Regional Cerebral Blood Volume and Hematocrit Measured in Normal Human Volunteers by Single-Photon Emission Computed Tomography

Abstract

Single-photon emission computed tomography (SPECT) was used for the measurement of regional cerebral blood volume (CBV) and hematocrit (Hct) in normal healthy human volunteers (mean age 30 +/- 8 years). Regional cerebral red blood cell (RBC) volume and plasma volume were determined separately and their responses to carbon dioxide were investigated. Ten right-handed healthy volunteers were the subjects studied. SPECT scans were performed following intravenous injection of the RBC tracer (99mTc-labeled RBC) and plasma tracer (99mTc-labeled human serum albumin) with an interval of 48 h. Regional cerebral Hct was calculated as the regional ratio between RBC and plasma volumes and then was used for calculating CBV. Mean regional CBV in the resting state was 4.81 +/- 0.37 ml/100 g brain, significantly greater in the left hemisphere compared with the right by 3.8% (p less than 0.01). Mean regional RBC volumes (1.50 +/- 0.09 ml/100 g brain) were less than mean regional plasma volumes (3.34 +/- 0.28 ml/100 g brain), and mean regional cerebral Hcts were 31.3 +/- 1.8%, which was 75.9 +/- 2.1% of the large-vessel Hct. During 5% CO2 inhalation, increases in plasma volume (2.48 +/- 0.82%/mmHg PaCO2) were significantly greater than for RBC volume (1.46 +/- 0.48%/mmHg PaCO2). Consequently, the cerebral-to-large-vessel Hct ratio was reduced to 72.4 +/- 2.2%. Results emphasize the importance of cerebral Hct for the measurement of CBV and indicate that regional cerebral Hcts are not constant when shifted from one physiological state to another.

Response of Cerebral Blood Volume to Changes in Arterial Carbon Dioxide Tension in Preterm and Term Infants

“…We have assumed that the relation between optical path length Small fluctuations in [TCHb] can therefore be assumed to have and interoptode spacing was the same in infants with linear exercised a negligible effect on path length. The large vessel:cerebral hematocrit ratio has been demonstrated to change slightly with alterations in Pac02 (28). We have estimated that this introduced an error of less than 3% in the conversion of changes in [TCHb] to changes in CBV.…”

Water proton MR properties of human blood at 1.5 Tesla: Magnetic susceptibility,T1,T2,T, and non‐Lorentzian signal behavior

“…[ 16] In Eq. [16], R i,blood is the relaxation rate constant (i ϭ 1 or 2) in whole blood under susceptibility matched conditions, f plasma and f RBC are the fraction of extra-and intracellular 1 H 2 O, respectively.…”

“…We note that dependence of relaxation rate on hematocrit level may come into play in vivo, where it is known that due to the Fahraeus effect (15), Hct varies as a function of blood vessel diameter, from approximately 0.4 in large vessels to about 0.3 at the capillary level (see for example Ref. 16). …”

Absolute Arterial Cerebral Blood Volume Quantification Using Inflow Vascular-Space-Occupancy with Dynamic Subtraction Magnetic Resonance Imaging

“…Total CBV quantification in humans is possible using invasive contrast agents and MRI (Ostergaard et al, 1998;Villringer et al, 1988), positron emission tomography (Powers and Raichle, 1985), computed tomography (Steiger et al, 1993) and single photon emission computed tomography (Sakai et al, 1985).…”