of tumor recurrence from radiation injury, grading, prognostication, tumor-extent delineation, biopsy planning, surgical resection and radiotherapy planning, and assessment of response to therapy is also reviewed in detail.

The effect of hypercapnia on cerebral metabolic rate of oxygen consumption (CMRO 2 ) has been a subject of intensive investigation and debate. Most applications of hypercapnia are based on the assumption that a mild increase in partial pressure of carbon dioxide has negligible effect on cerebral metabolism. In this study, we sought to further investigate the vascular and metabolic effects of hypercapnia by simultaneously measuring global venous oxygen saturation (S v O 2 ) and total cerebral blood flow (tCBF), with a temporal resolution of 30 seconds using magnetic resonance susceptometry and phase-contrast techniques in 10 healthy awake adults. While significant increases in S v O 2 and tCBF were observed during hypercapnia (P < 0.005), no change in CMRO 2 was noted (P > 0.05). Additionally, fractional changes in tCBF and end-tidal carbon dioxide (R 2 = 0.72, P < 0.005), as well as baseline S v O 2 and tCBF (R 2 = 0.72, P < 0.005), were found to be correlated. The data also suggested a correlation between cerebral vascular reactivity (CVR) and baseline tCBF (R 2 = 0.44, P = 0.052). A CVR value of 6.1% ± 1.6%/mm Hg was determined using a linear-fit model. Additionally, an average undershoot of 6.7%±4% and 17.1%±7% was observed in S v O 2 and tCBF upon recovery from hypercapnia in six subjects.