SUMMARY Tomogrephic images of cerebral blood flow (CBF) and oxygen extraction fraction (OEF) using the U O continuous inhalation technique, and positron emission tomography, were obtained from a patient with cerebral ischemia distal to an occluded left internal carotid artery. There was a focal mismatch between CBF and oxygen metabolism in the brain supplied by tbe middle cerebral artery where CBF was decreased and OEF increased ("misery-perfusion syndrome" as opposed to "luxury-perfusioa syndrome"). These abnormalities were most marked in tbe parieto-ocdpital watershed area. After left superficial temporal to middle cerebral artery anastomosis, the clinical attacks ceased and a repeat study did not demonstrate tbe prerious CBF and OEF abnormalities. This suggests that this pattern of abnormalities indicates potential liable tissue. The concept of "mlsery-perfuslon" may be of some importance In tbe patbophysiological mechanisms of hemodynamic cerebral ischemia and serve as a rational basis for rerascularization procedures.

SUMMARY The oxygen-15 continuous inhalation technique and PET were used to study the age-related changes in regional CBF and CMRO 2 . Twenty-seven patients, aged 19 to 76 years, free of any history of cerebral disease and vascular risk factors were examined in "resting state." CBF, CMRO 2 and oxygen extraction fraction (OEF) values were calculated in seven different brain structures as well as in mean gray matter. Left-right ratios were also computed for all symmetrical structures analyzed.Mean gray CBF, but not mean gray CMRO 2 , decreased linearly with age (p < 0.02). However, when younger subjects (S50 yrs) were compared to older subjects (>50 yrs), an age-related matched decrease in CBF and CMRO 2 was observed in mean gray matter (18% and 17%, p < 0.05) and in all gray matter regions analyzed, particularly in frontal, temporo-sylvian and parieto-occipital cortex. White matter CBF and CMRO 2 remained remarkably stable with advancing age.Although the possibility'of methodological artifacts was considered, we favor progressive loss of cortical neurones and/or diminished activity of those remaining to explain our findings. In addition, age-related changes in cognitive activities might also be involved. Stroke Vol 15, No 4, 1984 DESPITE NUMEROUS STUDIES, 114 the effects of aging on cerebral circulation and metabolism still remain largely unsettled. Studies on global hemispheric cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO 2 ) have so far provided discrepant results: some^ concluded that CBF and CMRO 2 did not decrease with advancing age except when vascular risk factors were present, while other authors 1 2 found a parallel decline in both CBF and CMRO 2 . These discrepancies may be partially explained by different criteria for normality used. In his review on this subject, Kety 7 favored the idea that there was a rapid fall of both CBF and CMRO 2 around puberty which continued to the third decade and was followed by a more gradual decline in middle and old age.

To investigate further the topographical, clinical and temporal correlates of crossed cerebellar diaschisis (CCD) after supratentorial stroke, 55 patients suffering from a single unilateral ischaemic stroke in the carotid artery territory were studied with the quantitative oxygen-15 steady-state technique and positron tomography. Fourteen patients had one or more follow-up studies, contributing a total of 72 studies. The phenomenon of CCD, defined by depressed oxygen consumption in the contralateral cerebellum, was statistically significant in 58% of the studies. It was more prominent when the supratentorial infarct involved the internal capsule or the cortical mantle extensively, consistent with the hypothesis that it results from destruction of the corticopontocerebellar fibres. Although CCD was associated with the presence of hemiparesis, it also occurred in patients without hemiparesis and was not seen in all those with hemiparesis, suggesting that destruction of the pyramidal tract is neither necessary nor sufficient to induce CCD. Finally, CCD tended to persist over long periods of time after a stroke, pointing towards a transneuronal degeneration possibly akin to crossed cerebellar atrophy as a likely explanation for CCD. Nevertheless, CCD could be seen within hours of a stroke and sometimes disappeared within a few days, suggesting a temporal continuum between early, potentially reversible functional hypometabolism (diaschisis) and irreversible degeneration.

The functional anatomy of perceptual and semantic processings for odors was studied using positron emission tomography (PET). The first experiment was a pretest in which 71 normal subjects were asked to rate 185 odorants in terms of intensity, familiarity, hedonicity, and comestibility and to name the odorants. This pretest was necessary to select the most appropriate stimuli for the different cognitive tasks of the second experiment. The second one was a PET experiment in which 15 normal subjects were scanned using the water bolus method to measure regional cerebral blood flow (rCBF) during the performance in three conditions. In the first (perceptual) condition, subjects were asked to judge whether an odor was familiar or not. In the second (semantic) condition, subjects had to decide whether an odor corresponded to a comestible item or not. In the third (detection) condition, subjects had to judge whether the perceived stimulus was made of an odor or was just air. It was hypothetized that the three tasks were hierarchically organized from a superficial detection level to a deep semantic level. Odorants were presented with an air-flow olfactometer, which allowed the stimulations to be synchronized with breathing. Subtraction of activation images obtained between familiarity and control judgments revealed that familiarity judgments were mainly associated with the activity of the right orbito-frontal area, the subcallosal gyrus, the left inferior frontal gyrus, the left superior frontal gyrus, and the anterior cingulate (Brodmann's areas 11, 25, 47, 9, and 32, respectively). The comestibility minus familiarity comparison showed that comestibility judgments selectively activated the primary visual areas. In contrast, a decrease in rCBF was observed in these same visual areas for familiarity judgments and in the orbito-frontal area for comestibility judgments. These results suggest that orbito-frontal and visual regions interact in odor processing in a complementary way, depending on the task requirements.

Summary: With the use of positron emission tomog raphy (PET) and the 150 steady-state- [ISF]fluorode oxyglucose combined method, the local interrelationships between the cerebral metabolic rate for oxygen (CMR02) and the cerebral metabolic rate for glucose (CMRGlc) were investigated in control subjects and in stroke pa tients. In addition to the classic in vivo autoradiographic approach, a kinetic method was used to measure CMRGlc because it was expected to be more reliable in cerebral ischemia. In control subjects local coupling be tween CBF, CMR02, and CMRGlc was confirmed, and acceptable values for the CMR02/CMRGlc ratio were found; the latter, however, was lower in white matterThe recent development of independent methods for measuring in the human brain the rates of ox ygen consumption (CMR0 2 ) and glucose utilization (CMRGlc) using positron emission tomography (PET) has revived the study of the coupling be tween CMR0 2 and CMRGlc, previously restricted to the whole brain only (Finkle stein et aI., 1981; Baron et aI., 1982; Rhodes et aI., 1982). Such in vivo studies may help us understand better the con ditions required for the occurrence and the prog nostic significance of enhanced anaerobic glycol ysis in cerebral ischemia.Address correspondence and reprint requests to Dr. Baron at Service Hospitalier Frederic Joliot, CEA Departement de Biol ogie, 91406 Orsay, France.Abbreviations used: CBV, Cerebral blood volume; CMRGlc, cerebral metabolic rate for glucose; CMR02, cerebral metabolic rate for oxygen; CT, computerized tomography; GlcAV, arterio venous glucose difference; ICA, internal carotid artery; MR, metabolic ratio; OEF, oxygen extraction fraction; OM, orbito meatal; PET, positron emission tomography.140 than in gray. Uncoupling between CMR02 and CMRGlc was observed in all stroke patients, suggesting that (1) enhanced anaerobic glycolysis occurred both in reper fused recent infarcts and in chronically ischemic tissue, and (2) substrates other than blood-borne glucose were being oxidized at the borders of recent infarcts. However, methodological uncertainties presently make such obser vations only tentative. Finally, a coupled depression of CMRO, and CMRGlc was found in the contralateral cer ebellu m . Key Words: Cerebral glucose utilization-Ce rebral oxygen consumption-Oxygen-IS -Positron emission tomography. METHODS AND PATIENTS MethodsThe steady-state oxygen-IS method of measuring CBF and CMR02 (Jones et aI., 1976) was combined with the [ISF]fluorodeoxyglucose eSFDG) technique for measuring CMRGlc (Phelps et aI., 1979; Reivich et aI., 1979). A detailed account of the combined measurement has been given earlier (Baron et aI., 1982). Briefly, consecutive continuous inhalation of trace amounts of CI502 and 1502 was performed first. Once completed, 16 min (eight pe riods) were allowed to elapse before rapid (=20 s) intra venous injection of IsFDG (3-8 mCi). Generally, three contiguous head levels, parallel to the orbitomeatal (OM) line, were studied. The coincidence photons were col lected by an EC...