Arterial fraction of cerebral blood volume in humans measured by positron emission tomography

Abstract

In quantitative functional neuroimaging with positron emission tomography (PET) and magnetic resonance imaging (MRI), cerebral blood volume (CBV) and its three components, arterial, capillary, and venous blood volumes are important factors. The arterial fraction for systemic circulation of the whole body has been reported to be 20-30%, but there is no report of this fraction in the brain. In the present study, we estimated the arterial fraction of CBV with PET in the living human brain. C(15)O and dynamic H2(15)O PET studies were performed in each of seven healthy subjects to determine the CBV and arterial blood volume (Va), respectively. A two-compartment model (influx: K1, efflux: k2) that takes Va into account was applied to describe the regional time-activity curve of dynamic H2(15)O PET. K1, k2 and Va were calculated by a non-linear least squares fitting procedure. The Va and CBV values were 0.011 +/- 0.004 ml/ml and 0.031 +/- 0.003 ml/ml (mean +/- SD), respectively, for cerebral cortices. The arterial fraction of CBV was 37%. Considering the limited first-pass extraction fraction of H2(15)O, the true arterial fraction of CBV is estimated to be about 30%. The estimated arterial fraction of CBV was quite similar to that of the systemic circulation, whereas it was greater than that (16%) widely used for the measurement of cerebral metabolic rate of oxygen (CMRO2) using PET. The venous plus capillary fraction of CBV was 63-70% which is a important factor for the measurement of CMRO2 with MRI.

The roles of changes in deoxyhemoglobin concentration and regional cerebral blood volume in the fMRI BOLD signal

“…These values are in a good agreement with those measured using PET (Ito et al, 2001), and by other groups using NIRS (Elwell et al, 1994). This is a strong indication that these values have been determined without significant errors.…”

Correlation between arterial blood volume obtained by arterial spin labelling and cerebral blood volume in intracranial tumours

“…Instead, the volume of the blood in arteries and arterioles with a velocity over a predefined threshold (4 cm/s in our case) is measured. This threshold is to be compared to the velocities in these vessels just proximal to the capillary bed, decreasing from 10 cm/s to 0.2 cm/s, suggesting that the arteries and most of the arterioles are likely to be included in the measurement of aBV [29]. The average aBV value in healthy grey matter of 0.95 %, obtained in the present study, is well in line with previous QUASAR studies [22].…”

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

“…The V a value obtained in the present study therefore includes a part of the intravascular volume of the capillary and vein. The estimated arterial fraction of CBV (Y) is expressed with the first-pass extraction fraction of H 2 15 O and true arterial fraction (X) as (Ito et al, 2001) Y ¼ X þ ð1 À XÞð1 À EÞ E is dependent on CBF and expressed…”

“…According to this model, the radioactivity concentration in a brain region is expressed as follows (Iida et al, 1991;Ito et al, 2001;Ohta et al, 1996):…”