Positron Emission Tomographic Measurement of Cerebral Blood Flow and Permeability—Surface Area Product of Water Using [<sup>15</sup>O]Water and [<sup>11</sup>C]Butanol

139

107

Hypercapnia induces cerebral vasodilation and increases cerebral blood volume (CBV), and hypocapnia induces cerebral vasoconstriction and decreases CBV. Cerebral blood volume measured by positron emission tomography (PET) is the sum of three components, that is, arterial, capillary, and venous blood volumes. Changes in arterial blood volume (V a ) and CBV during hypercapnia and hypocapnia were investigated in humans using PET with H 2 15 O and 11 CO. Arterial blood volume was determined from H 2 15 O PET data by means of a two-compartment model that takes V a into account. Baseline CBV and values during hypercapnia and hypocapnia in the cerebral cortex were 0.03470.003, 0.03870.003, and 0.03170.003 mL/mL (mean7s.d.), respectively. Baseline V a and values during hypercapnia and hypocapnia were 0.01570.003, 0.02570.011, and 0.0077 0.003 mL/mL, respectively. Cerebral blood volume changed significantly owing to changes in PaCO 2 , and V a changed significantly in the direction of CBV changes. However, no significant change was observed in venous plus capillary blood volume ( ¼ CBVÀV a ). This indicates that changes in CBV during hypercapnia and hypocapnia are caused by changes in arterial blood volume without changes in venous and capillary blood volume.

Section: Discussionmentioning

confidence: 99%

Changes in the Arterial Fraction of Human Cerebral Blood Volume during Hypercapnia and Hypocapnia Measured by Positron Emission Tomography

Ito

Ibaraki

Kanno

et al. 2005

139

107

“…The limited extraction of 1 5 0-water should also cause another error in calculating CBF, as demon strated by Herscovitch et al (1987). However, the calculation of the distribution volume was indepen dent of the limited extraction fraction, because E was cancelled out by dividing kl by k2' as expected from Eq.…”

Section: Cbf Measurementmentioning

confidence: 96%

A Determination of the Regional Brain/Blood Partition Coefficient of Water Using Dynamic Positron Emission Tomography

Iida

Kanno

Miura

et al. 1989

Summary:In order to investigate the validity of the single compartment model in measuring CBF with the use of 150-labeled water (H2150), dynamic positron emission to mography (PET) was performed following bolus injection of H2150. Careful attention was paid to accuracy in the measurement system (especially for the input function). In the region of the putamen, which includes the smallest mixture of gray and white matters in addition to the small est contamination of cerebrospinal fluid (CSF) spaces, the partition coefficient obtained was 0.88 ± 0.06 (ml/g).The discrepancy from the prediction estimated from the brainlblood water content ratio was only 7%. This finding suggests that there is no more complicated model than the Over the last decade, various techniques for in vivo measurement of CBF have been developed us ing 150-labeled water (H2150) and positron emission tomography (PET) (Frackowiak et aI., 1980; Lam mertsma et aI., 1981 Lam mertsma et aI., , 1982 Huang et aI., 1982 Huang et aI., , 1983 Raichle et aI., 1983; Herscovitch et aI., 1983;Kanno et al., 1984Kanno et al., , 1987 Alpert et aI., 1984; Koeppe et aI., 1985; Iida et aI., 1986). In these reports, single com partment approximation (Kety, 1951(Kety, , 1960) is com monly employed for modeling the tracer kinetics.Recently, some investigators have raised concern about the accuracy of this model. Their questions were based on the following unexpected observa- Received November 17, 1988; revised June 5, 1989; accepted June 14, 1989.Address correspondence and reprint requests to Dr. H. Iida, Department of Radiology and Nuclear Medicine, Research In stitute for Brain and Blood Vessels, Akita, 6-10 Senshuu Kubota-Machi, Akita City, Akita, 010 Japan.Abbreviations used: CBV, cerebral blood volume; C150, 150_ labeled carbon monoxide; DP, dorsalis pedis artery; FA, femoral artery; H2150, 150-labeled water; LV, left ventricle of heart; PET, positron emission tomography; PVE, partial-volume effect; RA, radial artery; ROI, region of interest. 874usual single compartment one to describe the physiolog ical behaviour of 150 water. On the other hand, in the other cortical regions, the discrepancy was larger (e.g., about 12% for the insular cortex and 26% for the frontal cortex) than in the region of the putamen, and a signifi cant fit-interval dependence was observed in the calcu lated parameters. These observations suggest a signifi cant effect of tissue heterogeneity and/or contamination with nonperfusable spaces in actual clinical PET data. Other possible explanations for the above phe nomena have also been explored from the point of view of inaccuracies in the measurement system, i.e., timing error in the input function (Iida et aI., 1988a; Koeppe et aI., 1987; Dhawan et aI., 1986)

“…It is evident that PWI differs substantially from the PET-based CBF measurement where the activity of a partly diffusible tracer (15O-H 2 O) is measured using an AIF derived from the radial artery (Herscovitch et al, 1987). The use of PWI for blood flow measurement includes several important steps:…”

Section: Imaging Of Hypoperfusionmentioning

confidence: 99%

Refining the Mismatch Concept in Acute Stroke: Lessons Learned from PET and MRI

Sobesky

2012

110

In ischemic stroke, positron-emission tomography (PET) established the imaging-based concept of penumbra. It defines hypoperfused, but functionally impaired, tissue with preserved viability that can be rescued by timely reperfusion. Diffusion-weighted and perfusion-weighted (PW) magnetic resonance imaging (MRI) translated the concept of penumbra to the concept of mismatch. However, the use of mismatch-based patient stratification for reperfusion therapy remains a matter of debate. The equivalence of mismatch and penumbra, as well as the validity of the classical mismatch concept is questioned for several reasons. First, methodological differences between PET and MRI lead to different definitions of the tissue at risk. Second, the mismatch concept is still poorly standardized among imaging facilities causing relevant variability in stroke research. Third, relevant conceptual issues (e.g., the choice of the adequate perfusion measure, the best quantitative approach to perfusion maps, and the required size of the mismatch) need further refinement. Fourth, the use of single thresholds does not account for the physiological heterogeneity of the penumbra and probabilistic approaches may be more promising. The implementation of this current knowledge into an optimized state-of-the-art mismatch model and its validation in clinical stroke studies remains a major challenge for future stroke research.