Pathophysiology of Acute Cerebral Ischemia: PET Studies in Humans

Abstract

Using positron emission tomography (PET), the combined imaging of cerebral blood flow (CBF), cerebral blood volume (CBV), tissue oxygen tension (PtO₂), oxygen extraction fraction (OEF), oxygen consumption (CMRO₂) and glucose utilization (CMRglu) has allowed to demonstrate the 3 stages of hemodynamic compromise associated with acute arterial occlusion (1) autoregulation stage (hemodynamic reserve) with elevation of CBV; (2) oligemic stage (OEF reserve) with reduced CBF, elevated OEF and normal CMRO₂, and (3) ischemic stage, with reduced CMR0₂.and elevated CMRglu/CMRO₂ ratio (anaerobic glycolysis). Sequential studies have demonstrated the transition from ischemia to tissue infarction, but also that from ischemia to eventual tissue integrity (penumbra ?); following the ischemic phase, the stage of reperfusion is well demonstrated by PET, as the luxury-perfusion syndrome. PET imaging of tissue pH has revealed that the initial stage of ischemic acidosis is followed by tissular alkalosis at reperfusion. PET has also demonstrated that functional impairment (hypometabolism) occurs at sites distant from that of ischemic injury, an effect that may partly underly the initial clinical expression of, and the ensuing functional recovery from, ischemic stroke.

Dementia due to Lacunar Infarctions: A Misnomer or a Clinical Entity?

“…(1) The strategic location of the lesion in the thala mus, corticothalamic areas or in both hemispheres [26,[49][50][51][52][53][54], (2) Positron emission tomography (PET) and single photon emission tomography studies showed that the damaged cerebral areas were more extensive than those visualized by CT scan [55][56][57], A matched decrease in cerebral blod flow (CBF) and oxygen consumption (CMRO2) may affect the whole cerebral cortex, as well as deep structures being undetected by CT scan [55,58,59]. Different altered PET patterns of CBF and CMROt in patients with ischemic infarctions are relevant to the neu rological outcome [60], and the lowest global cerebral glu cose consumption rates were found in patients with small deep infarctions [56], On the other hand, the regional CBF was significantly lower in subjects with silent lacunar lesions, this feature probably being of some relevance in detecting significant hypoperfusions far away from the lesions [61].…”

Hypoxic Viable Tissue in Human Chronic Cerebral Ischemia Because of Unilateral Major Cerebral Artery Steno-Occlusive Disease

“…5,6 Positron emission tomography (PET) using 15 O identifies areas of misery perfusion in a patient with acute ischemic stroke. 7,8 18 F-fluoromisonidazole (FMISO) is a PET marker of hypoxic but viable tissue that exists in an acute ischemic area in the human brain, [9][10][11][12] and areas with uptake of the tracer reportedly are metabolically compromised tissue at risk of infarction after acute ischemic stroke. 9,10,12 The mechanism of selective retention of 2-nitroimidazoles, including FMISO, in hypoxic tissue is not clearly understood but may involve nitroreductases.…”

PET Study of Changes in Local Brain Hemodynamics and Oxygen Metabolism after Unilateral Middle Cerebral Artery Occlusion in Baboons

“…1989; Sette et aI., 1989;Baron, 1991;Heiss et aI., 1992). These reports described the frequent occur rence of marked oxygen extraction fraction (OEF) increases in the ischemic regions within 6-48 h fol lowing onset of stroke, indicating that an oligemia!…”