Abstract:The O-labeled water. Over this range of Paco,, a significant linear relationship of CBV = 0.041 Paco, + 2.0 was found. For each one torr change in Paco,, there is a change in CBV of 0.041 ml/100 gm of perfused tissue. At a normocarbic value of Paco, (~37 torr), an average value of 3.5 ml/100 gm was found. A nonlinear relationship of CBV and CBF was found. This relationship is expressed in the equation, CBV = 0.80 CBF 038 . A significant linear relationship was found between CBF and Paco,. This was described by the equation, CBF = 1.8 Paco, -16.75. For each one torr change in the Paco,, there is a 1.8 ml/100 gm per minute change in the CBF. At a normocarbic value of Paco, (~37 torr), an average value of CBF of 50 ml/100 gm per minute was found. The relationship of CBV and t v was nonlinear and was expressed in the equation, t c is o = 41 CBF" 082 . Additional Key Words oxygen-15cerebral metabolic rate of oxygen

An apparatus was developed for obtaining emission transaxial images of sections of organs containing positron-emitting radiopharmaceuticals. The detection system is a hexagonal array of 24 NaI(T1) detectors connected to coincidence circuits to achieve the "electronic" collimation of annihilation photons. The image is formed by a computer-applied algorithm which provides quantitative reconstruction of the distribution of activity. Computer simulations, phantom and animal studies show that this approach is capable of providing images of better contrast and resolution than are obtained with scintillation cameras. Advantages of positron vs. single photon reconstruction tomography are discussed.

The extraction of 16 O-labeled water by the brain during a single capillary transit was studied in vivo in 20 adult rhesus monkeys by external detection of the time course of the tracer subsequent to the internal carotid injection of 0.2 ml of whole blood labeled with H, 1B O. The data showed that labeled water does not freely equilibrate with the exchangeable water in the brain when the mean cerebral blood flow exceeds 30 ml/100 g min" 1 . At the normal cerebral blood flow in the rhesus monkey (~50 ml/100 g min~'), only 90% of the H 2 15

To test the hypothesis that regional cerebral blood flow (rCBF) is normally regulated by regional metabolic activity, rCBF and the regional cerebral metabolic rate for oxygen (rCMRO2) were compared in selected human subjects. In normal subjects and patients with chronic, stable diseases of brain, rCBF correlated well with rCMRO2. In one individual with mild dementia, rCBF and rCMRO2 were measured before and during exercise of the hand and forearm contralateral to the hemisphere studied. Appropriate parallel changes occurred in both rCBF and rCMRO2 during hand exercise. In patients with acute diseases affecting the hemisphere studied, however, the correlation between rCBF and rCMRO2 was unpredictable.

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